visual air quality big bend national park. big bend – a land of borders one of the largest and...

Visual Air Quality

Visual Air Quality

Big Bend National ParkBig Bend National Park

Big Bend – A Land of BordersBig Bend – A Land of Borders

One of the largest and least-visited national parks, Big Bend encompasses over 800,000 acres in southwest Texas. Situated on the northern banks of the Rio Grande it is the meeting place of nations and cultures. Three states come together at Big Bend: Texas in the United States, and Coahuila and Chihuahua in Mexico. Because of it’s unique character, Big Bend was designated a Desert Biosphere Reserve in 1976.

Big BendNatl. Park

Big Bend – A Land of Panoramic Views


South Rim View South Rim View



Casa Grande Casa Grande



Juniper Canyon – The Boot Juniper Canyon – The Boot



Sierra Del Carmen Mountains - Mexico Sierra Del Carmen Mountains - Mexico



Chisos Basin Chisos Basin

Visibility:Defining the Problem

Visibility:Defining the Problem

Big Bend – Air Pollution Big Bend – Air Pollution

Although remote, Big Bend is not immune to urban problems like air pollution.

Although remote, Big Bend is not immune to urban problems like air pollution.


On many days, haze hangs over much of Big Bend’s landscape,obscuring the panoramic views many visitors seek.

On many days, haze hangs over much of Big Bend’s landscape,obscuring the panoramic views many visitors seek.


On some days during the summer the park experiencesthe worst visibility of any western national park.

On some days during the summer the park experiencesthe worst visibility of any western national park.

Clear day

Hazy day

Views throughoutthe park are impacted to some degree most of the time.

Views throughoutthe park are impacted to some degree most of the time.

It’s Hazy and Getting Hazier It’s Hazy and Getting Hazier

Most visitors believe the haze is natural.

It’s not.

The primary cause is human activity.

Most visitors believe the haze is natural.

It’s not.

The primary cause is human activity.

Clear day

Hazy day


Clear day

Hazy day

Noticeable changes in air quality appeared around the turn of the century in many areas of the U.S.

Noticeable changes in air quality appeared around the turn of the century in many areas of the U.S.


Clear day

Hazy day

Park managers began monitoring the air atBig Bendin 1978.

Park managers began monitoring the air atBig Bendin 1978.


Clear day

Hazy day

After years of data collection and analysis, researchers are begin-ning to understand what causes the pollution contributing to the park’s visibility problem and consider the sources both near and distant.

After years of data collection and analysis, researchers are begin-ning to understand what causes the pollution contributing to the park’s visibility problem and consider the sources both near and distant.


How Far Can You See?How Far Can You See?

Good Day – over 100 milesIt’s this good or better 10% of the time.

Good Day – over 100 milesIt’s this good or better 10% of the time.

Average Day – (65 –75) miles

Most visitors will see this.

Average Day – (65 –75) miles

Most visitors will see this.

Worst Days – 35 miles It’s this bad or worse 10% of the

time.

Worst Days – 35 miles It’s this bad or worse 10% of the

time.

Dagger Mountain17 Miles

VisibilityConceptsVisibilityConcepts

What is Visibility?What is Visibility?

Visibility is historically defined as:“the farthest distance one can see a large black object against the background sky.”

Visibility is historically defined as:“the farthest distance one can see a large black object against the background sky.”


Molecules in the earth’s atmosphere scatter light, limiting the maximum distance you can see even under under natural conditions.

The scattering of light by air molecules is called “blue sky” or “Rayleigh” scattering.

Molecules in the earth’s atmosphere scatter light, limiting the maximum distance you can see even under under natural conditions.

The scattering of light by air molecules is called “blue sky” or “Rayleigh” scattering. Visual Range

The theoretical limit of visual range is 243 miles.


Visibility is more than just how far we can see. It is better described as how “well” we can see and appreciate the colors, textures, forms, and detail in distant landscape features.

Visibility is more than just how far we can see. It is better described as how “well” we can see and appreciate the colors, textures, forms, and detail in distant landscape features.

Visual Range

Uniform Haze: Pollutants are uniformly distributed from the ground to a height well above the highest terrain feature.

Plume: Pollutants are constrained in a tight elevated layer that can often be traced to a nearby source.

Layered Haze: Pollutants are often trapped near the ground beneath a temperature inversion. The top edge of the pollutant layer is visible.

Visibility Impairment: generally associated with discoloration, haziness, and loss of color and detail.

How impairment manifests itself depends upon the extentand distribution of particles and gases in the atmosphere.How impairment manifests itself depends upon the extentand distribution of particles and gases in the atmosphere.

Three Types of HazeThree Types of Haze

Particles and gases in the atmosphere can scatter or redirect image-forming light as it travels to the eye.

Through scattering, some image-forming light is removed from the view path.

In addition, extra light, sunlight, and light reflected from the clouds and ground are added to the sight path, which interferes with the ability to view the scene.

How Pollutants Cause HazeHow Pollutants Cause Haze

Scattering in the AtmosphereScattering in the Atmosphere

Scattering

Another cause of visibility impairment is absorption.

Particles and gases in the atmosphere absorb or remove image-forming light before it ever reaches the viewer’s eye.

Although significant, absorption usually is less important than scattering processes when we talk about visibility impairment.


Absorption in the AtmosphereAbsorption in the Atmosphere

Absorption

ExtinctionExtinction

Extinction is a visibility metric used to describe the combined effect of scattering and absorption. It is proportional to the total amount of light removed as light passes through the atmosphere and is related to the concentration of pollutants.


Deciview is an index of haziness that expresses changes in scene quality. It is directly related to perceived changes in visibility. As haziness increases, so does the deciview value.

A one deciview change represents a 10 percent change in extinction. Most people can perceive a one deciview change.

Parameters Describing Visual Air Quality

Parameters Describing Visual Air Quality

1. Visual Range 2. Extinction 3. Deciview1. Visual Range 2. Extinction 3. Deciview

Microscopic Airborne ParticlesMicroscopic Airborne Particles

Examples of particles that affect visibility

Examples of particles that affect visibility

Particles fall into two size categories:

1. Coarse Particles

greater than 2 micrometers and less

than10 micrometers

(These particles

usually deposit out of the air

closeto their source.)

2. Fine Particles2.5 micrometers and smaller

(These particles can stay

suspended for weeks and are transported far from their source.)

Fine particles scatter light more efficiently, and there are a lot more of them. They are most important when assessing visibility impacts.

Fine particles scatter light more efficiently, and there are a lot more of them. They are most important when assessing visibility impacts.

Particle Size Matters

Increasing the mass of coarse particles (dust) by a certain amount has little effect on visibility in this scene.Increasing the mass of fine particles (sulfur) by the same amount has a much bigger effect on visibility in the same scene.

Base Case – Clear atmosphere

Five Particle Types that Reduce Visibility

Five Particle Types that Reduce Visibility

Although particulate matter is made up of many chemical species, there are five key contributors to visibility impairment.

Primary Pollutants are emitted directly into the atmosphere, and include: 1. Sulfur Dioxide 2. Nitrogen Oxides 3. Elemental Carbon 4. Organic Compounds 5. Soil or Dust

Secondary Pollutants form fromchemical reactions involving primarygas emissions (precursors), and include:

1. Ammonium Sulfate 2. Ammonium Nitrate 3. Organic compounds

Secondary Particle FormationSecondary Particle Formation

Precursor emissions disperse in the atmosphere, convert into secondary

particles through complex atmospheric chemical reactions, then travel

long distances to deposit in remote areas far from their source.

Precursor emissions disperse in the atmosphere, convert into secondary

particles through complex atmospheric chemical reactions, then travel

long distances to deposit in remote areas far from their source.

Ammonium Sulfateforms from sulfur dioxide gas emissions. Oxidation of SO2 to sulfate can be slow, requiring 1 to 2 days to convert about half of the SO2. In the presence of mist, fog, or clouds, transformation can occur in a few hours or in several minutes.

Sulfate Formation and GrowthSulfate Formation and Growth

Nitrate particles are created in much the same way from nitrogen oxide gases. Organic particles similarly evolve from gaseous emissions of hydrocarbon gases.Nitrate particles are created in much the same way from nitrogen oxide gases.

Organic particles similarly evolve from gaseous emissions of hydrocarbon gases.

Relative Humidity Affects Visibility

Fine sulfate and nitrate particles are hygroscopic. They readily attract and absorb water molecules. Under high relative humidity conditions, they quickly grow to a size that is very efficient at scattering light.

The fine sulfur levels in all views is the same (20 g/m3). The relative humidity changes from 10% to 50% to 90%.

Dagger Mtn.10% RH

visual range = 35 mi.

Dagger Mtn.50% RH


Dagger Mtn.90% RH


Sources of Visibility-Reducing Pollutants

Sources of Visibility-Reducing Pollutants

Policies Aimed atImproving VisibilityPolicies Aimed at

Improving Visibility

“… to conserve the scenery and the natural and historic

objects and the wildlife therein and to provide for the enjoyment of the same in such manner and by such

means as will leave them unimpaired for the

enjoyment of future generations.”

“… to conserve the scenery and the natural and historic

objects and the wildlife therein and to provide for the enjoyment of the same in such manner and by such

means as will leave them unimpaired for the

enjoyment of future generations.”

National Park Service Organic Act

August 26, 1916

National Park Service Organic Act

August 26, 1916

“…lands…as necessary for recreational park

purposes...are hereby established, dedicated,

and set apart as a public park for the

benefit and enjoyment of the people.”

“…lands…as necessary for recreational park

purposes...are hereby established, dedicated,

and set apart as a public park for the

benefit and enjoyment of the people.”

Big Bend National Park Authorized by Congressional Act

June 20, 1935

Big Bend National Park Authorized by Congressional Act

June 20, 1935

Clean Air ActClean Air Act1970 Act

Established special goals for visibility in national parks, wilderness areas, and international parks.

1970 ActEstablished special goals for visibility in national parks, wilderness areas, and international parks.

1977 Amendments Set a goal to achieve natural visibility conditions:

the prevention of any future, and the remedying of any existing, visibility impairment in mandatory Class I federal areas in which impairment results from man-made air pollution.

The Amendments required the EPA to issue regulations to assure “reasonable progress” toward meeting the national goal of no human-caused emissions.

1977 Amendments Set a goal to achieve natural visibility conditions:

the prevention of any future, and the remedying of any existing, visibility impairment in mandatory Class I federal areas in which impairment results from man-made air pollution.

The Amendments required the EPA to issue regulations to assure “reasonable progress” toward meeting the national goal of no human-caused emissions.1990 AmendmentsExpanded the focus to include mitigating regional haze, an issue encompassing multiple sources located within multiple jurisdictions and under the purview of multiple institutions.

1990 AmendmentsExpanded the focus to include mitigating regional haze, an issue encompassing multiple sources located within multiple jurisdictions and under the purview of multiple institutions.

Addresses visibility impairmentin the form of “regional haze”

The rule calls for states to work together to improve visibility in all mandatory Class I national parks and wilderness areas. States are encouraged to work together in regional partnerships to develop and implement multi-state strategies to reduce emissions of visibility-impairing fine particle pollution.

Additionally, states must determine whether or how much emissions from sources in a given area affect visibility in a downwind Class I area.

Addresses visibility impairmentin the form of “regional haze”

The rule calls for states to work together to improve visibility in all mandatory Class I national parks and wilderness areas. States are encouraged to work together in regional partnerships to develop and implement multi-state strategies to reduce emissions of visibility-impairing fine particle pollution.

Additionally, states must determine whether or how much emissions from sources in a given area affect visibility in a downwind Class I area.

Regional Haze RuleApril 1999

Regional Haze RuleApril 1999

What is thePark Doing?What is thePark Doing?

IMPROVE IMPROVE

Interagency Monitoring of Protected Visual Environments

Interagency Monitoring of Protected Visual Environments

Big Bend has been part of the IMPROVE national monitoring program since 1981.

Big Bend has been part of the IMPROVE national monitoring program since 1981.

The park’s goal is to develop a sound visibility database in order to establish current visibility levels, examine trends, and compare visibility at Big Bend to other remote areas of the United States.

Visibility Monitoring - OpticalVisibility Monitoring - Optical

Transmissometers measure extinction.

Nephelometers measure

scattering.

Transmissometers and nephelometers are used to record the optical characteristics of the atmosphere – measuring the amount of light transmitted over a specific viewing path.

Visibility Monitoring - AerosolVisibility Monitoring - AerosolAerosols are microscopic solid and liquid particles suspended in the air. Measurements of these particles help to identify which particles are reducing visibility.

Particles are collected on filters in various size ranges. A profile of particle types, sizes, and concentrations can be obtained.

IMPROVE fine particle monitor

Visibility Monitoring - ViewVisibility Monitoring - View

Photography documents the changing appearance of a scene as visibility levels vary,documenting changes in haze levels, lighting conditions, vegetative cover, & cloud effects.

Photography documents the changing appearance of a scene as visibility levels vary,documenting changes in haze levels, lighting conditions, vegetative cover, & cloud effects.

Big Bend operated a 35 mm camera from 1981–1985. Photographs were taken 3 times a day. 8 mm time-lapse movies recorded dynamic scene changes for several years.

Big Bend now operates two web cameras that transmit data and live pictures of current visibility conditions to the web. The view of the Sierra Del Carmens updates every 15 minutes, while the view from the Chisos Basin updates every 30 minutes. View the website at:

www2.nature.nps.gov/air/webcams/parks/bibecam/bibecam.htm

Other Air Quality MonitoringOther Air Quality MonitoringRainfall chemistry analysis began in 1980 and is part of a nationwide system that monitors changes in chemistry and acid content of precipitation.

Ozone is measured in the atmosphere on a

continuous basis.

A UV spectrophotometer measures UVB radiation to assess the effects of environmental stressors on ecological systems.

A dry deposition monitor measures nitrates, sulfates, ammonium, sulfur dioxide,

and nitric acid in

the atmosphe

re.

Monitoring Results

Monitoring Results

National Visibility Trends, 1990–1999

National Visibility Trends, 1990–1999

Over a 10-year period most parks show some improvement in average haze levels on the clearest days. Big Bend is one of three parks that shows continued degradation on these days.

20% Clearest Days -- Best Visibility Conditions

20% Haziest Days -- Worst Visibility Conditions

Most parks show some degradation (or worsening) of visual conditions on hazy days over the same period. Note that visibility degradation in the southwest is particularly significant and that Big Bend is one of three parks where haze is getting worse.

Annual Aerosol Extinction, 1996–1998

Annual Aerosol Extinction, 1996–1998

Extinction is proportional to image-forming light lost over a unit of distance.

Higher light extinction levels correspond to hazier conditions.

Extinction is proportional to image-forming light lost over a unit of distance.

Higher light extinction levels correspond to hazier conditions.

Big Bend

Inner Mountain

West

Inner Mountain

West

Big Bend has some of the worst haze in the western United States.

Compare: Big Bend(28 Mm-1)

To: Inner Mountain West (15 Mm-

1)

Fine Mass Fine Mass

Particulate matter observed during BRAVO and supported by long-term IMPROVE monitoring indicates that visibility is dominated by fine particles, but at times there are significant contributions from coarse dust particles.

Particulate matter observed during BRAVO and supported by long-term IMPROVE monitoring indicates that visibility is dominated by fine particles, but at times there are significant contributions from coarse dust particles.

Fine particles sampled at Big Bend consist mainly of ammoniated sulfate and organic carbon with black carbon, soil dust, and nitrate

particles as minor factors.

Fine particles sampled at Big Bend consist mainly of ammoniated sulfate and organic carbon with black carbon, soil dust, and nitrate

particles as minor factors.

Big Ben

d

Sulfate Mass Sulfate Mass

Sulfate Fraction of Fine Mass

Sulfate Fraction of Fine Mass

On an annual average, sulfates account for between 40 and 50% of the fine mass at Big Bend.

Sulfate compounds result from direct emissions of sulfur dioxide and generally contribute more to haze than any other individual pollutant. The oxidation of SO2 to sulfate depends on the oxidative capacity of the atmosphere which is influenced by NOx and volatile organic carbon emissions.

Organic Mass Organic Mass

Carbonaceous particles, organic compounds, and light-absorbing carbon (LAC) generally constitute the second largest individual component contributing to haze at Big Bend.

Carbonaceous particles, organic compounds, and light-absorbing carbon (LAC) generally constitute the second largest individual component contributing to haze at Big Bend.

Organic Fraction of Fine Mass

Organic Fraction of Fine Mass

On an annual average organics constitute 20–30% of the fine particles creating Big Bend haze.

On an annual average organics constitute 20–30% of the fine particles creating Big Bend haze.

Soil MassSoil Mass Soil Fraction of Fine Mass

Soil Fraction of Fine Mass

Dust – a combination of fine soil and coarse mass – contributes significantly to haze during the springtime months of March and April. Dust is transported from both local and international sources.

Dust – a combination of fine soil and coarse mass – contributes significantly to haze during the springtime months of March and April. Dust is transported from both local and international sources.

On an annual average dust contributes about 20–30% to haze-causing particles at Big Bend.

Monitoring Trendsat Big Bend

National Park

Monitoring Trendsat Big Bend

National Park

Trends in Extinctionat Big Bend from 1990–

2002

Trends in Extinctionat Big Bend from 1990–

2002

16 1/Mm / 10 yr

4.3 1/Mm /10 yr

Insignificant

0

10

20

30

40

50

60

70

90 92 94 96 98 00 02Year

Part

icu

late

Bext

(1/M

m)

Worst haze days

visibility 37–47 mi.

Average haze days visibility

65–69 mi.

Clearest days visibility 91–118

mi.

Trends in Sulfur Dioxide Emissions and Measured

Sulfate

Trends in Sulfur Dioxide Emissions and Measured

Sulfate

Sulfate concentrations and sulfur dioxide emission trends closely track each other. Emission rates in Texas and bordering states show significantly increasing trends. Between 1991 and 1999 there was a steady increase in sulfate of about 15% and a corresponding 15% increase in sulfur dioxide emissions over the region. Big Bend data shows a 37% increasing trend in measured sulfates. It is one of the few parks where both sulfates and haze are increasing.

The open symbols are annual values and the closed symbols are a 5-year moving average. The number of very hazy days has steadily increased over the last decade and the bad days are getting worse.

Big Bend sulfate compounds contribute more to haze than any other component. Carbonaceous matter (organic compounds and light-absorbing carbon (LAC)) constitute the second largest component of haze.

Information from other studies shows that biomass burning in Mexico and Central America contributes to carbonaceous matter in late spring. Dust (a combination of fine soil and coarse mass) contributes significantly to haze during March and April.

Big Bend Extinction Budget, 1998–2002


(Mm-1)

There are two periods of high haze at Big Bend National Park: spring (when sulfate and carbonaceous compounds contribute similar amounts to haze), and late summer/fall (when particulate sulfate compounds are the largest contributors to haze). 63% of the haziest days occur in the 2nd and 3rd quarters.

There are two periods of high haze at Big Bend National Park: spring (when sulfate and carbonaceous compounds contribute similar amounts to haze), and late summer/fall (when particulate sulfate compounds are the largest contributors to haze). 63% of the haziest days occur in the 2nd and 3rd quarters.

Spring Peak (April-June)

Fall Peak (August-October)

Partic

le E

xtin

ctio

n

Mm

-1

Amm.

Sulfate Coars

e Soil Organic

s LACAmm.

Nitrate



Sulfate is the single largest contributor to haze at Big Bend. Particulate sulfate contributes more to extinction on the haziest

days than on average days.

Sulfate is the single largest contributor to haze at Big Bend. Particulate sulfate contributes more to extinction on the haziest

days than on average days.

1/5 haziest Days

Ext = 54.4 Mm-1

53%

4%

18%

5%

5%

15%

Sulfate

Coarse

Organics 48%

5%18%

6%

6%

17%

All Days

Ext = 28.8 Mm-1

Sulfate

Coarse

Organics

Fine particles sampled in the Big Bend NP region are mainly ammoniated sulfate and organic carbon with black carbon, soil dust, and nitrates forming minor contributions. Coarse particles appear to be mainly soil dust.

Fine particles sampled in the Big Bend NP region are mainly ammoniated sulfate and organic carbon with black carbon, soil dust, and nitrates forming minor contributions. Coarse particles appear to be mainly soil dust.

Special Study

Special Study

BRAVO Study, July–October, 1999BRAVO Study, July–October, 1999

Big Bend

Regional

Aerosol &

Visibility Observational Study

Because sulfates are the major chemical component of visibility reducing particles, the study focused on sulfate production mechanisms and the relative contribution SO2 sources to visibility impairment in Big Bend National Park. It should be acknowledged that organic carbon and coarse particles also play a role in visibility reduction.

BRAVO Study ObjectivesBRAVO Study Objectives• Understand the long-range trans-boundary transport

of haze from regional sources in the U.S. and Mexico

– Determine the role of meteorology on Big Bend haze – Identify the most likely pollutant transport corridors

associated with Big Bend haze

• Quantify (model) the contribution of specific U.S. and Mexican source regions and source types responsible for Big Bend’s haze

– Mexican Carbón I/II power plants– Industrial source areas on the Texas gulf coast and in

Monterrey and Tula, Mexico– Coal-fired power plants and refineries in Texas (Lignite Belt)– Large SO2 source regions in the southeastern and

midwestern U.S.

Potential Source Areas of Haze at Big Bend

Potential Source Areas of Haze at Big Bend

A terrain map of Texas and Mexico showing some major cites and potential source areas of haze that could be contributing to haze

at Big Bend National Park

A terrain map of Texas and Mexico showing some major cites and potential source areas of haze that could be contributing to haze

at Big Bend National Park

Carbón I - Mexico

Carbón II - Mexico

BRAVO Network Configuration Tracer Release and Monitoring Sites

BRAVO Network Configuration Tracer Release and Monitoring Sites

To track pollutants, tracers were released fromspecific source regions in Texas and Mexico.

To track pollutants, tracers were released fromspecific source regions in Texas and Mexico.

Measurements were made at 37 sites over a 4-monthperiod followed by 4 years of data analysis.

Measurements were made at 37 sites over a 4-monthperiod followed by 4 years of data analysis.

BRAVO Network Configuration Gas and Aerosol Sampling Locations

BRAVO Network Configuration Gas and Aerosol Sampling Locations

BRAVO Study Site at KBar BRAVO Study Site at KBar

Measurements were made of speciated fine particles, gases,light scattering and absorption, particle size distributions,

meteorological parameters, and tracer concentrations.

Measurements were made of speciated fine particles, gases,light scattering and absorption, particle size distributions,

meteorological parameters, and tracer concentrations.

BRAVO Emissions Inventory, U.S. / Mexico

BRAVO Emissions Inventory, U.S. / Mexico

SO2 sources include power plants along the Ohio River Valley in the eastern U.S. and eastern Texas. Sources in Texas include coal-fired power plants, oil refineries, and carbon black producers. More power plants are located near a lignite belt running from northeast Texas towards the Mexican state of Coahuila. There are also several large point sources in northern Mexico (250 km from the park), including coal-fired power plants, fuel oil refining and combustion operations. The Carbón I &II power plants, near the U.S.-Mexico border, are the largest coal combustion facilities in Mexico.

BRAVO Emissions By Source Region

Numerous methods were used to identify source types and source regions that contribute to sulfate haze at Big Bend. SO2 sources are defined as either elevated point sources (coal-fired power generation) or area sources (diesel combustion from mobile sources).

ALLEMISSIONS EASTERN

US MEXICOTEXAS

WESTERNUS

area

point

total

1.9E+07

1.4E+07

2.5E+06

1.0E+06 1.8E+06

1.5E+07

1.2E+07

1.7E+06

9.2E+051.2E+06

4.0E+06

2.5E+06

8.5E+05

1.3E+055.1E+05

0.0E+00

2.0E+06

4.0E+06

6.0E+06

8.0E+06

1.0E+07

1.2E+07

1.4E+07

1.6E+07

1.8E+07

2.0E+07

SO

2 E

mis

sio

ns

[M

g/y

r]

Region

areapointtotal

Newly Built and ProposedNew Power Plants in Texas

Central Texas Smoke Impact

Local, Regional, & International Transport

Local, Regional, & International Transport

Sulfate Coarse

Organics

Smoke and dust is a regional issue with distant sources contributingto the haze in Big Bend. Pollutants generally remain in the air for

3 to 7 days and can be carried thousands of kilometers by the winds.

Smoke and dust is a regional issue with distant sources contributingto the haze in Big Bend. Pollutants generally remain in the air for

3 to 7 days and can be carried thousands of kilometers by the winds.

A large dust storm on April 6–7, 2001, then swept across East Asia, the Pacific, and North America

Asian Dust Plume

NAAPS Simulation of

Los Alamos Smoke Plume, May 12,

2001

Transport of Los Alamos smoke in elevated dry layerTransport of Central American smoke in low-level moist layer

Models: Linking Emissions to Measured Pollutants

Models: Linking Emissions to Measured Pollutants

ReceptorConcentration Dilution

Chemistry/Removal Emissions= * *

Source contribution toreceptor concentrationSource contribution toreceptor concentration

Source models start with known emissions and try to predict where pollutants will go and how they will change during the journey to a park (or receptor). Receptor models venture backward in time by measuring pollutants at the receptor and simulating the path the air mass took to get there.

Pollutants are emitted from a source, transformed in the atmosphere, and transported with the winds. Along the way they become diluted

or may deposit out as dry particles, or in rain, fog, or snow.

Pollutants are emitted from a source, transformed in the atmosphere, and transported with the winds. Along the way they become diluted

or may deposit out as dry particles, or in rain, fog, or snow.

Models: Transport Pathways Models: Transport Pathways

(Mm-1)

Computer models used National Weather Service wind data to look at airflows over North America on days preceding high sulfur

episodes at Big Bend National Park.

Computer models used National Weather Service wind data to look at airflows over North America on days preceding high sulfur

episodes at Big Bend National Park.

Click on map to play/stop movie

Simulated Tracer ReleaseSimulated Tracer ReleaseRegional transport results in the mixing of emissions from distant sources which can be more than 1000 km apart. The highest concentrations from a single source region often occur under stagnant winds which allow the emissions to accumulate near the sources. Re-circulating transport patterns and flow reversals also allow for the accumulation and mixing of emissions from multiple source regions. Pollutants can then be transported to downwind receptor sites, resulting in elevated pollutant concentrations.

This animation illustrates the transport and diffusion of plumes from four Texas source regions. This event demonstrates how southerly flow transports the plumes north, mixing them together. The flow reverses, passing over the sources again and allowing the pollutants to accumulate. The pollutants are then transported to Big Bend National Park.

Click on map to play/stop

movie

Big Bend NP

Modeled Big Bend Source Attribution

Modeled Big Bend Source Attribution

The sulfur oxide sources of influence on visibility at Big Bend NP are highly variable during the year. The BRAVO study found that under easterly wind conditions the eastern U.S. and sources along the northeastern border of Mexico often contribute to haze. Texas also contributes part of the time, and the Carbons’ contributions were larger than any other single SO2 emissions facility.

0

20

40

60

80

100

July 9 August 9 September 9 October 9

To

tal

Ha

ze A

ttri

bu

tio

n (

1/M

m)

Carbón Other MexicoTexas Eastern USWestern US OtherRayleigh

Organics + LAC + Nitrates +Fine Soil + Coarse

Sulfate Haze Source Attribution

Big Bend’s Sulfate Haze Source Attribution

Big Bend’s Sulfate Haze Source Attribution

0%10%20%30%40%50%60%70%80%90%

100%

July 9 August 9 September 9 October 9

To

tal

Ha

ze A

ttri

bu

tio

n

Rayleigh Scatter: Haze due to scattering by pollutant-free air

Mexico’s contribution to Big Bend sulfate was relatively high during times when average sulfate concentrations were lower than average.

The Texas and eastern U.S. sources tended to contribute to Big Bend during the highest sulfate concentrations.

Low sulfate days were dominated by contributions from Mexico in July-Sept.

At the end of Sept. and Oct., the western U.S. was also a major contributor on low sulfate days.

MexicoMexico

TexasTexas

Eastern US

Eastern US

Western USWestern USMexicoMexico

•Sulfate contributes 21% of the haze on clear days (Mexico: 10%, U.S.: 8%).

•Sulfate contributes 47% of the haze on hazy days (Mexico: 14%, U.S.: 31%).

WesternUS 2 %

Contribution to Big Bend’s Haze - BRAVO

Contribution to Big Bend’s Haze - BRAVO

Carbón4 (8)%

Other3 (5)%

Non-Sulfate Haze

32 (61)%

Western US 3 (6)%

Other Mexico6 (11)%

Texas2 (4)%

Eastern US 3 (5)%

Clear Air48%

1/5 Least Hazy BRAVO Days

Sulfate Haze21 (39)%

Average Bext = 20 1/Mm

Eastern US 19 (22)%

Texas10 (11)%

Other Mexico6 (7)% Western

US 3 (4)%

Non-SulfateHaze

38 (45)%

Other2 (3)%

Carbón8 (9)%

Clear Air15%

1/5 Haziest BRAVO Days



The relative contributions to light extinction by eastern U.S. and Texas sources of particulate sulfate at Big Bend increase by factors of about 4 and 5, respectively, on the haziest days

compared to the least hazy days of the study period.

The relative contributions to light extinction by eastern U.S. and Texas sources of particulate sulfate at Big Bend increase by factors of about 4 and 5, respectively, on the haziest days

compared to the least hazy days of the study period.

Percent contributions to particulate haze are in parentheses

Clear Day – Pollution FreeClear Day – Pollution Free

Average Low Haze Day - BRAVOAverage Low Haze Day - BRAVO

On average low haze days, sulfates contribute 22% of the haze.Mexican sources contribute about half the measured sulfates. On average low haze days, sulfates contribute 22% of the haze.Mexican sources contribute about half the measured sulfates.

Carbón4 (8)%

Other3 (5)%

Non-Sulfate Haze

32 (61)%

Western US 3 (6)%

Other Mexico6 (11)%

Texas2 (4)%

Eastern US 3 (5)%

Clear Air48%

1/5 Least Hazy BRAVO Days



Average High Haze Day - BRAVOAverage High Haze Day - BRAVO

On average high haze days, sulfates again contribute 44% of the haze. Sources in Mexico and the eastern U.S. are the largest

contributors to sulfates at Big Bend NP.

On average high haze days, sulfates again contribute 44% of the haze. Sources in Mexico and the eastern U.S. are the largest

contributors to sulfates at Big Bend NP.

Eastern US 19 (22)%

Texas10 (11)%

Other Mexico6 (7)% Western

US 3 (4)%

Non-SulfateHaze

38 (45)%

Other2 (3)%

Carbón8 (9)%

Clear Air15%

1/5 Haziest BRAVO Days



What is Causing Big Bend’s Haze?


Urban ActivityUrban ActivityShipping – Harbor Activity

Shipping – Harbor Activity

Railroads – Diesel Emissions

Railroads – Diesel Emissions

Refining andIndustrial ManufacturingRefining andIndustrial Manufacturing

Power Plant Emissions –Transport from Mexico

Power Plant Emissions –Transport from Mexico

Power Plants – Especially Coal-Fired Plants

Power Plants – Especially Coal-Fired Plants



• Sulfate is the single largest contributor to haze at Big Bend NP.

• Big Bend is one of the only national parks where sulfates are increasing.

• Some of the highest haze episodes during the spring season are caused by international transport of dust and smoke.

Common Transport Pathways...Common Transport Pathways...• Throughout the year air masses en route to Big Bend

frequently reside over Mexico, particularly northern Mexico.

• Airflow from eastern Texas and the eastern U.S. is most frequent during late summer and fall months, during the period with the greatest contribution to haze by sulfate particles.

• Airflow from the western U.S. to Big Bend is greatest in the winter months when haze levels at the park are lowest.

• The highest sulfate haze periods during BRAVO were associated with low speed and low level transport from the the eastern U.S., eastern Texas, and northeastern Mexico.

• The lowest sulfate haze periods during BRAVO were associated with higher speed transport from the Gulf of Mexico up along the Mexican/Texas border to Big Bend and from the western U.S.

that Bring Pollutants to Big Bend Natl. Park

that Bring Pollutants to Big Bend Natl. Park

Where Does the Sulfate Haze Come From…

Where Does the Sulfate Haze Come From…

• At any given time, over half of the sulfate haze can come from either the eastern U.S., eastern Texas, or Mexico.

• During the BRAVO study period, the eastern U.S. and eastern Texas are responsible for ~50% on average and more on the high sulfate days of Big Bend’s sulfate haze during the BRAVO study period.

• At 20%, the Carbón power plant is the single largest contributor to Big Bend’s sulfate haze, during the BRAVO study period.

• On the clear days, Mexico and the western U.S. are the largest contributors.

at Big Bend National Park?at Big Bend National Park?

How Can Visibility be Improved… How Can Visibility be Improved… • Control SO2 emissions from the Carbón power plants.

• Significantly reduce SO2 emissions in both east Texas and the eastern U.S.

• Reductions in SO2 emissions in northern Mexico and the western U.S. can significantly improve Big Bend’s clear days.

• To address the U.S. regional haze rule, Texas will need to seek agreements for sulfur oxide reductions regionally within the U.S. and with Mexico in addition to achieving SO2 reductions within the state. As SO2

emissions are reduced, the role of organic carbon and coarse soil in reducing visibility will become increasingly important.

at Big Bend National Park?at Big Bend National Park?

What Can You Do?What Can You Do?• Stay informed about air quality issues that may affect the

park.

• Let federal, state, and local government officials know that air quality is important to you. Support ballot measures and candidates sensitive to air quality issues.

• Learn about local efforts to see what is being done in your area.

• During your visit to Big Bend, join a ranger for a guided walk or evening presentation to learn more about other issues affecting park resources.

• Conserve energy at home and at work. Use energy efficient appliances and lighting when possible. Ask your utility company about its customer energy conservation program

• Keep your car engine tuned and maintain the correct tire pressure. Use an energy-conserving grade motor oil and “clean” fuels. Drive at a medium speed; most cars operate most efficiently between 35–55 miles per hour.

Be Involved!Be Involved!

What Can You Do?What Can You Do?Concerned Citizens Against Pollution at Texas

State Capitol, Austin, TX.

Be Involved!Be Involved!

visual air quality big bend national park. big bend – a land of borders one of the largest and...

Documents

hazier slide

big bend air pollution

problem slide

boot slide

clear day hazy day views

good day

average day

worst visibility