1. Visual Air Quality Big Bend National Park

2. Big 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 Bend Natl. Park

3. Big Bend – A Land of Panoramic Views South Rim View

4. Big Bend – A Land of Panoramic Views Casa Grande

5. Big Bend – A Land of Panoramic Views Juniper Canyon – The Boot

6. Big Bend – A Land of Panoramic Views Sierra Del Carmen Mountains - Mexico

7. Big Bend – A Land of Panoramic Views Chisos Basin

8. Visibility: Defining the Problem Visibility: Defining the Problem

9. Big Bend – Air Pollution Although remote, Big Bend is not immune to urban problems like air pollution.

10. Big Bend – 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.

11. Big Bend – Air Pollution On some days during the summer the park experiences the worst visibility of any western national park. On some days during the summer the park experiences the worst visibility of any western national park.

12. Clear day Hazy day Views throughout the park are impacted to some degree most of the time. It’s Hazy and Getting Hazier

13. Most visitors believe the haze is natural. It’s not. The primary cause is human activity. Clear day Hazy day It’s Hazy and Getting Hazier

14. Clear day Hazy day Noticeable changes in air quality appeared around the turn of the century in many areas of the U.S. It’s Hazy and Getting Hazier

15. Clear day Hazy day Park managers began monitoring the air at Big Bend in 1978. It’s Hazy and Getting Hazier

16. 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. It’s Hazy and Getting Hazier

17. How Far Can You See? Good Day – over 100 miles It’s this good or better 10% of the time. Good Day – over 100 miles It’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 Mountain 17 Miles

18. Visibility Concepts Visibility Concepts

19. 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.”

20. What is Visibility? 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.

21. What is Visibility? 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

22. 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 extent and distribution of particles and gases in the atmosphere. Three Types of Haze

23. 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 Haze Scattering in the Atmosphere Scattering

24. 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. How Pollutants Cause Haze Absorption in the Atmosphere Absorption

25. Extinction 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. How Pollutants Cause Haze

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

27. Microscopic Airborne Particles Examples of particles that affect visibility Particles fall into two size categories: 1. Coarse Particles greater than 2 micrometers and less than 10 micrometers (These particles usually deposit out of the air close to their source.) 2. Fine Particles 2.5 micrometers and smaller (These particles can stay suspended for weeks and are transported far from their source.)

28. 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

29. 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 from chemical reactions involving primary gas emissions (precursors), and include: 1. Ammonium Sulfate 2. Ammonium Nitrate 3. Organic compounds

30. Secondary 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.

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

32. 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/m 3 ). The relative humidity changes from 10% to 50% to 90%. Dagger Mtn. 10% RH visual range = 35 mi. Dagger Mtn. 50% RH visual range = 27 mi. Dagger Mtn. 90% RH visual range = 10 mi.

33. Sources of Visibility-Reducing Pollutants

34. Policies Aimed at Improving Visibility Policies Aimed at Improving Visibility

35. “… 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

36. “…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

37. Clean Air Act 1970 Act Established special goals for visibility in national parks, wilderness areas, and international parks. 1970 Act Established 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 Amendments Expanded the focus to include mitigating regional haze, an issue encompassing multiple sources located within multiple jurisdictions and under the purview of multiple institutions. 1990 Amendments Expanded the focus to include mitigating regional haze, an issue encompassing multiple sources located within multiple jurisdictions and under the purview of multiple institutions.

38. Addresses visibility impairment in 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 impairment in 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 Rule April 1999

39. What is the Park Doing? What is the Park Doing?

40. IMPROVE Interagency Monitoring of Protected Visual Environments 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.

41. Visibility 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.

42. Visibility Monitoring - Aerosol Aerosols 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

43. Visibility 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

44. Other Air Quality Monitoring Rainfall 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 atmosphere.

45. Monitoring Results

46. 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.

47. 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 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 )

48. 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. 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 Bend

49. Sulfate 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 SO 2 to sulfate depends on the oxidative capacity of the atmosphere which is influenced by NO x and volatile organic carbon emissions.

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

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

52. Monitoring Trends at Big Bend National Park Monitoring Trends at Big Bend National Park

53. Trends in Extinction at Big Bend from 1990–2002 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 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.

54. 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 2 nd and 3 rd quarters. Spring Peak (April-June) Fall Peak (August-October) Particle Extinction Mm-1 Amm. Sulfate CoarseSoil Organics LAC Amm. Nitrate

55. Big Bend Extinction Budget, 1998–2002 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 Sulfate Coarse Organics 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.

56. Special Study Special Study

57. BRAVO Study, July–October, 1999 B ig Bend R egional A erosol & V isibility O bservational S tudy Because sulfates are the major chemical component of visibility reducing particles, the study focused on sulfate production mechanisms and the relative contribution SO 2 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.

58. BRAVO 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 SO 2 source regions in the southeastern and midwestern U.S.

59. 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 Carbón I - Mexico Carbón II - Mexico

60. BRAVO Network Configuration Tracer Release and Monitoring Sites To track pollutants, tracers were released from specific source regions in Texas and Mexico. To track pollutants, tracers were released from specific source regions in Texas and Mexico.

61. Measurements were made at 37 sites over a 4-month period followed by 4 years of data analysis. Measurements were made at 37 sites over a 4-month period followed by 4 years of data analysis. BRAVO Network Configuration Gas and Aerosol Sampling Locations

62. 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.

63. BRAVO Emissions Inventory, U.S. / Mexico SO 2 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.

64. BRAVO Emissions By Source Region Numerous methods were used to identify source types and source regions that contribute to sulfate haze at Big Bend. SO 2 sources are defined as either elevated point sources (coal-fired power generation) or area sources (diesel combustion from mobile sources).

65. Newly Built and Proposed New Power Plants in Texas

66. Central Texas Smoke Impact Local, Regional, & International Transport Sulfate Coarse Organics Smoke and dust is a regional issue with distant sources contributing to 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 contributing to 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 layer Transport of Central American smoke in low-level moist layer

67. Models: Linking Emissions to Measured Pollutants Receptor Concentration Dilution Chemistry/ Removal Emissions = * * Source contribution to receptor concentration Source contribution to receptor 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.

68. 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. Click on map to play/stop movie

69. Simulated Tracer Release Regional 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

70. 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 SO 2 emissions facility.

71. Big Bend’s Sulfate Haze Source Attribution 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. Mexico Texas Eastern US Western US Mexico

72. 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%). Western US 2 % Contribution to Big Bend’s Haze - BRAVO 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

73. Clear Day – Pollution Free

74. Average 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.

75. Average 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.

76. What is Causing Big Bend’s Haze? Urban Activity Shipping – Harbor Activity Railroads – Diesel Emissions Refining and Industrial Manufacturing Refining and Industrial Manufacturing Power Plant Emissions – Transport from Mexico Power Plant Emissions – Transport from Mexico Power Plants – Especially Coal-Fired Plants

77. What is Causing Big Bend’s Haze? 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.

78. 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

79. 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?

80. How Can Visibility be Improved… Control SO 2 emissions from the Carbón power plants. Significantly reduce SO 2 emissions in both east Texas and the eastern U.S. Reductions in SO 2 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 SO 2 reductions within the state. As SO 2 emissions are reduced, the role of organic carbon and coarse soil in reducing visibility will become increasingly important. at Big Bend National Park?

81. 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!

82. What Can You Do? Concerned Citizens Against Pollution at Texas State Capitol, Austin, TX. Be Involved!