Air Pollution Industrial smog • A “killer smog” from Donora, Pennsylvania, in 1948, at mid-day. Subsequent demand for legislation against pollution began the process of creating laws to clean up U. S. air pollution Air Pollution - Themes: I. Natural Atmospheric Cycles & Pollutants II. Human Air Pollution A. Conventional Pollutants B. Unconventional Pollutants C. Indoor Air Pollution III. Effects of Air Pollution IV. Solutions / Clean Air Legislation I. Nature & Air Pollution • Many of the major air pollutants released by human activities are associated with natural biogeochemical cycles – for example: – Nitrogen oxides are released from soils by bacteria – Carbon monoxide is rapidly converted to CO2 and becomes part of the carbon biogeochemical cycle – Volatile organic compounds are released naturally by vegetation Natural sources of air pollution • Natural Fires - Particulates, CO • Volcanoes - Particulates, SO2, Acids • Sea Spray - Particulates, Sulfur • Vegetation - Volatile organic compounds • Bacterial Metabolism - Methane, NOx • Wind blown dust • Viruses, bacteria, spores, pollen are all particulates in the air II. Human-caused air pollution • U.S. releases ~ 150 million metric tons of air pollutants annually • Global emissions are 1 billion metric tons ? • Developed countries have been improving air quality, while LDCs have declining air quality We Describe Pollutants in Several Ways • In the U.S., principal pollutants are identified and regulated by the Clean Air Act of 1970. • A point source is a smokestack or some other concentrated pollution origin. • Primary pollutants are released in a harmful form • Secondary pollutants become hazardous after reactions in the air • Fugitive or nonpoint-source emissions are those that do not go through a smokestack Describing Pollutants Based on Source • Primary Pollutants - Released directly from a source – Sulfur Dioxide – Nitrogen Oxides (NOx) – Carbon Monoxide – Hydrocarbons – Particulates • Secondary Pollutants - Modified after entering the air and mixing with other environmental components – Photochemical Oxidants (UV light catalyst) – Industrial/Urban Smog – Acids Convential Air Pollutants • Conventional or Criteria pollutants are a group of seven major pollutants that contribute the largest volume of air-quality degradation and are considered the most serious threat of all air pollutants to human health and welfare • Transportation and power plants are the dominant sources of most of these pollutants A. Conventional Pollutants • US Clean Air Act designated 7 major conventional (criteria) pollutants for which maximum ambient air levels are mandated – Sulfur Dioxide – Nitrogen Oxides – Carbon Monoxide – Hydrocarbons (volatile organic compounds) – Particulates – Ozone & photochemical oxidants – Lead • Sulfur oxides – Natural sources: sea spray, volcanoes – Main human source is coal-fired power plants • Annual U.S. Emissions: 15 million metric tons • Nitrogen oxides – Naturally released from soils by bacteria – Main human source is fossil fuel combustion in transportation and power plants • Annual U. S. Emissions: 20 million metric tons • Carbon monoxide – Main natural source is fire – CO is produced by incomplete fuel combustion • Annual U. S. Emissions: 80 million metric tons • Hydrocarbons (VOC) – Naturally produced by plants (esp. conifers) – Human sources are from autos & industrial processes • Of 188 air toxins listed in Clean Air Act, 2/3 are VOC’s • Annual U. S. Emissions: 15 million metric tons • Particulate Matter (aerosols) – Natural sources: fires, ocean spray, soil dust – Human sources: road dust, diesel emissions, fires • Smaller particles (<2.5 micrometers) are most dangerous, and now monitored • (prior to 2006 all particles <10 µm were monitored) • Annual U. S. Emissions: 4 million metric tons • Ozone (& photochemical oxidants) – Products of secondary atmospheric reactions driven by solar energy (uv light provides energy) • Ozone is formed by splitting NO2 or CO – Some are produced directly by industry • CFCs, methyl bromide, plastics by-products A vast array of photochemical reactions lead to other secondary pollutants • Lead – Many toxic metals occur as trace elements in fossil fuel, especially coal (lead, mercury, cadmium) • Lead was added to gasoline in U. S. until 1987! • Annual U. S. Emissions: 1981: 2002: 200,000 metric tons 1,700 metric tons • A “Clean Air Act” accomplishment! Anthropogenic Sources of Criteria Air Pollutants Unconventional Pollutants • The EPA also monitors unconventional pollutants, compounds that are produced in less volume than conventional pollutants, but that are especially toxic or hazardous • Among these are asbestos, benzene, beryllium, mercury, polychlorinated biphenyls (PCBs), and vinyl chloride • In 2009, the EPA announced that it would add CO2 and other greenhouse gases to its list of regulated pollutants • This decision remains controversial Indoor Air Can Be More Dangerous Than Outdoor Air Interactions Between Climate and Air Pollution • Air pollutants can travel far: – Dust and fine aerosols can be carried great distances by the wind – Pollution from the industrial belt between the Great Lakes and the Ohio River Valley regularly contaminates the Canadian Maritime Provinces and sometimes can be traced as far as Ireland – Similarly, dust storms from China’s Gobi and Takla Makan Deserts routinely close schools, factories, and airports in Japan, and even reach Seattle in the U.S. Dust Blowing From the Sahara • Dust from North Africa regularly crosses the Atlantic and contaminates the air in Florida and the Caribbean Islands • This dust can carry pathogens and is thought to be the source of diseases attacking Caribbean corals Ozone in the Stratosphere is Harmed by CFCs • Antarctica’s exceptionally cold winter temperatures help break down ozone. • During the Antarctic spring, conditions are ideal for rapid ozone destruction. CFC Control has Been Remarkably Successful • In 1987 an international meeting in Montreal, Canada, produced the Montreal Protocol, the first of several major international agreements on phasing out most uses of CFCs by 2000 • As evidence accumulated, showing that losses were larger and more widespread than previously thought, the deadline for the elimination of all CFCs was moved up to 1996 • CFCs are now being removed from the atmosphere more rapidly than they are being added Success of the Montreal Protocol Effects of Air Pollution • Polluted air is unhealthy! – Polluted air increases probability of heart attacks, respiratory diseases, and lung cancer • Plants are sensitive to pollutants – Fumes from furnaces, smelters, refineries, and chemical plants often destroyed vegetation and created desolate, barren landscapes around mining and manufacturing centers • Synergistic effects in which the injury caused by exposure to two factors together is more than the sum of exposure to each factor individually – are thought to be causing the mortality to 9-26 forest trees east of Los Angeles Effects continued… • Smog and haze reduce visibility – Grand Canyon National Park had maximum visibility of 300 km (185 mi), but is now so smoggy on some days that visibility is only 20 km (12.5 mi) across the canyon • Acid deposition has many effects – Acid precipitation, and dry acidic particles from the air, became widely recognized as a pollution problem in the last 20 years – The most notable aquatic effects of acid deposition are the reduction of trout, salmon, and other game fish, whose eggs & juveniles die below pH 5 – Forest damage: On Mount Mitchell in North Carolina, nearly all the trees above 2,000 m (6,000 ft) are losing needles, and about half are dead Acid Precipitation Over the United States 9-28 Acid Precipitation Kills Vegetation Forest Damage by Acid Rain 9-30 Buildings and Monuments Show Clear Damage • Air pollution is destroying some of the oldest and most glorious buildings and works of art • Smoke and soot coat buildings, paintings, and textiles • Acids dissolve limestone and marble, destroying features and structures of historic buildings Air Pollution Control • Particulate removal involves filtering air emissions Filters trap particulates in a mesh, or electrostatic precipitators are used • Sulfur removal is important because sulfur oxides are among the most damaging of all air pollutants in terms of human health • Nitrogen oxides (NOx) can be reduced in both internal combustion engines and industrial boilers • Hydrocarbon controls mainly involve complete combustion or the control of evaporation Clean Air Legislation has Greatly Improved Air Quality in Developed Countries • The Air Quality Act of 1963 was the first national legislation in the United States aimed at air pollution control at the national level • In 1970, an extensive set of amendments essentially rewrote the law (= Clean Air Act) • A 2002 report concluded that simply by enforcing existing clean air legislation, the United States could save at least another 6,000 lives per year and prevent 140,000 asthma attacks Cap and Trade Agreements are One Way to Control Air Pollution • A cap-and-trade approach sets maximum emission levels for pollutants • Facilities can then buy and sell emission “credits,” or permitted allotments of pollutants • Companies can decide if it’s cheaper to install pollution control equipment or to simply buy someone else’s credits • Cap-and-trade has worked fairly well for sulfur dioxide in local regions Current Conditions and Future Prospects • Although the United States has not yet achieved the Clean Air Act goals in many parts of the country, air quality has improved dramatically • For 23 of the largest U.S. cities, the number of days each year in which air quality reached the hazardous level is down 93 percent from a decade ago • The outlook is not so encouraging in other parts of the world
