ASSIGNMENT NO 2 ATMOSPHERIC POLLUTION (AIR POLLUTION)

NAME ZOHA SALEEM

CLASS MSC CHEMISTRY

SEMESTER 4 th

SUBMITTED TO SIR MUSA KALEEM

QURTUBA UNIVERSITY OF SCIENCE AND INFORMATION TECHNOLOGY

Q1. Define air pollution, Discuss in detail the main sources of air pollution?

Ans.

AIR POLLUTION

Definition,

Air pollution can be defined as the presence of toxic chemicals or compounds (including those of biological origin) in the air, at levels that pose a health risk. In an even broader sense, air pollution means the presence of chemicals or compounds in the air which are usually not present and which lower the quality of the air or cause detrimental changes to the quality of life (such as the damaging of the ozone layer or causing global warming)

OR

AIR pollution can also be defined as the of one more contaminants / pollutants or combinations in such a quantities of and a such durations as may be or tend to be injurious to human and animal and plant life, or property or which unreasonably interferes with the comfortable enjoyment of life or property or conduct of business.

Sources and classification of pollutants

These pollutants / contaminants can be in form of solid particles, liquid droplets, or gases. In addition the may be natural or man-made.

Outdoor Pollution

Smog is a type of large-scale outdoor pollution. It is caused by chemical reactions between pollutants derived from different sources, primarily automobile exhaust and industrial emissions. Cities are often centers of these types of activities, and many suffer from the effects of smog, especially during the warm months of the year. Another consequence of outdoor air pollution is acid rain. When a pollutant, such as sulfuric acid combines with droplets of water in the air, the water (or snow) can become acidified. The effects of acid rain on the environment can be very serious even. It damages plants by destroying their leaves, it poisons the soil, and it changes the chemistry of lakes and streams if even if the changes are small. Damage due to acid rain kills trees and harms animals, fish, and other wildlife that are not adapted to the new acid levels.

Indoor PollutionMany people spend large portion of time indoors – as much as 80-90% of their lives. We work, study, eat, drink and sleep in enclosed environments where air circulation may be restricted. For these reasons, some experts feel that more people suffer from the effects of indoor air pollution than outdoor pollution.There are many sources of indoor air pollution. Tobacco smoke, cooking and heating appliances, and vapors from building materials, paints, furniture, etc. cause pollution inside buildings. Radon is a natural radioactive gas released from the earth, and it can be found concentrated in basements in some parts of the United States. Pollution exposure at home and work is often greater than outdoors. The California Air Resources Board estimates that indoor air pollutant levels are 25-62% greater than outside levels and can pose serious health problems.

There are four main types of air pollution sources:

mobile sources – such as cars, buses, planes, trucks, and trainsstationary sources – such as power plants, oil refineries, industrial facilities, and factoriesarea sources – such as agricultural areas, cities, and wood burning fireplacesnatural sources – such as wind-blown dust, wildfires, and volcanoes

1.Natural air pollutionAir may get polluted by natural causes such as volcanos, which release ash, dust, Sulphur and other gases, or by forest fires that are occasionally naturally caused by lighting , however, unlike pollutants form human activity, naturally occurring pollutants tend to remain in the atmosphere for a short time and do not lead to permanent atmospheric change.

SULPHUR DIOXIDE (SO2)Fossil fuel combustion (principally power stations), conversion of wood pulp to paper, manufacture of sulphuric acid, smelting, incineration of refuse. The most common natural source is volcanoes. CARBON MONOXIDE (CO)CO forms when carbon fuels are burned, either in the presence of too little oxygen or at too high a temperature. One of the main causes is idling vehicle engines and vehicle deceleration. Smaller amounts are released into the atmosphere from organic combustion in waste incineration and power station processes. Levels are highest in urban areas due to its close association with road traffic. However, in the UK levels are generally low being well below the targets set by the Government.

Ozone (O3)

Ground level ozone is a secondary pollutant; it is formed through a chemical reaction of volatile organic compounds and nitrogen dioxide in the presence of sunlight, so levels are generally higher in the summer. The highest levels tend to be found in rural areas downwind of urban areas or industrial sites.

HYDROCARBONSHydrocarbons are a group of compounds consisting of carbon and hydrogens atom. They either evaporate from fuel supplies or are remnants of fuel that did not burn completely. Hydrocarbons are washed out of the air when it rains and run into the surface water. They cause an oily film on the surface and do not cause such as the serious issue until they react to form secondary pollutants. Using higher oxygen concentration in the fuel-air mixture using valves to prevent the escape of gases, fitting of catalytic converts in automobile, are are some of the modification that can reduce the release of hydrocarbons into the atmosphere.

Burning ForestsMillions of acres of forest have been cut and burned to make way for farming. Burning trees produces most of the same pollutants as burning fossil fuels.

2. Stationary sources air pollutionIndustrial and commercial operation often emit pollutants into the air. These types of air pollution contributors, called stationary source, are generally non mobile larger, emitting sources. Examples include power generating plants, mining sites , petroleum facilities and chemical plants. Pollutants release from this category include all over the criteria pollutants along with state and federally regulated air toxic pollutants. Pollution is release from a wide verity of processes at stationary sources, but most commonly from operation such as fosil feul combustion, solvent evaporation, and raw material handling.

Stationary sources can be made up many different emission points. An emission point is the specific place or piece of equipment from which a pollutant is emitted. Air pollution are frequently emitted form smokestacks storage tanks equipment leaks process 00waste water handling/ treatment areas loading and unloading operations and process vents. Emissions from all emission points at a stationary sources of summed up and used to classify the sources as a major or minor source. A major source is one of that emits or has the potential to emit pollutants over a major source threshold . A minor source is any source which emits fewer pollutants than the major source threshold.

Mobile source of air pollution.Mobile sources include vehicles, engines and equipment, that can be categorized as either on-road mobile sources (e.g. trucks, buses, passenger cars, and motorcycles) or non-road mobile sources (e.g. locomotives, marine vessels, construction equipment, lawn, garden and snow equipment, personal recreation equipment, etc.). 

Mobile source emissions include:

1.Greenhouse gases, which contribute to climate change.

2.Volatile organic compounds (VOCs) and nitrogen oxides (NOx), which combine to form ground level ozone that triggers asthma attacks, damages lung tissue, and damages forests and crops;

2.Fine particulate matter (PM), which causes respiratory and cardiovascular damage, and leads to haze that limits visibility;3.Toxic and carcinogenic compounds such as benzene, aldehydes and butadiene; andCarbon monoxide (CO), which interferes with the delivery of oxygen to the body’s organs and tissues.

toxic and carcinogenic air pollutants are of concern because they are known or suspected of causing cancer in humans, and pose a threat even at very low levels. Diseases aggravated by air pollution include chronic sinusitis, bronchitis, asthma, and allergies. Studies show that air pollution poses significant risk of pulmonary problems in developing fetuses, young children, and older individuals, and damages the immune system in healthy adults.

Area source of air pollution.

These are small sources of air pollution which by themselves may not emit very much, but when their emissions are added together, they account for a significant portion of the total emissions of air toxics. In NATA, USEPA refers to this category as "Area and Other Sources," and includes small industrial sources that fall below the "major source" threshold (meaning that annually they emit less than 10 tons of any one HAP or 25 tons of a combination of HAPs). Area sources are often too small or too numerous to be inventoried individually. The following are grouped under area sources in NATA:

1. Industrial processes such as chromium electroplating, surface coating of cans and paper, metal parts cleaning, metal recycling, small chemical manufacturing plants, and bakeries2. Consumer products, including personal care products, household products, adhesives and sealants, automotive products, and coatings such as paints3. Residential heating and fuel use4. Pesticide use5. Gasoline stations6. Dry cleaners7. Institutional and commercial heating

Q.2 what is the mean by primary and secondary pollutants discuss these in detail with reference to their source and impact?

Ans.

Air pollution is defined as the contamination of the atmosphere by substances present at concentrations above their natural levels and capable of producing adverse effects to humans, other living organisms, and the ecosystem in general.

These substances or air pollutants include gases, liquid droplets, and solid particles. They are classified according to the source of emission into two main groups:

1. primary pollutants2. secondary pollutants.

Primary pollutantsA primary pollutant is an air pollutant emitted from a source directly into the atmosphere. The source can be either a natural process such as sandstorms and volcanic eruptions or anthropogenic (influenced by humans) such as industrial and vehicle emissions.

Examples of primary pollutants are sulfure dioxide (SO2), carbon monoxide (CO), nitrogen oxides (NOX), and particulate matter (PM).

Sulfur dioxide (SO2)Sulfur dioxide is an invisible gas with a strong odor. Its main sources are anthropogenic, resulting from the combustion of fuels and the processing of mineral ores containing sulfur. Humans and animals exposed to sulfur dioxide display severe respiratory problems. Sulfur dioxide can interact with water in the atmosphere to form harmful acid rain.

Carbon monoxide (CO)Carbon monoxide is an odorless gas emitted by the incomplete combustion of fuel. The main sources for atmospheric carbon monoxide are gasoline or diesel-powered engines and biomass burning (forest fires and biomass fuels). Carbon monoxide is very toxic and is linked to an increased risk of heart disease. Exposure to high levels of CO may lead to unconsciousness or even death.

Nitrogen oxides (NOX)Fossil fuel combustion (gasoline and diesel engines) is the main source for nitrogen oxides in urban areas, while microbial activity in the soil and agricultural practices such as the use of synthetic fertilizers are its main sources in rural areas. Exposure to nitric oxides may cause an inflammation of the respiratory tracts.

Secondary pollutants

A secondary pollutant is an air pollutant formed in the atmosphere as a result of the chemical or the physical interactions between the primary pollutants themselves or between the primary pollutants and other atmospheric components. Major examples of secondary pollutants are photochemical oxidants and secondary particulate matter and ground level ozone.

Photochemical oxidantsPhotochemical oxidants result from the photochemical reactions involving sunlight with nitrogen oxides, sulfur dioxide, or volatile organic compounds. They include acids, nitrogen dioxide, sulfur trioxide, and ozone. Ozone is considered a highly dangerous air pollutant. Exposure to ozone can cause many lung diseases such as asthma, emphysema, and bronchitis. Repeated and long exposures to ozone may even permanently scar the lung tissue.

Secondary particulate matterSecondary particles are the result of the condensation of gases, the chemical reactions involving primary particles with gases, and the coagulation of various primary particles. The main primary pollutants involved in the formation of secondary particulate matter are sulfur dioxide and nitrogen oxides.

Ground-Level OzoneOzone forms when hydrocarbons and nitrogen oxides combine in the presence of sunlight and stagnant air. It is a colorless, highly irritating gas with a sweet smell that forms just above the Earth's surface.

Burning coal, gasoline and oil in homes, motor vehicles, power plants and industries creates nitrogen oxides. Gasoline combustion, oil and gas production, wood also come from natural sources such as coniferous forests.

Ozone exposure may cause premature mortality and major health issues. It also affects vegetation, hinders crop productivity and damages synthetic materials and textiles such as cotton and polyester.

Q3. Discuss in detail the impact of various pollutants over human health?

Ans.

Effects of air pollution

Air pollution consists of chemicals or particles in the air that can harm the health of humans, animals, and plants. It also damages buildings. Pollutants in the air take many forms. They can be gases, solid particles, or liquid droplets.

Effects on humans;

1. Health Effects of Carbon Monoxide (CO):

Carbon monoxide is absorbed from the lung tissue in blood stream. Competitive bending between carbon monoxide and oxygen to haemoglobin (Hb) in red blood cells (RBC) then occur forming carboxy haemoglobin (COHb) and oxyhaemoglobin (O2Hb) respectively.

Toxic effects of CO are mainly due to its high affinity for Hb which is 240 times greater than oxygen affinity. The COHb in blood of exposed population may be between 3.0 and 5.3 per cent whereas the safe limit is less than 2 per cent.

High dose exposure of CO may affect lung tissue and may lead to acute decrement in lung functions. CO level to about 5 per cent may cause cardiovascular effect in young healthy, non smoking individuals leading to fatigue and reduced ability to work.

The recurrent episode of exertial angina increase risk of precipitating heart attack, fatal arrhythmia or myocardial damage, increased risk of sudden death with coronary ortery disease. Increased concentration of carbon monoxide also leads to stroke, head injury, artherosclerosis, hypertension, etc. High CO concentration has special effect on children and infants.

There are strong evidences of reduction in birth weight, cardio megaley, delay in behaviour development and disruption of cognitive function and sometimes even infant death syndrome. The other systematic influence of CO poisoning include effects on lever, kidney, bone, immune capacity and spleen may occur in acute CO poisoning.

2. Health Effects of Lead:

Lead particles from the ambient air can be inhaled, can settle down as dust in neighbouring area, on vegetation and water bodies and may be partly ingested. Out of the total estimated release of lead from the vehicular emission, about 50-70% is released as emission into the environment and the remaining part gets deposited. Lead is pervasive environmental poison which affects virtually every system in the body. It can damage the kidneys, the nervous system, the reproductive system and cause high blood pressure.

Children are more prone to lead pollution because they absorb lead more readily than adults. It affects the development of brain of foetuses and young children. Children exposed to lead show lack of intelligence, behavioural problems and decreased ability to concentrate. Blood lead levels as low as 10 µg/decilitre are associated with harmful effects on the learning process of the children. Elevated blood lead level can be more harmful. At extremely high level (70 µg/decilitre or higher), seizure, coma and even death can occur.

Lead in specially harmful to pregnant women and infants. Lead can be accumulated and stored in bones for decades and can be released whenever there is demand for calcium such as during pregnancy and lactation. During lactation, lead crosses placenta and is detected in breast milk. This is the major source of lead to infants which causes neurological problems in the developing child.

Not to speak of ladies, infants and children’s, even adult males are not spared by lead pollution in the air. Chronic exposure with elevated blood lead levels is associated hypertension, headache, confusion, irritability, focal motor dysfunction and insomnia.

Further higher level cause drowsiness, loss of muscular coordination, kidney damage, fatigue, apathy and susceptibility to infection and anaemia. Higher blood lead level (80 µg/decilitre or more) also leads to gastro-intestinal problems and liver damage.

3. Health Effects of Volatile Organic Compounds (VOC):

The volatile compounds have potential carcinogenic effects on human beings and are termed as air toxins. These compounds react with oxides of nitrogen in the presence of sun light and give rise to photochemical smog. This smog is a dense haze which restricts visibility. Hazy fumes cause irritation to eyes and lungs and damage plant life.

4. Health Effects of Benzene

Exposure to excessively high level of benzene may cause cancer in kidney, testis, brain, pancreas, stomach, lung, respiratory tract, bladder and uterus. The benzene acts as Leukaemogen in human beings, acting as etiologic agent of aplastic anaemia leading to acute myelogenous leukaemia. World Health Organisation (WHO) estimates a four in one million risk of leukaemia on exposure to benzene to a concentration of 1 mg/m3. Benzene has also been recognised as causing DNA damage in mammalian cells.

Prolonged exposure to even mild form of benzene may cause euphoria followed by giddiness, irregular heartbeat, headache, dizziness, nausea and unconsciousness. Breathlessness, nervous irritability and unsteadiness in walking may persist for a long time.

Acute benzene poisoning includes extensive petechial haemorrhage in the brain pleurae, pericardium, urinary tract, mucous membrane and skin. Pneumonitis and bronchitis can also be caused by direct action of benzene. The other effects of benzene are disorder of blood, harmful effect on bone marrow, anaemia and reduced ability of blood to clot, damage to immune system and reproductive and development toxicant.

It has been found that benzene is more susceptible to women than men. Benzene exposure may cause menstrual disorder and retard foetal development.

5. Health Effects of Nitrogen Dioxide (NO2)

The oxides of nitrogen are toxic gases which enter the human body during breathing. High concentration of NO2 may increase susceptibility to respiratory pathogens and also increases risk of acute respiratory diseases like bronchitis, chronic fibrosis, emphysema and bronchopneumonia. N02 exposure can cause decrement in lung functions.

6. Health Effects of Sulphur Dioxide (SO2)

Human beings chronically exposed to SO2 have higher incidence of cough, shortness of breath, bronchitis, colds of long duration and fatigue. Most of the SO2 in the atmosphere is converted to sulphate salts, which are removed by sedimentation or by washout along with precipitation thereby making rain water acidic due to sulphuric acid formation.

The most common acute exposure to SO2 at concentration > = 0.4 ppm (parts per million) is induction of asthmatics after exposure lasting only 5 minutes. Increased prevalence of cough in children with intermittent exposure to SO2 levels of 1.0 ppm is observed.

7. Particle pollutantThe size of particle pollutants is directly associated with the onset and progression of the lungs and heart diseases. Particles of smaller size reach the lower respiratory tract and thus have greater potential for causing the lungs and heart diseases. Moreover, numerous scientific data have demonstrated that fine particle pollutants cause premature death in people with heart and/or lung disease including cardiac dysrhythmias, nonfatal heart attacks, aggravated asthma, and decreased lung functions. Depending on the level of exposure, particulate pollutants may cause mild to severe illnesses. Wheezing, cough, dry mouth, and limitation in activities due to breathing problems are the most prevalent clinical symptoms of respiratory disease resulted from air pollution.

8.Ozone depletion

Ozone is a gas that is both present on the ground level and Earth’s upper atmosphere known as the stratosphere. At ground level, ozone harms human health as a pollutant. However, in the stratosphere, ozone forms a layer, which protects everyone on earth from the harmful ultra-violet rays. Thinning of the ozone layer causes more UV rays to reach earth. This will lead to serious diseases like skin cancer, and cataract.

9.Acid Rain

Acid rain is caused by a chemical reaction that begins when compounds like sulfur dioxide and nitrogen oxides are released into the air. These substances can rise very high into the atmosphere, where they mix and react with water, oxygen, and other chemicals to form more acidic pollutants, known as acid rain. Sulfur dioxide and nitrogen oxides dissolve very easily in water and can be carried very far by the wind. As a result, the two compounds can travel long distances where they become part of the rain, sleet, snow, and fog that we experience on certain days.

Human activities are the main cause of acid rain. Over the past few decades, humans have released so many different chemicals into the air that they have changed the mix of gases in the atmosphere. Power plants release the majority of sulfur dioxide and much of the nitrogen oxides when they burn fossil fuels, such as coal, to produce electricity. In addition, the exhaust from cars, trucks, and buses releases nitrogen oxides and sulfur dioxide into the air. These pollutants cause acid rain.

Q4. Suggest a methodology to clean industrial air waste?

Ans.Air pollutants are generated by nearly every facet of the industrial process, including raw material sourcing, product manufacturing, maintenance and repair services, and distribution. Consequently, there are several different types of air pollution control equipment available for air pollutants produced by both mobile and stationary sources across a wide range of industries. However, this article focuses mainly on control equipment for stationary-sourced air pollutants, such as those produced during combustion processes.

In an industrial setting, air pollution control equipment is an umbrella term referring to equipment and systems used to regulate and eliminate the emission of potentially hazardous substances—including particulate matter and gases—produced by manufacturing, process system, and research applications into the air, atmosphere, and surrounding environment. Control equipment has applications in a wide range of industries, preventing the release of chemicals, vapors, and dust and filtering and

purifying the air within the work environment. Typically, fans or blowers direct industrial exhaust and emissions into the air pollution control equipment and systems which remove or reduce air pollutants through the use of one or more of the following processes:

1. Combustion (i.e., destroying the pollutant)2. Conversion (i.e., chemically changing the pollutant to a less harmful compound)3. Collection (i.e., removing the pollutant from the waste air before its release into

the environment and atmosphere)

Some types of air pollution control equipment applied to industrial applications and which utilize one or more of the methods of air pollutant removal or reduction mentioned above include:

1. Scrubbers2. Air Filters3. Cyclones4. Electrostatic Precipitators5. Mist Collectors6. Incinerators7. Catalytic Reactors8. Biofilters

1. ScrubbersSome of the most commonly used air pollution control devices in manufacturing and processing facilities, industrial air scrubbers employ a physical process—i.e., scrubbing—which removes particulates and gases from industrial emissions, such as smokestack exhaust (in the case of exhaust air scrubbers), before they are released into the atmosphere. There are two main categories of scrubbers—dry scrubbers and wet scrubbers.

Dry ScrubbersDry scrubbers, also referred to as dry adsorption scrubbers, inject dry, neutralizing chemical agents, such as sodium bicarbonate, into the emission stream, causing the gaseous pollutants contained within to undergo a chemical reaction which either neutralizes the pollutants or converts them into innocuous substances. Once the chemical reaction concludes, filters within the scrubber chamber collect and remove the spent agents from the cleaned emission gas. In some cases, the collected agents can be washed and reused for future dry scrubbing processes, but, if not possible, the scrubbing waste must be disposed of by specialists. Typically, dry scrubbers are used to remove or counteract acid gas within industrial emissions. The chemical reactions resulting from the addition of neutralizing agents during the dry scrubbing process helps to both reduce the acidity of the emissions and remove air pollutants.

Wet ScrubbersWet scrubbers, also referred to as wet adsorption scrubbers or wet collectors, employ liquid solutions—typically water—to collect and remove water-soluble gas and particulate pollutants from industrial emissions. The wet scrubbing process either passes a gas stream through a liquid solution or injects a liquid solution into a gas stream. As the gas stream comes into contact with the liquid, the solution absorbs the pollutant removing it from the stream. The types of wet scrubbing equipment available include venturi, packed bed (or packed tower), and bubbling scrubbers.

Air FiltersAir filters are devices used to control air pollution which employ a specific type of filtration media—e.g., fabric, sintered metal, ceramic, etc.—to collect and remove dry particulates and contaminants, such as dust, pollen, microbes, chemicals, etc. from air passing through them. These devices are utilized in residential, commercial, and industrial applications to remove pollutants from exhaust air and improve the air quality within the work environment. For industrial applications, there are several types of air filters available, including HEPA filters, fabric filters, and cartridge dust collectors.

An example of a HEPA air filter mat.

Cyclones

3D rendering of a cyclone dust collector separating particulate matter from a gas stream.

Cyclones—also referred to as cyclone dust collectors—are air pollution control devices which, similarly to air filters, separate dry particulate matter from gaseous emissions. However, rather than employing filtration media, cyclones utilize centrifugal force to collect and remove particulates. As gas streams enter a cyclone, they flow along a spiral path within the cylindrical chamber. This swirling motion forces large particulates against the chamber wall, which slows their inertia, causing them to drop into the collection hopper below for further processing and disposal. The cleaned gas streams continue upward and out of the cyclone.

While cyclones are typically employed for filtration applications of particulates ≥50 μm in diameter, some models are capable of greater than 90% efficiency for particulates ≥10–20 μm in diameter. Efficiency increases or decreases depending on larger or smaller particulate diameters, respectively. Typically, additional filtration devices used to control air pollution, such as baghouses, are employed following cyclones in an air pollution control system to remove the smaller particulates not previously separated and collected from the gas stream by the cyclones.

Electrostatic PrecipitatorsElectrostatic precipitators (ESPs), like air filters and cyclones, are air pollution control devices used to collect and remove particulate matter, such as dust, from industrial emissions and exhaust. ESPs employ transformers to create high static electrical potential difference between charging electrodes and collecting plates. As gas streams pass between the two components, an electrical charge is introduced to the particulates, which attracts the particulate matter to the collecting plates. Similarly to air filters, PM accumulation is periodically removed from the collecting plates and deposited

in a collection hopper below, either through mechanically dislodging the particulates or by introducing water to clean off the particulates. ESPs which employ the latter method are known as wet ESPs. As ESPs typically have multiple collection plates, their efficiencies often exceed 99%.

A diagram illustrating the mechanism of an electrostatic precipitator.

Mist CollectorsMist collectors, also known as mist or moisture eliminator filters, are air pollution control devices which remove moisture and vapor—e.g., smoke, oil, mist, etc.—from gas streams. These devices employ fine mesh-like filters to separate liquid droplets from the gas and collect them into a separate chamber for further processing and, potentially, recovery and reuse.

Mist collectors maintain high filtration efficiencies for submicron liquid particles, with some models offering 99.9% efficiency for particles ≥0.3 μm in diameter. While mist collectors are capable of processing acidic and corrosive gas streams, they cannot handle gas streams containing large particulates, as they may cause an obstruction within the collector’s filter. They also are not used in applications which have temperatures above 120 °F.

IncineratorsIncinerators are devices which employ combustion methods to break down pollutants into non-toxic byproducts. While these devices can be used to incinerate wastes in solid, liquid, and gaseous form, they are widely employed in a variety of industrial applications to maintain air quality and regulate gas emissions by converting VOCs, hydrocarbons, and other hazardous air pollutants (HAP) into innocuous compounds, such as carbon dioxide, nitrogen, and oxygen. Typically, incinerators are succeeded by scrubbers in an air pollution control system, as the scrubbing process removes any additional compounds formed through the combustion process.

Depending on the composition of the waste product, the incineration process can be either self-sustaining or requires supplementary fuel to ensure complete combustion of the waste compounds. Additionally, some incinerator models are available with regenerative and recuperative capabilities and are suitable for both continuous and batch applications. There are several types of incinerators available, including thermal oxidizers and catalytic oxidizers.

Catalytic Reactors

Catalytic reactors, also referred to as selective catalytic reduction (SCR) systems, are air pollution control devices widely used to mitigate nitrogen oxide (NOx) emissions produced by the burning of fossil fuels in industrial applications. These devices first inject ammonia into the industrial exhaust and emissions, which reacts with the NOx compounds to produce nitrogen and oxygen. Similarly to incinerators, these devices also employ other catalysts which enable some of the remaining gaseous pollutants to undergo combustion for further processing and reduction. One common application of catalytic reactors is in modern automobiles; the three-way catalytic converter in a car’s exhaust system is used to reduce the amounts of NOx, CO, and other VOCs in the engine emissions.

While for NOx reduction and removal, SCR systems can achieve more than 90% efficiencies, for other gaseous pollutants these devices can achieve 99.99% efficiencies with lower energy requirements compared to incinerators. Despite the high efficiencies possible, SCR systems are not suitable for all gaseous pollutant reduction applications as the large amounts of catalyst required are costly, and the systems cannot process emissions and exhaust containing particulate matter.

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close-up of a catalytic converter in an automobile.

BiofiltersBiofilters are air pollution control devices which employ microorganisms, such as bacteria and fungi, to degrade and remove water-soluble compounds. Similarly to incineration devices, biofilters destroy the pollutants to reduce the amount present in industrial emissions and exhaust. However, the microorganisms in biofilters absorb and metabolize gaseous pollutants, such as VOCs and organic HAP, without generating byproducts typically produced through combustion, such as NOx and CO. These devices are capable of achieving over 98% efficiencies.