Air Pollution 1
Outline • • Natural Sources Human-Caused Air Pollution v Conventional Pollutants v Unconventional Pollutants v Indoor Air Pollution Climate and Topography Effects of Air Pollution Control Clean Air Legislation Current Conditions and Future Prospects 2
THE AIR AROUND US • • Approximately 147 million metric tons of air pollution are released annually into the atmosphere in the U. S. by human activities. v Worldwide emissions total around 2 billion metric tons. Developed countries have been improving air quality, while air quality in developing world is getting worse. 3
NATURAL SOURCES OF AIR POLLUTION • • Natural Fires - Smoke Volcanoes - Ash and acidic components Sea Spray - Sulfur Vegetation - Volatile organic compounds Bacterial Metabolism - Methane Dust v Pollen Viruses and Bacteria 4
HUMAN-CAUSED AIR POLLUTION • • Primary Pollutants - Released directly from the source. Secondary Pollutants - Modified to a hazardous form after entering the air and mixing with other environmental components. v Fugitive Emissions - Do not go through smokestack. - Dust from human-activities. 5
Conventional Pollutants • U. S. Clean Air Act designated seven major (conventional or criteria) pollutants for which maximum ambient air levels are mandated. v Sulfur Dioxide v Nitrogen Oxides v Carbon Monoxide v Particulate Matter v Hydrocarbons v Photochemical Oxidants v Lead 6
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Conventional Pollutants • Sulfur Compounds v Natural sources of sulfur in the atmosphere include evaporation from sea spray, volcanic fumes, and organic compounds. v Predominant form of anthropogenic sulfur is sulfur-dioxide from fossil-fuel combustion. - Annual Emissions: 114 million metric tons 8
Conventional Pollutants • Nitrogen Compounds v Nitrogen oxides are reactive gases formed when nitrogen is heated above 650 o C in the presence of oxygen, or when nitrogen compounds are oxidized. - Annual Emissions: 230 million metric tons 9
Conventional Pollutants • Carbon Oxides v Predominant form of carbon in the air is carbon dioxide. - Increasing levels due to human activities. - Annual Emissions: 7 -8 billion metric tons v Carbon monoxide is a colorless, odorless, toxic gas produced by incomplete fuel combustion. - Annual Emissions: 1 billion metric tons 10
Conventional Pollutants • Particulate Matter v Atmospheric aerosols (solid or liquid) - Respirable particles smaller than 2. 5 micrometers are among most dangerous. v Anthropogenic particulate emissions amount to about 362 million metric tons annually. v Desertification and dust storms v Effect of particulates on human health 11
Conventional Pollutants • • Metals v Many toxic metals occur as trace elements in fuel. - Lead Emissions: 2 million metric tons. v Mercury - Dangerous neurotoxin - Widespread; control is highly contentious. v Nickel, beryllium, cadmium, arsenic… Halogens (Fluorine, Chlorine, Bromine) v CFC’s 12
Conventional Pollutants • • Volatile Organic Compounds v Organic chemicals - Generally oxidized to CO and CO 2. - Plants are largest source. Photochemical Oxidants v Products of secondary atmospheric reactions driven by solar energy. - Ozone formed by splitting nitrogen dioxide. 13
Air Toxins • Hazardous Air Pollutants v Require special reporting and management as they remain in ecosystems for a long period of time, and tend to accumulate in animal tissues. v Toxic Release Inventory - Established 1986 14
Unconventional Pollutants • Aesthetic Degradation v Noise, odor, light pollution. - Reduce quality of life. 15
Indoor Air Pollution • EPA found indoor concentrations of toxic air pollutants are often higher than outdoor. v People generally spend more time indoors. v Smoking is the most important air pollutant in the U. S. . - 400, 000 die annually from a disease related to smoking. Ø Associated costs are estimated at $100 billion annually. 16
Indoor Air Pollution • Less Developed Countries also suffer from indoor air pollution. v Organic fuels make up majority of household energy. - Often burned in smoky, poorly ventilated heating and cooking fires. 17
CLIMATE AND TOPOGRAPHY • Inversions v Temperature inversions occur when a stable layer of warm air overlays cooler air, reversing the normal temperature decline with increasing height, and preventing convection currents from dispersing pollutants. - Cold front slides under warm air mass. - Cool air subsides down slope. Ø Rapid nighttime cooling in a basin. 18
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Dust Domes and Heat Islands • Sparse vegetation and large amounts of concrete and glass create warm, stable air masses, heat islands, over large cities. v Concentrates pollutants in a “dust dome”. - Rural areas downwind from major industrial areas often have significantly decreased visibility and increased rainfall. 20
Long-Range Transport • Fine aerosols can be carried great distances by the wind. v Increasingly, sensitive monitoring equipment has begun to reveal industrial contaminants in places usually considered among the cleanest in the world. - Contaminants trapped by winds at the north pole, concentrate at high latitudes and eventually fall out as snow and ice and enter the food chain. 21
Long-Range Transport 22
Stratospheric Ozone • • Discovered in 1985 that stratospheric ozone levels were dropping rapidly during September and October. v Occurring since at least 1960. At ground-level, ozone is a pollutant, but in the stratosphere it screens UV radiation. v A 1% decrease in ozone could result in a million extra human skin cancers per year worldwide. 23
Ozone Depletion 24
Stratospheric Ozone • Circumpolar vortex isolates Antarctic air and allows stratospheric temperatures to drop and create ice crystals at high altitudes. v Absorb ozone and chlorine molecules. - When sun returns in the spring, energy liberates the chlorine allowing the depletion process to proceed rapidly. Ø CFCs believed to be main culprit. § Persist for decades. § Montreal Protocol established deadlines for eliminating CFC’s. 25
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EFFECTS OF AIR POLLUTION • Human Health v WHO estimates each year 5 -6 million people die prematurely from illnesses related to air pollution. - Likelihood of suffering ill health is related to intensity and duration of exposure. Ø Inhalation is the most common route, but absorption through the skin and consumption via food can also occur. 27
Human Health • Bronchitis v Persistent inflammation of airways in the lung that causes mucus build-up and muscle spasms constricting airways. - Can lead to emphysema - irreversible chronic obstructive lung disease in which airways become permanently constricted and alveoli are damaged or destroyed. 28
Plant Pathology • Chemical pollutants can directly damage plants, or can cause indirect damage by disrupting normal growth and development patterns. v Certain environmental factors have synergistic effects in which the injury caused by the combination is more than the sum of the individual exposures. - Pollutant levels too low to cause visible effects may still be damaging. 29
Acid Deposition • p. H and Atmospheric Acidity v Unpolluted rain generally has ph of 5. 6. - Carbonic acid from atmospheric CO 2. Ø In industrialized areas, anthropogenic acids in the air often outweigh natural sources of acid. 30
Acid Precipitation 31
Acid Deposition • Aquatic Effects v Thin, acidic soils and oligotrophic lakes of southern Norway and Sweden have been severely affected by acid deposition. - Generally, reproduction is the most sensitive stage in fish life cycles. Ø In early 1970’s, evidence began to accumulate suggesting air pollutants are acidifying many N. A. lakes. 32
Acid Deposition • • Forest Damage v Air pollution and depositions of atmospheric acids are believed to be important causes of forest destruction in many areas. Buildings and Monuments v Limestone and marble are destroyed by air pollution at an alarming rate. v Corroding steel in reinforced concrete weakens buildings, roads, and bridges. 33
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AIR POLLUTION CONTROL • Reducing Production v Particulate Removal - Remove particles physically by trapping them in a porous mesh which allows air to pass through but holds back solids. - Electrostatic Precipitators - Fly ash particles pick up electrostatic charge as they pass between large electrodes in waste stream, and accumulate on collecting plate. 35
AIR POLLUTION CONTROL • Reducing Production v Particulate Removal - Remove particles physically by trapping them in a porous mesh which allows air to pass through but holds back solids. v Sulfur Removal - Switch from soft coal with a high sulfur content to low sulfur coal. - Change to another fuel (natural gas). 36
Air Pollution Control • • Nitrogen Oxides v Best method is to prevent creation. - Staged Burners - Selective Catalysts Hydrocarbon Control v Use closed systems to prevent escape of fugitive emissions. 37
CLEAN AIR LEGISLATION • • Clean Air Act (1963) - First national air pollution control. Clean Air Act (1970) rewrote original. v Identified critical pollutants. v Established ambient air quality standards. - Primary Standards - Human health - Secondary Standards - Materials, environment, aesthetic and comfort. 38
CURRENT CONDITIONS AND FUTURE PROSPECTS • • In the United States, air quality has improved dramatically in the last decade in terms of major large-volume pollutants. v Cities where pollution is largely from traffic still have serious air quality problems. Major metropolitan areas of many developing countries are growing at explosive rates, and environmental quality is very poor. 39
Air Pollution in Developing Countries • Many metropolitan areas of developing countries are growing at explosive rates. v Mexico City - Pollution levels exceed WHO health standards 350 days per year. v China’s 400, 000 factories have no air pollution controls. 40
Signs of Hope • • • Sweden and West Germany cut their sulfur emission by two-thirds between 1970 and 1985. Australia and Switzerland even regulate motorcycle emissions. South Coast Air Quality Management District in California has adopted rules to clean the air in the Los Angeles Basin. 41
Summary • • Natural Sources Human-Caused Air Pollution v Conventional Pollutants v Unconventional Pollutants v Indoor Air Pollution Climate and Topography Effects of Air Pollution Control Clean Air Legislation Current Conditions and Future Prospects 42
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