Supplementary Material
1. History of environmental regulations
SM Table 1 Acts and regulations in terms of regulating atmospheric emissions in Singapore (Oon & Saparudin, 2014)
Acts and regulations for general pollution2018 Environmental Protection and Management Act (Amendment of Second Schedule) Order
20182009 The Environmental Public Health (Toxic Industrial Waste) Regulations 2009.2002 Environmental Protection and Management Act (CHAPTER 94A)2000 Environmental Pollution Control (Air Impurities) Regulations 20001999 Environment Pollution Act (replace the Clean Air Act, Drainage Act, The Water Pollution and
Drainage Act)Acts and regulations for air pollution
1990 Clean Air (Standards) Regulations, Revised Edition, 19901980 The Clean Air Act (Amendment of Schedule) Notification, 19801978 The Clean Air (Standard) (Amendment) Regulations, 19781975 The Clean Air (Amendment) Act, 19751973 The Clean Air (Prohibition on the Use of Open Fires) Order, 19731972 The Clean Air (Standard) Regulations, 19721971 The Clean Air Act, 1971
2. Method of National Emission Inventory
2.1. General methods
2.1.1. Data sources
Contemporary data of the intensity of Cr-related activities, or P, from 1990 onwards, were mainly
retrieved from national statistics databases (Anti-Pollution Unit, 1971; Singapore Pollution Control
Department, 1986; Singapore Department of Statistics, 2018b) and related company websites.
Historical data of P, e.g., brick production of individual companies, were obtained from an online
archive of newspapers of Singapore (NewspaperSG, 2019) that includes The Strait Times (in its
various guises), TODAY, New Nation, Business Times.
Emission abatement efficiencies, r, were determined from a combination of the national statistical
database (Anti-Pollution Unit, 1971; Singapore Pollution Control Department, 1986; Singapore
Department of Statistics, 2018b), expert consultations (see SM section 2.1.2), and any released
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reports, including newspaper articles, dating to the period immediately following implementation of
a relevant piece of legislation. The latter was implemented to account for differences in levels of
enforcement and the effectiveness of environmental regulations relating to Cr pollution.
2.1.2. Expert consultations
Consultations were carried out with Singapore-based experts who wished to remain anonymous in
any write-up of the research, cited as a personal communication in the manuscript. For the
production subsystem, email and phone interviews were conducted with two authors of technical
reports of relevant Cr-related activities. For the consumption subsystem, three senior managers
(length of service > 25 years) from companies were interviewed in person in terms of the detailed
industrial procedures, pollution control measurements, histories and outlooks of the industry, etc.
Each interview lasted two hours on average. Two site visits were conducted in three companies
forming part of the disposal subsystem, to have a comprehensive understanding of relevant disposal
procedures. The average length of the site-visits was one hour.
2.1.3. Data validation and cross-checks
Data source triangulation (Carter et al., 2014) was conducted to validate the authenticity of the
newspaper-sourced data. For instance, estimates of the total production of conventional bricks,
electricity, total volume of incinerated waste, were compared with the estimated sum of the
production/operation capacities of individual concerns.
2.2. Subsystem 1: Manufacturing of Cr-containing products
2.2.1. Steel manufacturing
Industry introduction and Production (Psteel)
Before the 1960s, steel demands in Singapore were mainly met by import. Local manufacturing
depended on hand-operated re-rolling mills, the production of which was only 2,000 tonnes of steel
bars per year ("Task Ahead," 1964). There were no large-scale steel mills in Singapore until National
Iron and Steel Mills Limited (NISML) commenced in 1964; the output was 48,000 tonnes, using
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electric arc furnaces ("All in step with progress," 1973). Over the years, many other steel mills were
set up in Singapore. For instance, Leong Huat Industries Pte. Ltd and Webforge ("Remarkable growth
in the face of recession in world trade," 1974). The nation-owned NISML, however, was always in a
monopolistic position; its production accounted for 80% of the total steel output of Singapore in the
early 1980s ("Strong balance sheet puts NISM on firm footing," 1983). By 1989, NISML was the only
steel manufacturer remained in Singapore ("National Iron planning Malaysian joint venture," 1989).
Production of steel (Psteel) in Singapore increased from 190 thousand tonnes in 1970 to a maximum
of 764 thousand tonnes in 2008; the production dropped to 596 thousand tonnes in 2017 (see SM
Figure 1) ("National Steel Mills quadruples its spending on hi-tech," 1985; International iron and
steel institute, 2019).
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SM Figure 1 Steel production in Singapore from 1900-2017
Emission factors (EF steelair )
There are many emission factors (EFs) of Cr emissions to the atmosphere from steel manufacturing
process (EF steelair ), ranging from 0.1 g/tonne-steel to 4.5 g/tonne-steel(see SM Table 2). However,
those numbers are only valid with specific dust removal devices. Uncontrolled Cr emissions were
reported as up to 450 g/tonne-steel (Nriagu & Nieboer, 1988). In this paper, for uncontrolled
emissions from steel manufacturing, the EF steelair was set as 225 g/tonne for low emission scenario
(LES) and 450 g/tonne for high emission scenario (HES).
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SM Table 2 Emission factors for atmospheric emission from steel manufacturing
Location Year EF steelair Reference
China 2014 2.3 g/tonne-steel-steel and 4.5 g/tonne (Cheng et al., 2014)Worldwide 2001 4 g/tonne-steel (Pacyna & Pacyna, 2001)Worldwide 1988 4-40 g/tonne-steel (Nriagu & Pacyna, 1988)Worldwide 2006 0.28-16.5 wt.% of steel plant dust (Ma)The US 1988 Uncontrolled: up to 450 g/tonne steel
Controlled with Venturi scrubber: 0.1-9 g/tonne-steelControlled with bag filters: 0.1-4 g/tonne-steelControlled with electrostatic precipitator: 13.5-36.1 g/tonne-steel
(Nriagu & Nieboer, 1988)
This study-LES 225 g/tonne-steel for uncontrolled emissionsThis study-HES 450 g/tonne-steel for uncontrolled emissions
Efficiency of the dust removal device (r)
Cr emissions from steel manufacturing process were reported as exclusively in the form of particles
(Nriagu & Nieboer, 1988). Responding to the new movement of anti-pollution and abided by the
‘Clean Air Act 1971’, in 1970, NISML promised to install equipment to lessen the smoke from the mill
("Getting 'on top of old smokey'," 1970), and the company claimed that there would be “no dust and
no smoke emitted” ("Steel factory leads war on the smog," 1970). Regarding that, the efficiency of
the dust removal devices (r) in this paper was set to steadily increase from 10% in 1971 to 95% in
1980, 95% for 1980-1989, 99% for 1990-1999, and 99.5% from 2000 onwards.
Main calculation methods (E steelair )
E steelair =EF steel
air × P steel×(1−r) Equation 1
2.2.2. Conventional Brick manufacturing
Industry introduction and Production (Pbrick)
Conventional bricks refer to construction bricks that are made from clay with limited heat resistance.
The first modern brickworks, Alexandra brickworks Ltd., was established in 1899 (Labrado &
Alexandra Heritage Tour, 2017). There were many small brickworks in the 1920s; however, rather
rudimentary methods were adopted that depended on cows or buffaloes to step on earth; bricks
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were hand-shaped by workers. The turn-out was between 10,000 and 20,000 bricks each month (Sin
et al., 2015). The industry flourished over the years. Before World War II, there were at least 20 kilns
in Singapore (Zaccheus, 2014). However, during the Japanese occupation (1942 -1945), several local
small brickworks were destroyed ("Bricks Meet Demand in Singapore," 1946); the total brick
production drastically dropped to 22.2 million pieces ("Bricks Meet Demand in Singapore," 1946),
which was at the same level as the initial production of Alexandra brickworks in 1899 (Labrado &
Alexandra Heritage Tour, 2017). After the war, the brick industry revived rapidly due to the demand
from post-war constructions. However, in 1950, high retail prices of local bricks, large numbers of
imported cheaper bricks, and low demand for housing (thus low demand for bricks) heavily
impacted on the local brick industry. There were 14 brickworks in 1956, while only half remained in
1960 ("Big expansion plan for brick works," 1960). Total production of bricks gradually increased in
the following decade and reached 310 million in 1972, 70% of which were contributed by Alexandra
brickworks, the biggest brickworks in Singapore ("Builders run short of bricks, sand," 1972).
However, Alexandra brickworks ceased operation the second year because of land acquisition (Ho,
2016). The total brick production reduced to 98 million in the following year, and Jurong brickworks
became the biggest producer (Sin et al., 2015). In the meantime, the Singapore government also set
up a nation-owned brickworks ("HDB sets up $4.5 million brickworks," 1973). The brick industry
continued expanding in the following decades attributing to the island-wide public housing
construction. The brick production in 1984 reached 473 million pieces ("Building material prices
decline," 1986). In the late 1980s, however, the industry shrank due to rigid air pollution regulations
("Pollution under control here," 1989) and impacts of cheaper imported bricks from neighboring
countries where had less stringent environmental regulations ("Brick makers complain of foreign
threat," 1982). Most of the brickworks ceased operations at the end of 1990s (Sin et al., 2015) and
there was no local bulk production of bricks after 2005 (Kien, 2014) (see SM Figure 2).
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201720102003199619891982197519681961195419471940193319261919191219050
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SM Figure 2 Productions of conventional bricks in Singapore from 1900 to 2017
Emission factors (EF brickair )
Emissions of Cr mainly came from fuel burning and clay baking process. Emission factors of Cr
emissions to the atmosphere from conventional brick production (EF brickair ) was reported as
0.0255g-Cr/tonne-brick (United States Environmental Protection Agency, 1997). Many countries
have adopted this EF for inventory analyses, including Australia (Australia Department of
Environment and Energy, 1998), China (Tian et al., 2015) and the UK (Passant et al., 2002). Due
to the lack of relevant experimental data, EF brickair was set as 0.0255 g-Cr /tonne-brick - 20% for
for LES, and 0.0255 g-Cr /tonne-brick +20% for HES.
Efficiency of the atmospheric emission abatement equipment (r)
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SM Figure 3 shows, at least by the end of 1950s, the biggest and the most modernized Alexandra
brickworks was mainly dependent on high chimneys to disperse pollutants. Environmental
pollution had become a significant public concern in the 1980s as residents were suffering from
the soot and dust emitted from smoking chimneys of brickworks; the Environment Ministry
received 137 complaints about pollution from brickworks in 1983 (Anti-Pollution Unit, 1971;
Stricter measures to control pollution from brickworks, 1987). In the early 1980s, a new brick
making technique which hardens bricks by chemicals instead of burning in kilns were introduced
in Singapore. However, not many brickworks adopted the new technique ("Brickmakers prefer
to use old methods to meet shortage," 1981). The Environment Ministry also started to regulate
emissions from brickworks in the early 1980s. However, no significant alleviation was achieved
("Stricter measures to control pollution from brickworks," 1987). In 1987, another regulation
was imposed on these brickworks in Jurong district, urging them to upgrade their equipment,
change fuel types and install smoke meters ("Stricter measures to control pollution from
brickworks," 1987; "Pollution under control here," 1989). However, efficiencies of the pollution
control equipment (r) were not available. In this paper, the efficiency of the pollution control
equipment, including equipment installation rates and effectiveness of environmental policies,
was set as 0% before 1970, 10% from 1970 to 1980, and gradually increasing to 95% from 1981
to 2005.
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SM Figure 3 A painting of Alexandra Brickworks in the late 1950s, Painter: Ng Eng Teng
Main calculation methods
Ebrickair =EF brick
air × Pbrick ×(1−r ) Equation 2
2.2.3. Refractory material manufacturing
Industry introduction and Production (Prefractory)
Refractory materials refer to fire bricks or construction products that are resistant to high
temperature (> 538 °C) (United States Environmental Protection Agency, 1995). These materials are
usually used in furnaces and reaction chamber. Refractory manufacturing in Singapore has the same
length of history as that of conventional brick manufacturing, because the oldest brickworks,
Alexandra brickworks, also produced high-quality fire bricks. However, the production was not on a
large scale. Almost seven decades later, in 1966, fire bricks and other refractory construction
materials were recognized as pioneer products by the Minister of Finance despite its long
manufacturing history in Singapore ("More pioneer products for Singapore," 1966). At the end of
1960s, Singapore was predicted to become more self-sufficient in refractory materials ("Refractory
products from Jurong," 1969); Gob Bee fire-bricks Pte Ltd, one of the major refractory material
manufacturers, had a production capacity of 800 tonnes/month. By 2016, there were at least two
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companies supply refractory materials in Singapore, namely Echelon Engineering Pte Ltd (Echelon
Engineering Pte Ltd, 2018) and NSL Chemicals (NSL Chemicals, 2016). The latter has three
manufacturing factories across Southeast Asia, one of which is in Singapore (Eastech Steel Mill
Services (M) Sdn Bhd). The total output from the three factories is about 50,000 tonnes/year,
consisting of five types of refractory products, all of which contain components of either chrome ore,
magnesia-chrome or chrome-magnesia (NSL Chemicals, 2016). Due to the lack of detailed
production data (Prefractory), we did not consider the refractory production before 1966 in this
calculation. Prefractory from 1966 to 2016 were linearly interpolated based on the production data of
Gob Bee fire-bricks Pte Ltd and Eastech Steel Mill Services (M) Sdn Bhd.
Emission factors (EF refractoryair )
Emissions of Cr happen when processing Cr-containing ore to produce refractory products (United
States Environmental Protection Agency, 1995). Suppose producing one unit of refractory product
needs 1/3 unit of Cr-containing ore. Emission factors of Cr emissions to the atmosphere from
refractory production EF refractoryair was set as 0.035 kg/tonne- chromite-magnesite ore processed for
LES and 0.13 kg/tonne- chromite-magnesite ore processed for HES (United States Environmental
Protection Agency, 1995).
Efficiency of the atmospheric emission abatement equipment (r)
The efficiency of the atmospheric emission abatement equipment over the period from 1966 to
2005 was adopted from those reported in SM Section 2.2.2. For contemporary efficiency,
considering the main pollution control equipment is fiber filter, r of which was reported as 99%
(United States Environmental Protection Agency, 1995). Therefore, in this paper, r was set as 99%
for the period from 2005 to 2017.
Main calculation methods
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Erefractoryair =EFrefractory
air × Prefractory × 13
×(1−r ) Equation 3
2.2.4. Cement manufacturing
Industry introduction and Production (Pcement)
Singapore did not have cement industry until the 1960s, before which cement was all imported. In
1961, the first cement work Hong Leong Co. Ltd was established to serve the growing demand from
constructions of public housing across the country. The cement work had a production of 180,000
tonnes/year ("Singapore's first cement works to open in April," 1961). By 1972, Hong Leong Co. Ltd
was the only cement work in Singapore, and its production could not meet the domestic demand
("Singapore again faces a shortage of cement," 1972). Cement industry increased rapidly in the
1970s. By 1979, there were five factories, namely Jurong cement (500,000 tonnes/year, the biggest),
Asia Cement, Singapore Cement, Ssangyong, and Pan Malaysia cement works. The five plants had an
annum production of 2.5 million tonnes, which significantly surpassed the domestic demands (1.3
million tonnes) ("Better times ahead for cement industry," 1979). Despite the oversupply, cement
production continued to increase and reached 3.1 million tonnes/year in 1983. During the Singapore
financial recession (1985-1986), the price of cement dropped significantly, which made locally
produce cement no longer profitable. The total production of cement decreased to 1.9 million in
1985 ("Cement firms face a tough time this year," 1984). Cement industry in Singapore, however,
was still expanding. The sixth cement work commenced in 1986, which raised the total production
capacity to 5.5 million tonnes. By contrast, local demand for cement dropped to 2 million tonnes
("Cement makers claim they fall prey to dumping," 1986). Due to the high cost of labor and land and
increasingly stringent environmental regulations, the cement industry of Singapore shrank rapidly
and gradually shift away from manufacturing to trading. In 2005, the total production of cement was
150,000 tonnes (Hargreaves, 2013), which was even lower than that in 1961.
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Emission factors (EF cementair )
Emission factors of Cr emissions to the atmosphere from cement production (EF cementair ) were set as
1.0 g/tonne for LES (Cheng et al., 2014) and 2.0 g/tonne for HES (Nriagu & Pacyna, 1988).
Efficiency of the dust removal device (r)
Same as in section 2.2.2.
Main calculation methods
Ecementair =EFcement
air × Pcement ×(1−r ) Equation 4
2.2.5. Petrochemical industry - Cooling tower operations
Industry introduction and consumption (Cwatercirculating)
Cooling towers refer to evaporative cooling systems that remove heat through evaporation
(Singapore Public Utilities Board, 2017). Many industrial plants, such as power plants and
petrochemical plants, install cooling towers for cooling purposes. To prevent corrosion,
hexavalent Cr is usually added to circulated water as corrosion inhibitors (United States
Environmental Protection Agency, 1989). Singapore has a long history of utilizing cooling towers
for heat removal. In 1916, a 15-foot cooling tower was installed in a rubber factory ("Local
Industries," 1916). Singapore also hosted the largest cooling tower manufacturer (Marley
cooling tower) and the main distributor (Boustead Engineering) in Southeast Asia ("Trade Talk,"
1983). A poorly designed cooling tower emits hexavalent Cr- and bacteria-containing water
aerosol. The latter could cause infection of Legionnaires, which is a disease with a high mortality
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rate. In the 1990s, with the wide application of cooling towers, the infections of Legionnaires
increased in Singapore (Veloo, 1992; Nadarajah, 1997).
Hexavalent Cr emissions from cooling towers are associated with the total amount of water
circulating in the cooling system (Cwatercirculating). The total water consumption is proportional to the
quantity of processed oil: 1.5 barrels of freshwater is needed for processing one barrel of crude
oil; 80%-90% of the water is consumed in cooling systems (Henderson, 2016). Data on the
quantity of processed oil in Singapore were adopted from an online database (BP, 2018). SM
Figure 4 shows the water consumption from cooling systems. The water consumption rose
rapidly in the 1970s and had increased steadily in the following four decades, except a plunge in
1998 resulting from the global economic crisis. The water consumption reached 110 million
cubic meters in 2017.
Water consumption of a cooling tower consists of three parts: 1) evaporation loss 2) drift (loss of
droplets of water carried by air) 3) blowdown or bleed off (removed concentrated circulating
water) (Singapore Public Utilities Board, 2017). Evaporation loss (Pwater evap) is associated with a
temperature difference between inlet and outlet and is also dependent on meteorological
factors, such as wind and related humidity. Considering the high humidity (mean 85%) weather
of Singapore, evaporation loss from cooling towers before 1990 was estimated as 0.85% and 1%
of total circulated water for LES and HES, respectively ("Cooling towers that are light, compact,"
1976); from 1990 onward the evaporation loss was set as 0.65% and 0.85% of total circulated
water for LES and HES, respectively (CHECALC, 2016).
The volume of blowdown (Pwater blowd) is dependent on the amount of Pwater evap
and the number of
cycles of concentration (COC). The latter represents the number of times that water circulates
within a cooling system before discharge as blowdown (Singapore Public Utilities Board, 2017).
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The higher COC, the more saving on circulated water. Best Practice of Water-saving (Singapore
Public Utilities Board, 2018) recommends that COC should be at least 7 and 10 for portable
water and Newater, respectively. In this paper, from 2015 to 2017, COC was set as 7 and 10 for
LES and HES, respectively. From 2010 to 2015, COC was set as 6 and 8 for LES and HES,
respectively. From 2000 to 2010, COC was set as 5 and 7 for LES and HES, respectively. From
1980 to 2000, COC was set as 4 and 6 for LES and HES, respectively. Before 1980, COC was set as
3 and 5 for LES and HES, respectively. Pblowdown can be thus estimated by Equation 5 (CHECALC,
2016):
Pblowdown=Pwater evap
COC−1Equation 5
20172015
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SM Figure 4 Water consumption in cooling system operations in petrochemical plants from 1969 to 2017
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Production of blowdown-LES (m3) Production of blowdown-HES (m3)
SM Figure 5 Production of blowdown from cooling system operations in power plants from 1969 to 2017
Emission factors (EF coolingtowerair )
Hexavalent Cr emissions to the atmosphere from cooling towers mainly come from drift (United
States Board of Public Works, 1995). Water quality of both drift and blowdown are
approximately equal to circulating water in cooling systems (Kunz et al., 1980). In this paper, the
content of hexavalent Cr was set as 15 ppm hexavalent chromium per liter of circulating water
for LES and 20 ppm for HES (Kunz et al., 1980); Evaporated water does not contain any chemicals
(United States Board of Public Works, 1995), thus it is not considered here.
Efficiency of the drift removal device (drift generation rate) (∂)
There was no law to penalize building owners for not maintaining their cooling towers until 2002
when the Singapore government promulgated the Environmental Public Health (Cooling Towers
and Water Fountains) Regulations ("Environmental Public Health Act," 2002). All cooling towers
have since been obligated to run with pollution eliminators.
In the United States, drift loss (∂) from cooling towers that were built before 1970 was 0.1% to
0.2% of total circulated water; for cooling towers that were built after 1970, drift loss was
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reduced to 0.002% to 0.005% (Kunz et al., 1980). In the latest cooling towers technical reference
report from Public Utility Board of Singapore (Singapore Public Utilities Board, 2017), new
towers often have a drift emission of 0.02% of the recirculation rate or less. Modern drift
eliminators can achieve a drift loss of less than 0.002%. In the mid-1990s, there was a global ban
on the use of hexavalent Cr in cooling towers (United States Board of Public Works, 1995). An
interview of a government official confirmed the effective execution of the ban on the use of Cr
in cooling towers in Singapore (Anonymous, personal communication, November 8, 2018).
Considering the promulgation of the Environmental Public Health (Cooling Towers and Water
Fountains) Regulations in 2002 and the increasing premature death from Legionnaires in the
1990s, in this study, ∂ was set as 0.1% and 0.2% for LES and HES, respectively, before 2000.
From 2000 onwards, there were no Cr emissions from cooling towers in Singapore.
2016
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Production of drift-LES (m3) Production of drift-HES (m3)
SM Figure 6 Production of drift from cooling system operations in petrochemical plants
Main calculation methods
Ecoolingtowerair =EFcoolingtower
air ×Cwater circulating× ∂ Equation 6
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2.3. Subsystem 2: Consumption of Cr-containing products
2.3.1. Inland transportation – Fossil fuel combustion and tire worn
Industry introduction and consumption (C fuelcar and C tyrecar
)
Inland transportation refers to four-wheel private and public transportation. Emissions from
inland transportation consist of two parts, fossil fuel combustion and tire worn. Both types of
emissions are dependent on the number of vehicles. In 1915, the number of cars (N car) in
Singapore was 840 ("Growth of Motor Traffic," 1917). In the past century, the car numbers in
Singapore had an average increasing rate of 7% per year (see SM Figure 7), especially after
World War II ("The 60,000 mark" 1960; "Number of car trebles in 10 years" 1963). The number
of cars reached 578,233 in 2016 (Energy Market Authority, 2017).
Transportation-related fossil fuel consumption was 8000 barrels of oil (with 178,767 cars) in the
1970s("Singapore's oil pipelines," 1977), which is equal to a fuel consumption per car (α ) of 2.22
tonne of oil equivalent (toe). α reached 4.26 toe/car in 2015 (Energy Market Authority, 2017).
Total fuel combustion by car (C fuelcar) was estimated by Equation 7 (SM Figure 8). Tire worn per
kilometer traveled (∂) was set as 80 mg-tire/km (Samaras et al., 2005) and travel distance per
liter petrol (δ ) was set as 10 km/L (Land Transport Authority, 2009). Tyre-worn from cars (C tyrecar)
was estimated by Equation 8.
C fuelcar=N car × α Equation 7
C tyrecar=C fuelcar
× ∂× δ Equation 8
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SM Figure 7 Numbers of cars in Singapore from 1917 to 2017
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500,000
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Traffic related patroleum consumption (toe) Tyre worn (kg)
SM Figure 8 Transportation-related petroleum consumption and related tire-worn in Singapore from 1917 to 2017
Emission factors (EF fuelair ∧EFtyre
air )
The EFs of total Cr emissions to the atmosphere from fossil fuel consumption by transportation
were set as 5.6 ug/kg for LES and 7.4 ug/kg for HES, respectively (Pulles et al., 2012). The EFs of
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total Cr emissions to the atmosphere from tire worn were set as 0.4 mg/kg for LES and 6.73
mg/kg factor for HES, respectively (Samaras et al., 2005).
Efficiency of the dust removal device (r)
In the early 1960s, motor vehicles (168,110 cars) discharged about 103,000 tonnes of various
pollutants to the atmosphere ("'Air pollution will worsen' warning," 1971). To control traffic
pollution, from 1972 onward, all new cars were required to install crankcase emission control
devices, which could reduce emissions by 30% ("Nature's defences help Singapore," 1972). In
this paper, the vehicle scrappage rate in Singapore was set at 10% per year (Singapore Land
Transport Authority, 2019). Therefore, all cars that were registered before 1971 were scrapped
by 1981, all cars that registered after 1981 had installed with the emission control devices.
Main calculation methods
Ecarair =EF fuel
air ×C fuelcar×r+EF tyre
air ×C tyrecarEquation 9
2.3.2. Power generation- Fossil fuel combustions
Industry introduction and production (C fuelcoal , C fuel
oil ∧C fuelgas)
Emissions from power plants come from combustions of fossil fuels and solid wastes. The former
includes coal, fuel oil, and natural gas. The consumptions of fossil fuels (C fuelcoal , C fuel
oil ∧C fuelgas) were
estimated from the generated electricity (Pelectricity). In Singapore, electricity was first available at
the beginning of the 20th century; Municipal Commissioners, Singapore Tramways Company's
generation station in Mackenzie Road was the first company to supply electricity to the city from
1905 to 1924 ("The Electricity Supply" 1927). In 1924, the first official power station, St. James
power plant, started operations and generated 30,000,000 units (kwh) per year ("The Men Who
Lighten Our Darkness," 1933). With steady population growth, electricity generation increased
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by an average growth rate of 11% per year. The speed, however, slightly slowed downed over
the past four decades with an average rate of 6% per year (Singapore Department of Statistics,
2018a). In 2017, there were seven power generation plants in Singapore (except waste-to-
energy (WTE) plants) (Energy Market Authority, 2018). The total capacity of electricity
generation increased from 2 megawatts (MW) in 1926 ("The Electricity Supply," 1927) to 13,355
MW in 2017 (Energy Market Authority, 2018). Data of Pelectricity from 1971 onwards are from
Singapore Energy Statistics (Singapore Department of Statistics, 2018a). Data before 1971 were
estimated based on the correlation coefficient (β) between Pelectricity and electricity consumption
(C electricity) using Equation 10 (International Energy Agency, 2014; Singapore Department of
Statistics, 2018a), which has been reported back to 1931 ("Municipality of Singapore," 1931).
Pelectricity=Celectricity × β Equation 10
190519121919192619331940194719541961196819751982198919962003201020170
10,000,000,000
20,000,000,000
30,000,000,000
40,000,000,000
50,000,000,000
60,000,000,000
0.96
0.98
1.00
1.02
1.04
1.06
1.08
1.10
1.12
Electricity generation Ratio of generation to consumption
Elec
trici
ty g
ener
ation
Elec
trici
ty g
ener
ation
: co
nsum
ption
SM Figure 9 Total amount of electricity generated and the ratio of generated electricity and consumed electricity from
1905 to 2017
The energy structure was drastically changed over the past century (SM Figure 10). The first power
station St. James was powered by coal. With increasing the price of coal, however, all the power
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stations had switched to fuel oil to generate electricity from 1937 onwards, until the early 1990s, the
percentage of fuel oil started to reduce ("The Men Who Lighten Our Darkness," 1933). Aside from
fuel oil, in 1985, WTE plants commenced operation and generated electricity from the combustion of
solid wastes (De Koninck et al., 2017). However, WTE plants never aimed to generate electricity; the
primary purpose is to reduce waste ("Plans for 5th incineration plant for solid waste," 2013). The
electricity generated from WTE has only accounted for a small portion of the total power generation
(around 1- 3%) (De Koninck et al., 2017). In 1992, Singapore started to substitute fuel oil with natural
gas to reduce atmospheric pollution ("Natural gas now makes up 95.5% of fuel mix; renewable
energy on the rise," 2015). The ratios of electricity generated from natural gas (γgas) had since
increased rapidly. In 2004, natural gas became the primary energy source of Singapore (De Koninck
et al., 2017). In 2016, γgas rose to 95.2%, whereas the ratio of electricity generated from fuel oil (γoil)
dropped to 0.7%(Energy Market Authority, 2018). In 2014, Singapore re-started to use coal as one of
the power sources, which accounted for 1.1% of the total generated electricity (Energy Market
Authority, 2018). The electricity generated from coal (Pelectricitycoal ), fuel oil (Pelectricity
oil ) and natural gas (
Pelectricitygas ) over the past century can be estimated by Equation 11-13.
Pelectricitycoal =Pelectricity × γcoal Equation 11
Pelectricityoil =Pelectricity × γoil Equation 12
Pelectricitygas =Pelectricity × γ gas Equation 13
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201720112005199919931987198119751969196319571951194519391933192719211915190919030%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Coal % Oil % Gas % WTE%
SM Figure 10 Energy structure of Singapore from 1905 to 2017
Different types of fuel have different energy densities. One short ton of coal has an energy density of
26.57×109 J (∂coal); one barrel of crude oil has an energy density of 41.87×109 J (∂oil); 1000 ft3 of
natural gas has an energy density of 1.055×109 J (∂gas) (Bodansky, 1991). Fuel consumption is also
dependent on power plant thermal efficiency (α ). St. James power plant had a α of 16.8% for coal
combustion ("The Men Who Lighten Our Darkness," 1933). Nowadays, modern power plants can
reach an average α of 33.2% (Bodansky, 1991). Therefore, the total amount of coal (C fuelcoal), fuel oil (
C fueloil ) and natural gas (C fuel
gas) that used for electricity generation can be estimated by Equations 14-
16.
C fuelcoal=
Pelectricitycoal
α × ∂coal
Equation 14
C fueloil =
Pelectricityoil
α ×∂oil
Equation 15
C fuelgas=
Pelectricitygas
α × ∂gas
Equation 16
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401
201720102003199619891982197519681961195419471940193319261919191219050
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
Co
nsu
mp
tio
n o
f co
al (
t)
SM Figure 11 Coal consumption for power generation in Singapore from 1905 to 2016
201720102003199619891982197519681961195419471940193319261919191219050
1,000,000
2,000,000
3,000,000
4,000,000
5,000,000
6,000,000
7,000,000
8,000,000
Co
nsu
mp
tio
n o
f fu
el o
il (t
)
SM Figure 12 Petroleum consumption for power generation in Singapore from 1905 to 2016
201720102003199619891982197519681961195419471940193319261919191219050
50000000000
100000000000
150000000000
200000000000
250000000000
300000000000
Co
nsu
mp
tio
n o
f n
atu
ral g
as (
ft3
)
SM Figure 13 Natural gas consumption for power generation in Singapore from 1905 to 2016
Emission factors (EF coalair , EFoil
air∧EF gasair )
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EFs of total Cr emissions to the atmosphere from coal combustion (EF coalair ) was set as 1.7g/tonne
for LES(Pacyna & Pacyna, 2001) and 7.7 ppm for HES (Belkin et al., 2009); EFs for heavy fuel oil
were set as 1.4 mg/GJ for LES, and 5.5 mg/GJ for HES; EFs for natural gas combustion were set as
0.2 mg/GJ for LES, and 2 mg/GJ for HES(Nielsen et al., 2013).
Efficiency of the dust removal device (r)
According to interviews with local power plant managers (Anonymous, personal communication,
November 15, 2018), there is no adoption of any dust removal devices for natural gas
combustion. For fuel oil combustion, electrostatic precipitators were equipped to capture dust
with an efficiency of 80%-90% (90% is the design efficiency; nonetheless the actual operation
efficiency was usually lower than that) and flue-gas desulfurization (FGD) was installed to absorb
SO2, which is also efficient in reducing dust with around 90% of efficiency. These two dust
removal devices work in tandem; the efficiency of the whole dust removal system thus could be
98%-99%. Before 1970, there was no evidence that those old power stations installed pollution
reduction devices (Singapore Public Utilities Board, 1965, 1970). Therefore, the efficiency was
set as zero before 1970.
Main calculation methods
Epowerplant fuel
air =(EF coalair × C fuel
coal+EF oilair × C fuel
oil +EF gasair ×C fuel
gas )×(1−r) Equation 17
2.4. Subsystem 3: Disposal of Cr-containing wastes
2.4.1. Solid Waste treatment
Industry introduction and disposed of wastes (Dincinerated and Dlandfilled)
With rising GDP, per capita generation of municipal solid waste in Singapore increased from 0.22
kg/cap in 1900 (estimated from the low-income country (World Bank, 2016) to 1.37 kg/cap in
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2017 (Singapore National Environment Agency, 2019). The increase eventually leads to a rapid
rise in the total production of solid waste (Psolidwaste) (SM Figure 14). Before 1980, solid waste
grew with an average rate of 4% per year. From 1980 onwards, the rate increased to 6% per
year. Psolidwaste in 2017 was 7.7 million tonnes (Singapore National Environment Agency, 2019),
which is seven times that of the level in 1980 and 161 times that of the level in 1900.
In 1900, there was only one incineration plant, Jalan Besar incinerator, which had a capacity (CP
) of 29,700 tonnes per year ("Smells at Government House," 1900). In the following six decades,
there existed three more incinerators in Singapore, namely Alexandra incinerator (1911-1932),
Serangoon Incinerator and Kolam Ayer incinerator (1932-1959) ("Destroying Refuse," 1911; "It
All Ends In Smoke," 1936). These incinerators mainly incinerated refuse of households, garbage
of the streets, and rotten carcasses ("Destroying Refuse," 1911). Due to high operation cost
($250,000 a year for Kolam Ayer incinerator) compared with landfill, all the incinerators ceased
operations before 1959. The colonial government considered that the 40 acres of Kolam Ayer
Basin would fill up in five years and could thus be turned to a building area, which was
profitable. In the meantime, the government was promoting a low-cost type of incinerator,
placed next to trash bin centers to reduce refuse volume locally ("'Keep clean' drivein
Singapore," 1959). Another reason for abandoning incinerators is that there was no matured
atmospheric pollution control technique for clean incineration ("Machines to join battle against
trash in S'pore," 1971). Therefore, from 1960 to 1978, all collected solid wastes were locally
burned and/or landfilled. By the end of the 1970s, however, Singapore was running out of
swamp areas to dump refuse ("$50m set aside for a central refuse complex," 1972). In 1979,
after almost 20 years, a new incinerator, Ulu Pandan Incinerator (1979-2009, capacity of 584,000
t/yr), was set up on Toh Tuck Road ("Mr. Lim will open Ulu Pandan Plant today," 1979). By 2017,
there were four incinerators in Singapore, operating with a total CP of 2.8 million tonnes
(Singapore National Environment Agency, 2017a; Keppel Seghers, 2018).
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The total amount of incinerated waste (Dincinerated) is dependent on solid waste collection rate (δ
) and solid waste recycling rate (∂). In the 1930s, only the town center had the solid waste
collection; the δ was only 35%, the remainder was directly disposed to dumping grounds
("Singapore's Economic Progress Remains Steady," 1933). After years of slowly increase, δ
reached 47% in 1976 and rapidly raised to 96% by 1986. The uncollected wastes, including
unburnable wastes and chemical refuse, were still dumped at two sites: Near Tampines in the
north-east and at the end of Lim Chu Kang Road in the north-west ("So you think it's just a lot of
rubbish," 1980). Due to the large volume of solid wastes, after 1986, the government started
promoting waste recycling, especially for industrial wastes. The waste recycling rate (∂) had
increased from 0% in 1986 ("Putting more rubbish to good use," 1986; "Singapore may need to
recycle more waste," 1989) to 61% in 2017(Singapore National Environment Agency, 2017b).
The total amount of collected and unrecyclable solid wastes (DSW ) were estimated by Equation
18. Parts of DSW were burned in incinerators (Dincinerated, see Equation 19), whereas those
exceeded the total CP of incinerators were directly landfilled (Dlandfilled, not including burning
bottom ashes, see Equation 20). Dincinerated was 8,800 tonnes in 1900. The amount increased to
2.88 million tonnes in 2017. The direct landfilled wastes Dlandfilled was peaked in 1977 with
almost 1.3 million tonnes, and gradually reduced to 96,500 tonnes in 2017, attributing to the
increasing recycling rate and incineration capacities.
DSW =Psolidwaste × δ ×(1−∂) Equation 18
Dincinerated={DSW ,∧DSW <CPCP ,∧DSW ≥ CP Equation 19
Dlandfilled={ 0 ,∧DSW<CPD SW−CP ,∧D SW ≥ CP
Equation 20
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190019061912191819241930193619421948195419601966197219781984199019962002200820140
1,000,000
2,000,000
3,000,000
4,000,000
5,000,000
6,000,000
7,000,000
8,000,000
9,000,000
0%
20%
40%
60%
80%
100%
120%
Collected waste (t) Uncollected waste (t) Recycling rate % Collection rate %
SM Figure 14 Total generated solid wastes (Psolidwaste), collection rates (δ ) and recycling rates (∂) from 1900 to 2017
201720112005199919931987198119751969196319571951194519391933192719211915190919030
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
3,500,000
4,000,000
Total disposed wastes (t) Total incineration capacity (t)
SM Figure 15 Total amount of safely disposed wastes (DSW ) and capacities of incinerators (CPincinerator) from 1900 to
2017
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201720112005199919931987198119751969196319571951194519391933192719211915190919030
500,000
1,000,000
1,500,000
2,000,000
2,500,000
3,000,000
3,500,000
Incinerated solid waste(t) Direct landfilled solid waste(t)
SM Figure 16 Total amount of incinerated solid wastes (Dincinerated) and landfilled solid wastes (Dlandfilled) from 1900-
2017
Emission factors (EF flyashair )
SM Table 3 Productions and emission factors of fly ash
Location YearFly ash production
(β flyash)Cr content of
fly ash (EF flyashair ) Reference
Singapore 1991 0.01% of the total weight
(Tay & Goh, 1991)
Singapore 1993 0.023% (Goh & Tay, 1993)
Singapore 1990 0.03% by weight (Hwa, 1991)
Singapore 1997 670 mg/kg (Tan et al., 1997)
Singapore 247 ppm (37 ppm – 651 ppm)
(Bradl, 2005)
The United States 10-30 kg/tonne of feed waste
From 140 mg/kg to 530 mg/kg
(Kalogirou et al., 2010)
This study- LES 10 kg/tonne 0.01%This study- HES 30 kg/tonne 0.03%
Efficiencies of the emission reduction devices (r) and recycling rate of incineration ash (∂)
Before 1971, Singapore did not have adequate legislation and techniques for regulating atmosphere
pollution (Oon & Saparudin, 2014). Therefore, in this paper, r of emission reduction devices was set
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499
to zero before 1959. In 1979, the new incinerator installed electrostatic precipitator units to
minimize dust emissions to abide by the Clean Air Act 1971. r of the dust removal device was 99.5%
("Mr. Lim will open Ulu Pandan Plant today," 1979). Therefore, we set the efficiency as 99.5% for the
period from 1979 to 2018.
According to the Singapore National Environment Agency (2018), the recycling rate of incineration
ash (∂) had gradually increased from 7% in 2013 to 13% in 2016. Before 2013, ∂ was set to be equal
to zero.
Main calculation methods
E solidwasteair =Dincinerated× β flyash × EF flyash
air ×(1−r) Equation 21
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3. Method of Econometric Analysis
3.1. Data preparation and analysis procedure
Estimates of foreign direct investment for the period 1950-1970 were based on the quadratic
polynomial correlation between foreign direct investment and gross domestic product per capita
using data from 1970-2017 (R2=0.91). The extrapolation was conducted with three considerations: 1)
the close relationship between foreign direct investment and gross domestic product per capita can
guarantee a reasonable prediction (Chowdhury & Mavrotas, 2006). 2) This extrapolated period
covers the period before and after the independence of Singapore (1965). 3) A significant economic
improvement in the mid-1960s was witnessed in the rapid growth rate of gross domestic product
per capita and in the substantial increase in foreign-invested pioneer firms that set up in Singapore
(29 in 1963 and 111 in 1966) (Hughes & Seng, 1969).
In this study, the decision-making route for econometric analysis was chosen as follows (SM Figure
17): Step 1, test stationarities of all variables (result: all variables are stationary at first differences).
Step 2, test cointegration relationships (result: cointegration relationships exist among variables).
Step 3, run Vector Error Correction Model to test long-run and short-run relationships among
variables (result: manuscript Table 2). Step 4, run diagnostic tests for the model (result: passed all
diagnostic tests).
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SM Figure 17 Economistic analysis decision making procedure.
3.2. Unit root test
The Augmented Dickey-Fuller test checks unit root in time-series under three types of models (SM
Table 4). Null hypothesis (H0) is that the tested time series is stationary, ρ=1; H1 is that the series is
nonstationary,ρ < 1.
SM Table 4 Three types of models used in the unit root test
Type of model Equation Augmented Dickey-Fuller No intercept no trend y t=ρy t−1+μt
μt N (0 , σ2 ) ∆ y t=(ρ−1) yt−1+∑i=1
n
∂i ∆ y t−i+μt
With intercept but no trend:
y t=a+ ρyt−1+μt
μt N (0 , σ2 ) ∆ y t=a+(ρ−1) y t−1+∑i=1
n
∂i∆ y t−i+μ t
With intercept and trend y t=a+ ρyt−1+γt+μ t
μt N (0 , σ2 ) ∆ y t=a+(ρ−1) y t−1+∑i=1
n
∂i∆ y t−i+γt+μt
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533
534
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536
537
538
In this study, y = CR, GDP, GDP2, FDI, IE, and ER, respectively;ρ∧∂i= coefficients of the lagged term
of y; a=intercept ;∆ y t=yt - yt-1 ; n = lags included in the unit root test, for annual data as used in
this study, n=2 was adopted (Bhaumik, 2015).
If the probability of ρ=1 is smaller (larger) than the chosen level of statistical significance (P<0.05),
then reject (accept) H0, and accept (reject) H1 that the series is nonstationary.
One anonymous reviewer suggested that we should consider structural breaks in unit root test.
Therefore, we also conducted Zivot-Andrews unit root test (SM Table 5).
SM Table 5 Three models used in the Zivot-Andrews unit root test
Type of model Equation DenoteIntercept
∆ y t=c+αy t−1+ϵ t+γ DI t+∑i=1
n
∂i ∆ y t−i+μt
μt N (0 , σ2 )
D is a dummy variable that is used to represent the structural shift at a possible break-date. It only has two values,
DI t={0 , if t<breakdate1 , otherwise
DT t={ 0 ,if t <breakdatet−breakdate , otherwise
Trend∆ y t=c+αy t−1+ϵ t+θ DT t +∑
i=1
n
∂i ∆ y t−i+μt
μt N (0 , σ2 )With intercept
and trend ∆ y t=c+αy t−1+ϵ t+γ DI t+θ DT t+∑i=1
n
∂i ∆ y t −i+μ t
μt N (0 , σ2 )
3.3. Akaike Information Criterion, Schwarz Information Criterion and Final Prediction Error for
optimal lag selection
Akaike information criterion (AIC), Schwarz information criterion (SIC) and Final Prediction Error
(FPE) (SM Table 6) were all adopted to estimate the optimal number of lags (regressors) in this study.
The number of optimal lags is confirmed when the residual sum of squares (RSS) is the smallest. To
achieve the aim, including more regressors will significantly reduce the RSS. However, problems of
overfitting and compromising the degree of freedom might also emerge. Both AIC and SIC criterions
include a penalty term to balance the increasing number of regressors.
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SM Table 6 Equations for Akaike information criterion (AIC), Schwarz information criterion (SIC) and Final Prediction Error (FPE)
Criterion Equation after natural log transformation
AICAIC=2k
n+¿(∑ ui
2
n)
SICSIC= k
n∈n+¿(∑ ui
2
n)
FPEFPE=ui
2 (n+k )(n−k )
where, n = number of observations, in this study n= 68; k = number of lags (regressors); u=RSS ; 2kn
and kn∈n are the penalty terms of AIC and SIC, respectively. The smallest statistics of each criterion
indicates the selected optimal lag.
3.4. Johansen Cointegration Test
Cointegration exists when there are common trends among time-series variables. Cointegration rank
(r) is the number of common trends that exist among the time-series variables. With n variables, a
maximum of n-1 cointegration rank can exist to link those variables in a dynamic system. If r≠0, then
confirms the existence of cointegration relationship(s).
Two likelihood ratio (LR) tests, Maximum Eigenvalue statistic tests (Equation 22) and trace tests
(Equation 23), were adopted to test the null hypothesis to determine the cointegration rank
(Lüutkepohl et al., 2001). The first step involves a test of the null hypothesis H0, r=0, against H1, r=1.
If the p-value is larger than the chosen level of significance, then accept H0 and confirm there is no
cointegration relationship among time-series variables. Otherwise, if p-value shows the rank is
significantly different from H0, then reject H0 and accept H1 and confirm the existence of one
cointegration relationship, and continue to test a new H0 , r=1 against a new H1 , r=2. The process
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continues until the first time when H0 cannot be rejected, then the value of r can be determined
(Johansen & Juselius, 1990).
LRmaximum (r )=−T log (1−γr+1) Equation 22
LRtrace (r )=−T ∑i=r+1
n
log (1−γ i¿)¿ Equation 23
where, T is the number of observations; γi is the maximum eigenvalue.
3.5. Vector Error Correction Model (VECM)
Equation 24-28 listed short-run relationships of non-dummy variables:
∆ CRt=θ1+∑i=1
n
δ11i ∆ CRt−i+∑i=0
n
δ12 i∆ GDP t−i+∑i=0
n
δ 13i ∆ GDP2t−i+∑i=0
n
δ14 i ∆ FDI t−i+∑i=0
n
δ 15i ∆ IE t−i+δ 16i ERt+δ17D t+φ0ect t−1+μ1 t
Equation 24
∆ GDP t=θ2+∑i=1
n
δ21 i ∆ CRt−i+∑i=0
n
δ 22i ∆ GDPt−i+∑i=0
n
δ23 i ∆ GDP2t−i+∑i=0
n
δ 24 i ∆ FDI t−i+∑i=0
n
δ 25i ∆ IEt−i+δ26 i ERt+δ 27Dt +φ1 ect t−1+μ2 t
Equation 25
∆ GDP2t=θ3+∑i=1
n
δ31 i∆ CRt−i+∑i=0
n
δ32 i ∆ GDPt−i+∑i=0
n
δ33 i ∆GDP2t−i+∑i =0
n
δ34 i ∆ FDI t−i+∑i=0
n
δ35 i ∆ IE t−i+δ36 i ERt+δ37 Dt+φ2ectt−1+μ3t
Equation 26
∆ FDI t=θ4+∑i=1
n
δ 41i ∆ CRt−i+∑i=0
n
δ42 i ∆ GDPt−i+∑i=0
n
δ43 i ∆ GDP2t−i+∑i=0
n
δ 44 i ∆ FDI t−i+∑i=0
n
δ 45 i∆ IE t−i+δ 46 i ERt +δ 47Dt+φ3 ect t−1+μ4 t
Equation 27
∆ IEt=θ5+∑i=1
n
δ 51i ∆ CRt−i+∑i=0
n
δ52 i∆ GDP t−i+∑i=0
n
δ 53i ∆ GDP2t−i+∑i=0
n
δ54 i ∆ FDI t−i+∑i=0
n
δ 55i ∆ IE t−i+δ 56i ERt+δ57D t+φ4 ect t−1+μ5 t
Equation 28
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589
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593
where, ∆= deviation or first difference operator; n= optimal lag number; φ0~φ4 = error-correction
coefficients; θ1 θ5 = constant terms; δ 11i δ57 i = short-run coefficients; μ1 t μ5 t= error terms.
3.6. Granger causality test
Granger causality test measures the direction of short-run relationships through comparing the RSS
of a regression of a variable (y) with its own past (yt-1, yt-2,… yt-i) (denoted RSSR) with the RSS of a
regression of a variable with its own past and another variable’s past (xt-1, xt-2,…) (denoted RSSU). If
including the lagged terms of other variables significantly improves the regression outcome, then it
confirms that x granger causes y. The test consists of three steps (Asteriou & Hall, 2015):
First, calculate the RSS for individual time-series variables in a model only contains the lagged terms
of each variable itself.
y t=a+∑i=1
n
γi y t−i+μt Equation 29
where, y= CR, GDP, GDP2, FDI, IE, and ER; a= constant term; n= number of lags, in this case, n=3; μt=
white noise. The obtained RSSs ware denoted as RSSR-CR, RSSR-GDP, RSSR-GDP2, RSSR-FDI, RSSR-IE, RSSR-ER, and
RSSR-D.
Second, calculate the RSS for each time-series variable in a model contains the lagged terms of each
variable and lagged terms of another variable.
y t=a+∑i=1
n
γi y t−i+¿∑i=1
n
∂i x t−i+μt ¿ Equation 30
where, if y = CR, then x=GDP, GDP2, FDI, IE, ER, and D, respectively; if y= GDP, then x= CR, GDP,
GDP2, FDI, IE, ER, and D respectively, etc. Each pair of variables is examined; the obtained RSSs are
denoted as RSSU-CR-GDP, RSSU-CR-GDP… , and RSSU-ER-D.
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Third, the null hypothesis H0 : x does not granger-cause y; H1 : x granger causes y. Therefore,
calculate the F-statistics of each pair of RSSR and RSSU , e.g. RSSR−CR with RSSU−CR−GDP.
F=( RSSR−RSSU )/m
RSSU /(n−k )Equation 31
where, m= number of lagged terms of x, in Eviews, m = n, and k = n+m. If the F test statistic is larger
(smaller) than the critical value, then reject (accept) the H0, and accept (reject) H1 that x (does not)
granger causes y.
3.7. Breusch-Godfrey Serial Correlation Lagrange Multiplier (LM) Test
The Breusch-Godfrey Serial Correlation LM Test includes three steps:
First, estimate the residuals of ect t, denoted μt, and the goodness-of-fit R2 the long-run relationship
based on Ordinary Least Squares estimation procedure.
Second, regress μt with its lagged terms.
μt=∑i=1
p
γi μ t−i+ϵ t Equation 32
where γi= regression coefficients; ϵ t= white noise term. Null hypothesis, H0: there is no serial
correlation,γ1=γ2=…=γ p=0, thusμthas no relationship with its lagged terms; H1: not all
regression coefficients are equal to zero.
Third, test the null hypothesis using the chi-square method.
chisquare=(n−p )× R2 Equation 33
where, n= number of observations. When the value of chi-square is larger (smaller) than the critical
chi-square value at the chosen level of significance, reject (accept) H0, and accept (reject) H1 that
there exists serial correlation.
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3.8. Breusch-Pagan-Godfrey test for heteroskedasticity
Similar to the Breusch-Godfrey Serial Correlation LM Test, the heteroskedasticity test consists of
three steps:
First, estimate the residuals of ect t, denoted μt, based on the Ordinary Least Squares method.
Second, use Breusch-Pagan-Godfrey to formulate an artificial regression for μt squared (Equation
37). Calculate the goodness-of-fit R2 of artificial regression. H0: heteroskedasticity is not present, and
H1: heteroskedasticity is present.
μt2=β1GDPt+β2GDP2t+ β3 FDI t+β4 IEt +β5ERt+ β6 Dt+α0+ectt Equation 36
Third, test the null hypothesis using the chi-square method:
chisquare=N × R2 Equation 37
where, N = number of observations. The calculated chi-square has a chi-square distribution with S-1
degrees of freedom. If the estimated value of chi-square is larger (smaller) than the critical value of
chi-square with S-1 degrees of freedom, reject (accept) H0, and accept (reject) H1 that
heteroskedasticity is present.
4. Results
4.1. Results of national emission inventory analysis
4.1.1. Steel manufacturing
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201720112005199919931987198119751969196319571951194519391933192719211915190919030
10000
20000
30000
40000
50000
60000
70000
80000
90000
Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)
SM Figure 18 Total Cr emissions to the atmosphere from steel manufacturing
4.1.2. Conventional Brick manufacturing
201720112005199919931987198119751969196319571951194519391933192719211915190919030
10
20
30
40
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60
Total Cr emissions to air-LES (kg ) Total Cr emission to air-HES (kg)
SM Figure 19 Total Cr emissions to the atmosphere from conventional brick manufacturing
4.1.3. Refractory material manufacturing
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201720112005199919931987198119751969196319571951194519391933192719211915190919030
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Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)
SM Figure 20 Total Cr emissions to the atmosphere from refractory material manufacturing
4.1.4. Cement manufacturing
201720112005199919931987198119751969196319571951194519391933192719211915190919030
1,000
2,000
3,000
4,000
5,000
6,000
Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)
SM Figure 21 Total Cr emissions to the atmosphere from cement production
4.1.5. Petrochemical industry - Cooling tower operations
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201720
1520
1320
1120
092007
20052003
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1993
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891987
19851983
198119
791977
1975
19731971
19690
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40
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120
Cr VI drift from cooling tower (kg) - LES Cr VI drift from cooling tower (kg) - HES
SM Figure 22 Hexavalent Cr emissions to the atmosphere (through drift) from cooling system operations in petrochemical
plants
4.1.6. Inland transportation – Fossil fuel combustion and tire worn
201320082003199819931988198319781973196819631958195319481943193819331928192319180
2
4
6
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10
12
14
Total Cr emissions to air by fuel-LES (kg) Total Cr emissions to air by fuel-HES (kg)
SM Figure 23 Total Cr emissions to the atmosphere from inland transportation in Singapore
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201320082003199819931988198319781973196819631958195319481943193819331928192319180
2
4
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18
Total Cr emissions to air by tyre-LES (kg) Total Cr emissions to air by tyre-HES (kg)
SM Figure 24 Total Cr emissions to the atmosphere from car tyre-worn in Singapore
4.1.7. Power generation- Fossil fuel combustions
201720122007200219971992198719821977197219671962195719521947194219371932192719221917191219070
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Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)
SM Figure 25 Total Cr emissions to the atmosphere from fossil fuel combustion for power generation
4.1.8. Solid Waste treatment
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201720112005199919931987198119751969196319571951194519391933192719211915190919030
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Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)
SM Figure 26 Total Cr emissions to the atmosphere from centralized combustion of solid wastes
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4.2. Results of Econometric analysis
4.2.1. Unit root test
SM Table 7 Results of the Augmented Dickey-Fuller Test for Unit Root for each time-series variable except dummy variables
Variable Abbreviation
None Intercept Trend and InterceptLevel First
differenceSecond
differenceLevel First
differenceSecond
differenceLevel First
differenceSecond
difference
CR 0.2713
0.0000** 0.0000** 0.0797
0.0000** 0.0000** 0.1029 0.0000** 0.0000**
GDP 1.0000
0.0000** 0.0000** 0.9999
0.0000** 0.0000** 0.9060 0.0000** 0.0000**
GDP2 0.9994
0.0075** 0.0322** 0.9999
0.0000** 0.0000** 0.9928 0.0054** 0.0000**
FDI 1.0000
0.0000** 0.0000** 0.9996
0.0000** 0.0000** 0.9866 0.0000** 0.0000**
IE 0.9948
0.0000** 0.0000** 0.9673
0.0000** 0.0000** 0.3737 0.0000** 0.0000**
Augmented Dickey-Fuller Test, MacKinnon (1996) one-sided p-values. CR: Cr atmospheric emissions per capita; GDP: gross domestic product per capita; GDP2: GDP per capita squared; FDI: Foreign Direct Investment inflow; IE: Trade openness.Level: raw data, first difference: xt-xt-1, second difference: xt-xt-2. * reject the null hypothesis at 0.1 level, ** reject the null hypothesis at 0.05 level.Results show that all variables are stationary at the first difference.
SM Table 8 Results of Zivot-Andrews unit root test. The test includes three models, namely intercept, trend, and intercept and trend. The table reports all the probability values of the three models for data at level and at first differences, and the corresponding breakpoints.
Zivot-Andrews test statistics Models Level Prob. First different
prob. Chosen Breakpoint
CR
Intercept
0.0214** 1964
GDP 0.0083** 2004
GDP2 0.0022** 2006
FDI 0.0002** 2006
IE 0.0125** 2000
CR
Trend
0.1142 0.0013** 1979
GDP 0.0187** 1986
GDP2 0.0002** 2002
FDI 0.0000** 1999
IE 0.0321** 1983
CR
Intercept and trend
0.0003** 1976
GDP 0.0083** 2004
GDP2 0.0749* 1998
FDI 0.0041** 2006
IE 0.1143 0.0120** 2007
Null hypothesis: CR has a unit root with a structural break * reject the null hypothesis at 0.1 level, ** reject the null hypothesis at 0.05 level.
684
685
686
687688689690691692
693
694695696
697698699
SM Table 9 Results of multiple breakpoint test on the dependent variable CR.
Multiple Breakpoint test statistics on CR
(H0 vs H1*)F-statistic (critical value) Chosen Breakpoint
0 vs 1** 26.1520 (8.58) 1981
1 vs 2** 199.0255(10.13) 1964
2 vs 3 6.0381(11.14)* H0 number of breakpoints, H1 number of breakpoints +1;** Significant at the 0.05 level. Critical values are from Bai-Perron (2003).
4.2.2. Optimal lag selection
SM Table 10 Results of Akaike Information Criterion, Schwarz Information Criterion and Final Prediction Error for optimal lag selection
NO. of Lags Final Prediction Error(FPE)
Akaike information
criterion (AIC)
Schwarz information
criterion (SIC)1 8.78E+26 81.89848 83.56537*2 7.54E+26 81.69996 85.033733 9.92E+26 81.84115 86.841794 4.45E+26 80.75806 87.425595 5.74e+25* 78.18618* 86.52059
The lag number is indicated by the smallest statistic of each criterion, denoted by *.
4.2.3. Johansen Cointegration Test
SM Table 11 Results of Johansen Cointegration Test for cointegration relationship among variables
Hypothesized No. of Cointegrating
eqn(s) (r)Trace Statistic Prob.(trace)** Max-Eigen Statistic Prob.( Max-Eigen)**
H0: r=0 * 241.80 0.0000 86.53 0.0000
H0: r≤1 * 155.27 0.0000 65.90 0.0000
H0: r≤2 * 89.36 0.0007 38.28 0.0140
H0: r≤3* 51.08 0.0241 28.80 0.0348
H0: r≤4 22.28 0.2832 13.60 0.3985
* denotes rejection of the H0 hypothesis at the 0.05 level. **MacKinnon-Haug-Michelis (1999) p-values.Trace and Max-Eigen tests both indicates four cointegrating equation at the 0.05 level.
700701
702703704705706
707708
709710
711
712
713714715
716
717
718
719
720
4.2.4. Diagnostic tests
SM Table 12 Results of diagnostic tests for serial correlation and heteroskedasticity
Diagnostic test Null Hypothesis (H0) p-statistics Decision
Breusch-Godfrey Serial Correlation LM Test Exist no serial correlation 0.2024 Do not reject the H0 at the 0.05 level.
No serial correlationHeteroskedasticity Test: Breusch-Pagan-
GodfreyExist no heteroskedasticity 1.000 Do not reject the H0 at the 0.05
level.
No heteroskedasticity
721
722
723
724
725
References
$50m set aside for a central refuse complex. (1972, May 28). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19720328-1.2.52.1?ST=1&AT=filter&K=Singapore+incinerator&KA=Singapore+incinerator&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,incinerator&oref=article
The 60,000 mark. (1960, July 7). The Singapore Free Press. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/freepress19600707-1.2.64?ST=1&AT=search&k=Singapore%20number%20of%20cars&QT=singapore,number,of,cars&oref=article
'Air pollution will worsen' warning. (1971, May 21). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19710521-1.2.122?ST=1&AT=filter&K=air+pollution+control+singapore&KA=air+pollution+control+singapore&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&P=2&Display=0&filterS=0&QT=air,pollution,control,singapore&oref=article
All in step with progress. (1973, February 27). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19730227-1.2.62.1?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,steel,production&oref=article
Anti-Pollution Unit. (1971). Anti Pollution Unit Annual Report -1971-1985. Asteriou, D., & Hall, S. G. (2015). Applied econometrics: Macmillan International Higher Education.Australia Department of Environment and Energy. (1998). Emissions Estimation Technique Manual
for Bricks, Ceramics, & Clay Product Manufacturing. Retrieved from http://www.npi.gov.au/resource/emission-estimation-technique-manual-bricks-ceramics-and-clay-product-manufacturing
Bai, J., & Perron, P. (2003). Critical values for multiple structural change tests. The Econometrics Journal, 6(1), 72-78. doi:10.1111/1368-423x.00102
Belkin, H. E., Tewalt, S. J., Hower, J. C., Stucker, J., & O'Keefe, J. (2009). Geochemistry and petrology of selected coal samples from Sumatra, Kalimantan, Sulawesi, and Papua, Indonesia. International Journal of Coal Geology, 77(3-4), 260-268.
Better times ahead for cement industry. (1979, August 14). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19790814-1.2.77.2?ST=1&AT=filter&K=Singapore+cement+production&KA=Singapore+cement+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,cement,production&oref=article
Bhaumik, S. K. (2015). Principles of Econometrics: A Modern Approach Using EViews: Oxford University Press.
Big expansion plan for brick works. (1960, August 26). The Straits Times, p. 10. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19600826-1.2.106?ST=1&AT=filter&K=Jurong+brick+works&KA=Jurong+brick+works&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=jurong,brick,works&oref=article
Bodansky, D. (1991). The Energy Source Book. New York: American Institute of Physics.BP. (2018). BP Statistical Review of World Energy- Singapore Oil Refinery Capacities.
https://ycharts.com/indicators/singapore_oil_refinery_capacitiesBradl, H. (2005). Heavy Metals in the Environment: Origin, Interaction and Remediation: Elsevier
Science.Brick makers complain of foreign threat. (1982, October 26). Business Times. Retrieved from
http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19821026-1.2.10?
726
727728729730731732733734735736737738739740741742743744745746747748749750751752753754755756757758759760761762763764765766767768769770771772773774775
ST=1&AT=filter&K=Jurong+brick+works&KA=Jurong+brick+works&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=jurong,brick,works&oref=article
Brick Shortage Holds Up Spore Housing. (1947, January 9). Malaya Tribune. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/maltribune19470109-1.2.23?ST=1&AT=filter&K=singapore+clay+production+bricks&KA=singapore+clay+production+bricks&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,clay,production,bricks&oref=article
Brickmakers prefer to use old methods to meet shortage. (1981, July 6). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19810706-1.2.107.1.3?ST=1&AT=filter&K=singapore+clay+production+bricks&KA=singapore+clay+production+bricks&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,clay,production,bricks&oref=article
Bricks Meet Demand in Singapore. (1946, November 11). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19461111-1.2.24?ST=1&AT=filter&K=Alexandra+Brickworks+output&KA=Alexandra+Brickworks+output&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=alexandra,brickworks,output&oref=article
Builders run short of bricks, sand. (1972, February 29). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19720229-1.2.32?ST=1&AT=filter&K=Alexandra+Brickworks+output&KA=Alexandra+Brickworks+output&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=alexandra,brickworks,output&oref=article
Building material prices decline. (1986, March 21). Business Times Singapore. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19860321-1.2.12.9?ST=1&AT=filter&K=Brick+production+in+Singapore&KA=Brick+production+in+Singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=biztimes&CT=&WC=&YR=1986&QT=brick,production,in,singapore&oref=article
Carter, N., Bryant-Lukosius, D., DiCenso, A., Blythe, J., & Neville, A. J. (2014). The use of triangulation in qualitative research. Oncology nursing forum, 41(5), 545-547. doi:10.1188/14.ONF.545-547
Cement firms face a tough time this year. (1984, May 28). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19840528-1.2.35.7?ST=1&AT=filter&K=Singapore+cement+production&KA=Singapore+cement+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,cement,production&oref=article
Cement makers claim they fall prey to dumping. (1986, June 5). Business Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19860605-1.2.25.2?ST=1&AT=filter&K=Singapore+cement+production+5.5+m&KA=Singapore+cement+production+5.5+m&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=&WC=&YR=1986&QT=singapore,cement,production,55,m&oref=article
CHECALC. (2016). Cooling Tower Makeup Water. Retrieved from https://checalc.com/solved/ctmakeup.html
Cheng, H., Zhou, T., Li, Q., Lu, L., & Lin, C. (2014). Anthropogenic chromium emissions in China from 1990 to 2009. PloS one, 9(2), e87753.
Chowdhury, A., & Mavrotas, G. (2006). FDI and growth: what causes what? World economy, 29(1), 9-19.
Colony's Motor Traffic. (1924, September 17). The Singapore Free Press and Mercantile Advertiser. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/singfreepressb19240917-1.2.22?
776777778779780781782783784785786787788789790791792793794795796797798799800801802803804805806807808809810811812813814815816817818819820821822823824825
ST=1&AT=search&k=Singapore+number+of+cars&P=7&Display=0&filterS=0&QT=singapore,number,of,cars&oref=article
Cooling towers that are light, compact. (1976, April 18). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19760418-1.2.84.9?ST=1&AT=filter&K=cooling+tower+water+consumption+singapore&KA=cooling+tower+water+consumption+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=cooling,tower,water,consumption,singapore&oref=article
De Koninck, R., Hai, P. T., & Girard, M. (2017). Singapore's Permanent Territorial Revolution: Fifty Years in Fifty Maps: National University of Singapore Press.
Destroying Refuse. (1911, March 1). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19110301-1.2.62?ST=1&AT=search&k=cement%20dust%20eliminate%20Singapore&QT=cement,dust,eliminate,singapore&oref=articlehttp://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19340720-1.2.95?ST=1&AT=filter&K=Alexandra+Road+incinerator&KA=Alexandra+Road+incinerator&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=alexandra,road,incinerator&oref=article
Echelon Engineering Pte Ltd. (2018). Company Profile. Retrieved from https://echelon.sg/The Electricity Supply. (1927, October 20). The Straits Times. Retrieved from
http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19271020.2.54Energy Market Authority. (2017). Singapore Energy Statistics. Retrieved from
https://www.ema.gov.sg/cmsmedia/publications_and_statistics/publications/ses17/publication_singapore_energy_statistics_2017.pdf
Energy Market Authority. (2018). Singapore Energy Statistics. Retrieved from https://www.ema.gov.sg/cmsmedia/Publications_and_Statistics/Publications/SES17/Publication_Singapore_Energy_Statistics_2017.pdf
Environmental Public Health Act, G.N. No. S 37/2001, Environmental Public Health (Cooling Towers and Water Fountains) Regulations § 133, Chapter 95 Stat. (2002 31st Jan 2002).
Getting 'on top of old smokey'. (1970, April 23). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19700423-1.2.90?ST=1&AT=filter&K=air+pollution+control+singapore&KA=air+pollution+control+singapore&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&P=2&Display=0&filterS=0&QT=air,pollution,control,singapore&oref=article
Goh, A. T., & Tay, J.-H. (1993). Municipal solid-waste incinerator fly ash for geotechnical applications. Journal of Geotechnical Engineering, 119(5), 811-825.
Growth of Motor Traffic. (1917, August 25). The Singapore Free Press and Mercantile Advertiser. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/singfreepressb19170825-1.2.56?ST=1&AT=search&k=Singapore+number+of+cars&P=6&Display=0&filterS=0&QT=singapore,number,of,cars&oref=article
Hargreaves, D. (2013). The Global Cement Report: Tradeship Publications.HDB sets up $4.5 million brickworks. (1973, January 11). New Nation. Retrieved from
http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19730111-1.2.56?ST=1&AT=filter&K=singapore+clay+production+bricks&KA=singapore+clay+production+bricks&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,clay,production,bricks&oref=article
Henderson, R. (2016). Water Consumption in US Petroleum Refineries. Retrieved from the United States: https://greet.es.anl.gov/files/refineries-water-2016
826827828829830831832833834835836837838839840841842843844845846847848849850851852853854855856857858859860861862863864865866867868869870871872873874875
Ho, S. (2016). Alexandra. Retrieved from http://eresources.nlb.gov.sg/infopedia/articles/SIP_2016-06-21_114707.html
Hughes, H., & Seng, Y. P. (1969). Foreign Investment and Industrialisation in Singapore. Canberra, Australia: Australian National University Press.
Hwa, T. J. (1991). Leachate of fly ash derived from refuse incineration. Environmental Monitoring and Assessment, 19(1), 157-164. doi:10.1007/BF00401308
International Energy Agency. (2014). Electric power consumption (kWh per capita). https://data.worldbank.org/indicator/EG.USE.ELEC.KH.PC
International iron and steel institute. (2019). Steel Statistical Yearbook 1978-1978. https://www.worldsteel.org/steel-by-topic/statistics/steel-statistical-yearbook-.html
It All Ends In Smoke. (1936, February 26). Morning Tribune. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/morningtribune19360226-1.2.73?ST=1&AT=filter&K=Singapore+incinerator&KA=Singapore+incinerator&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,incinerator&oref=article
Johansen, S., & Juselius, K. (1990). Maximum likelihood estimation and inference on cointegration—with applications to the demand for money. Oxford Bulletin of Economics and Statistics, 52(2), 169-210.
Kalogirou, E., Themelis, N., Samaras, P., Karagiannidis, A., & Kontogianni, S. (2010). Fly ash characteristics from waste-to-energy facilities and processes for ash stabilization. Paper presented at the ISWA World Congress.
'Keep clean' drivein Singapore. (1959, September 16). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19590916-1.2.115?ST=1&AT=search&k=Kolam%20Ayer%20incinerator%20closed&QT=kolam,ayer,incinerator,closed&oref=article
Keppel Seghers. (2018). Waste-to-Energy Plants. Retrieved from http://www.keppelseghers.com/en/content.aspx?sid=3028
Kien, L. C. (Producer). (2014). Building Singapore Brick by Brick. Retrieved from http://justinzhuang.com/posts/tonneag/lai-chee-kien/
Kunz, R., Hess, T., Yen, A., & Arseneaux, A. (1980). Kinetic model for chromate reduction in cooling tower blowdown. Water Pollution Control Federation, 2327-2339.
Labrado & Alexandra Heritage Tour. (2017). Former Alexandra Brickworks. Retrieved from http://www.mycommunity.org.sg/tonneour-2/150-8-former-alexandra-brickworks.html
Land Transport Authority. (2009). Land transport statistics in brief 2009. Retrieved from Singapore: https://www.lta.gov.sg/content/dam/ltaweb/corp/PublicationsResearch/files/FactsandFigures
Local Industries. (1916, April 26). Malaya Tribune. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/maltribune19160426-1.2.49?ST=1&AT=filter&K=Singapore+cooling+tower&KA=Singapore+cooling+tower&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,cooling,tower&oref=article
Lüutkepohl, H., Saikkonen, P., & Trenkler, C. (2001). Maximum eigenvalue versus trace tests for the cointegrating rank of a VAR process. The Econometrics Journal, 4(2), 287-310.
Ma, G. (2006). Cr (VI)-containing electric furnace dust and filter cake: characteristics, formation, leachability and stabilization. University of Pretoria.
Machines to join battle against trash in S'pore. (1971, August 7). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19710807-1.2.56?ST=1&AT=filter&K=Chua+Chu+Kang+dumping&KA=Chua+Chu+Kang+dumping&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=chua,chu,kang,dumping&oref=article
876877878879880881882883884885886887888889890891892893894895896897898899900901902903904905906907908909910911912913914915916917918919920921922923924925926
The Men Who Lighten Our Darkness. (1933, September 10). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19330910-1.2.49?ST=1&AT=filter&K=Singapore+coal+consumption&KA=Singapore+coal+consumption&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,coal,consumption&oref=article
More pioneer products for Singapore. (1966, June 20). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19660620-1.2.95?ST=1&AT=filter&K=refractory+bricks+singapore&KA=refractory+bricks+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=refractory,bricks,singapore&oref=article
Mr. Lim will open Ulu Pandan Plant today. (1979, July 30). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19790730-1.2.134.3?ST=1&AT=filter&K=Singapore+incinerator&KA=Singapore+incinerator&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7cILLUSTRATION&WC=&YR=&P=2&Display=0&filterS=0&QT=singapore,incinerator&oref=article
Municipality of Singapore. (1931, August 24). Malaya Tribune. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/maltribune19310824-1.2.3?ST=1&AT=filter&K=MacRitchie+Reservoir+water+level&KA=MacRitchie+Reservoir+water+level&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=macritchie,reservoir,water,level&oref=article
Nadarajah, I. (1997, June 13). Bacteria Found in over Half of Cooling Tower Samples. the Strait Times. National Iron planning Malaysian joint venture. (1989, July 10). BUSINESS TIMES. Retrieved from
http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19890710-1.2.34.8?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=1989&QT=singapore,steel,production&oref=article
National Steel Mills quadruples its spending on hi-tech. (1985, May 7). Singapore Monitor. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/singmonitor19850507-2.2.15.1?ST=1&AT=filter&K=singapore+steel+production&KA=singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=&WC=&YR=1985&QT=singapore,steel,production&oref=article
Natural gas now makes up 95.5% of fuel mix; renewable energy on the rise. (2015, July 21). the Straits Times. Retrieved from https://www.straitstimes.com/singapore/from-the-straits-times-archives-singapore-opts-for-cleaner-energy-sources
Nature's defences help Singapore. (1972, April 26). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19720426-1.2.62.1?ST=1&AT=filter&K=air+pollution+control+singapore&KA=air+pollution+control+singapore&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&P=2&Display=0&filterS=0&QT=air,pollution,control,singapore&oref=article
NewspaperSG. (2019). An online archive of Singapore's newspapers. http://eresources.nlb.gov.sg/newspapers/
Nielsen, M., Nielsen, O.-K., & Hoffmann, L. (2013). Improved inventory for heavy metal emissions from stationary combustion plants: 1990-2009. Retrieved from https://dce2.au.dk/pub/SR68.pdf
Nriagu, J. O., & Nieboer, E. (1988). Chromium in the natural and human environments (Vol. 20): John Wiley & Sons.
Nriagu, J. O., & Pacyna, J. M. (1988). Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature, 333(6169), 134-139.
927928929930931932933934935936937938939940941942943944945946947948949950951952953954955956957958959960961962963964965966967968969970971972973974975976
NSL Chemicals. (2016). Refractory. Retrieved from http://www.nslchemicals.com.sg/our-business/refractory
Number of car trebles in 10 years. (1963, April 12). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19630412-1.2.104?ST=1&AT=search&k=Singapore%20number%20of%20cars&QT=singapore,number,of,cars&oref=article
Oon, S., & Saparudin, K. B. (2014). Clean Air Act of 1971. Retrieved from http://eresources.nlb.gov.sg/infopedia/articles/SIP_2014-04-07_110024.html
Pacyna, J. M., & Pacyna, E. G. (2001). An assessment of global and regional emissions of trace metals to the atmosphere from anthropogenic sources worldwide. Environmental Reviews, 9(4), 269-298.
Passant, N. R., Peirce, M., Rudd, H. J., Scott, D. W., Marlowe, I., & Watterson, J. D. (2002). UK particulate and heavy metal emissions from industrial processes. Retrieved from https://uk-air.defra.gov.uk/assets/documents/reports/empire/AEAT6270Issue2finaldraft_v2.pdf
Plans for 5th incineration plant for solid waste. (2013, September 11). The Straits Times. Retrieved from https://www.eco-business.com/news/plans-5th-incineration-plant-solid-waste/
Pollution under control here. (1989, July 16). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19890716-1.2.23.3?ST=1&AT=filter&K=air+pollution+control+singapore&KA=air+pollution+control+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=air,pollution,control,singapore&oref=article
Pulles, T., van der Gon, H. D., Appelman, W., & Verheul, M. (2012). Emission factors for heavy metals from diesel and petrol used in European vehicles. Atmospheric Environment, 61, 641-651.
Putting more rubbish to good use. (1986, June 20). Business Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19860620-1.2.11.7?ST=1&AT=filter&K=low+cost+incinerator&KA=low+cost+incinerator&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=&WC=&YR=&QT=low,cost,incinerator&oref=article
Refractory products from Jurong. (1969, November 10). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19691110-1.2.138.aspx?q=refractory&mode=advanced&ct=article&t=beritaharian%2cdailyadvertiser%2ceasterndaily%2ckabarslalu%2cmalayansatpost%2cmiddayherald%2cnewnation%2csingchronicle%2csingdailynews%2csingmonitor%2csingweekherald%2cstraitsadvocate%2cstraitschinherald%2cstraitseurasian%2cstraitsmail%2cstraitsobserver%2cstraitstelegraph%2cstoverland%2cstweekly%2cbiztimes%2cnewpaper%2cfreepress%2csingfreepressa%2csingfreepressb%2cstraitstimes%2ctoday%2cweeklysun%2cnysp%2cscjp%2clhzb%2clhwb&page=2&sort=relevance&token=refractory&sessionid=b63a3b38c407434f8fd1126387ef8ee6
Remarkable growth in the face of recession in world trade. (1974, September 26). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19740926-1.2.34.1?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,steel,production&oref=article
Samaras, Z., Ntziachristos, L., Thompson, N., Hallb, D., Westerholm, R., & Boulterd, P. (2005). Characterisation of Exhaust Particulate Emissions from Road Vehicles. Retrieved from https://tonnerimis.ec.europa.eu/sites/default/files/project/documents/20100310_132356_74824_Particulates%20Final%20Publishable%20Report.pdf
Sin, J., Tham, S., & Low, L. (2015). Jurong Heritage Trail. Singapore: National Heritage Board.Singapore's Economic Progress Remains Steady. (1933, August 24). The Straits Times. Retrieved from
http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19330824-1.2.95?
977978979980981982983984985986987988989990991992993994995996997998999
1000100110021003100410051006100710081009101010111012101310141015101610171018101910201021102210231024102510261027
ST=1&AT=filter&K=low+cost+incinerator&KA=low+cost+incinerator&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=&WC=&YR=&P=2&Display=0&filterS=0&QT=low,cost,incinerator&oref=article
Singapore's first cement works to open in April. (1961, November 3). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19611103-1.2.73.4?ST=1&AT=filter&K=Singapore+cement+production&KA=Singapore+cement+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,cement,production&oref=article
Singapore's oil pipelines. (1977, January 28). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19770128-1.2.65?ST=1&AT=filter&K=Singapore+electricity+consumption&KA=Singapore+electricity+consumption&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,electricity,consumption&oref=article
Singapore again faces a shortage of cement. (1972, January 5). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19720105-1.2.118?ST=1&AT=filter&K=Singapore+cement+production&KA=Singapore+cement+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,cement,production&oref=article
Singapore Department of Statistics. (2018a). Electricity Generation, Consumption and Tariffs 1975-2017. http://www.tablebuilder.singstat.gov.sg/publicfacing/createDataTable.action?refId=14602
Singapore Department of Statistics. (2018b). Statistics Singapore. https://www.singstat.gov.sg/Singapore may need to recycle more waste. (1989, December 5). The Straits Times. Retrieved from
http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19891205-1.2.31.10?ST=1&AT=filter&K=refuse+recycle+singapore&KA=refuse+recycle+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=refuse,recycle,singapore&oref=article
Singapore Land Transport Authority. (2019). Certificate of Entitlement (COE). Retrieved from https://www.lta.gov.sg/content/ltaweb/en/roads-and-motoring/owning-a-vehicle/vehicle-quota-system/certificate-of-entitlement-coe.html
Singapore National Environment Agency. (2017a). Tuas South Incineration Plant. Retrieved from https://www.nea.gov.sg/docs/default-source/e-services-forms-docs/forms/tonnesip-brochure.pdf
Singapore National Environment Agency. (2017b). Waste Statistics and Overall Recycling. Retrieved from http://www.nea.gov.sg/energy-waste/waste-management/waste-statistics-and-overall-recyclingSingapore National Environment Agency. (2018). Waste Statistics and Recycling Rate 2003-2017. Singapore National Environment Agency. (2019). Waste Disposed Of And Recycled, Annual.
https://data.gov.sg/dataset/waste-disposed-of-and-recycled-annual?resource_id=7918b229-0e79-4d74-b725-e34183a56c01
Singapore Pollution Control Department. (1986). Pollution Control Report 1986-2003. Retrieved from Singapore:
Singapore Public Utilities Board. (1965). Souvenir Brochure: Commemorating the opening of Pasir Panjang 'B' Power Station. Singapore.
Singapore Public Utilities Board. (1970). Jurong Power Station will be officially opened by Dr. Goh Keng Swee. Retrieved from Singapore:
Singapore Public Utilities Board. (2017). Technical Reference for Water Conservation in Cooling Towers. Retrieved from https://www.pub.gov.sg/Documents/tonneechnicalReference_WaterConservation_CoolingTowers.pdf
102810291030103110321033103410351036103710381039104010411042104310441045104610471048104910501051105210531054105510561057105810591060106110621063106410651066106710681069107010711072107310741075107610771078
Singapore Public Utilities Board. (2018). Best practice guide in water efficiency buildings, version 1. Retrieved from https://www.pub.gov.sg/Documents/PUB_Water_Efficiency_Guidebook.pdf
Smells at Government House. (1900, May 31). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19000531-1.2.50?ST=1&AT=filter&K=Singapore+incinerator&KA=Singapore+incinerator&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7cILLUSTRATION&WC=&YR=&P=2&Display=0&filterS=0&QT=singapore,incinerator&oref=article
So you think it's just a lot of rubbish. (1980, February 29). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19800229-1.2.108.11.1?ST=1&AT=filter&K=national+iron+and+steel+dust+singapore&KA=national+iron+and+steel+dust+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=national,iron,and,steel,dust,singapore&oref=article
Steel factory leads war on the smog. (1970, March 11). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19700311-1.2.59?ST=1&AT=filter&K=national+iron+and+steel+dust+singapore&KA=national+iron+and+steel+dust+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=national,iron,and,steel,dust,singapore&oref=article
Stricter measures to control pollution from brickworks. (1987, February 19). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19870219-1.2.34.9?ST=1&AT=search&k=HDB%20brickworks%20production&QT=hdb,brickworks,production&oref=article
Strong balance sheet puts NISM on firm footing. (1983, December 3). SINGAPORE MONITOR. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/singmonitor19831203-1.2.19.8?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,steel,production&oref=article
Tan, L., Choa, V., & Tay, J. (1997). The influence of pH on mobility of heavy metals from municipal solid waste incinerator fly ash. Environmental Monitoring and Assessment, 44(1-3), 275-284.
Task Ahead. (1964, January 31). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19640131-1.2.153.4?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,steel,production&oref=article
Tay, J.-H., & Goh, A. T. (1991). Engineering properties of incinerator residue. Journal of environmental engineering, 117(2), 224-235.
Tian, H., Zhu, C., Gao, J., Cheng, K., Hao, J., Wang, K., . . . Zhou, J. (2015). Quantitative assessment of atmospheric emissions of toxic heavy metals from anthropogenic sources in China: historical trend, spatial distribution, uncertainties, and control policies. Atmospheric Chemistry and Physics, 15(17), 10127-10147.
Trade Talk. (1983, June 8). Business Time. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19830608-1.2.14.6?ST=1&AT=filter&K=Singapore+cooling+tower&KA=Singapore+cooling+tower&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,cooling,tower&oref=article
United States Board of Public Works. (1995). Factsheet: Eliminating Hexavalent Chrome from Cooling Towers. Retrieved from Los Angeles: http://www.gfxtechnology.com/CR6.pdf
10791080108110821083108410851086108710881089109010911092109310941095109610971098109911001101110211031104110511061107110811091110111111121113111411151116111711181119112011211122112311241125112611271128
United States Environmental Protection Agency. (1989). Locating and Estimating Air Emissions from Sources of Chromium-Supplement (EPA-450/4-84-007G). Retrieved from https://www3.epa.gov/tonnetnchie1/le/chromium.pdf
United States Environmental Protection Agency. (1995). AP-42: Compilation of Air Emissions Factors: Refractory Manufacturing. Retrieved from https://www3.epa.gov/tonnetnchie1/ap42/ch11/final/c11s05.pdf
United States Environmental Protection Agency. (1997). Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources, fourth edition, AP-42. Section 11.3 Bricks and Related Clay products. Retrieved from https://www3.epa.gov/tonnetnchie1/ap42/ch11/final/c11s03.pdf
Veloo, R. (1992, June 7). Five in S'pore die from Legionnaires' disease. The Straits Times. World Bank. (2016). MSW Composition by Country Retrieved from
http://siteresources.worldbank.org/INTURBANDEVELOPMENT/Resources/336387-1334852610766/AnnexM.pdf
Zaccheus, M. (2014, September 26). Patching heritage cracks. The Straits Times.
112911301131113211331134113511361137113811391140114111421143
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