Part 5. Human Activities Chapter 14 Human Effects: Air Pollution and Heat Islands.
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Part 5. Human Activities Chapter 14 Human Effects: Air Pollution and Heat Islands
Introduction Air pollutants are gases, liquids or solids in the air that can adversely affect plant and/or animal life Primary pollutants are pollutants that are emitted directly by natural or anthropogenic (manmade) processes Secondary pollutants are pollutants that arise from chemical reactions of atmospheric gases with gases emitted by natural or anthropogenic processes
Important Air Pollutants Particulates (aerosols) are solid or liquid particles suspended in the air (from.1 to 100 m in size) Natural sources -- fires, volcanic eruptions, salt spray from the oceans, pollen, dust storms Anthropogenic sources -- combustion of fossil fuels PM 10 (< 10 m) enters lungs (associated with asthma); PM 2.5 even more dangerous (lung cancer) Particulates stay in the atmosphere no more than a few years
Carbon oxides - CO x CO -- Carbon monoxide –Colorless, odorless gas from volcanic eruptions, forest fires, bacterial activities, fuel combustion –Dangerous to humans and animals in high concentrations CO 2 -- Carbon dioxide –Colorless, odorless gas from volcanic eruptions, forest fires, bacterial activities, fuel combustion –Is an important greenhouse gas; in high concentrations can displace oxygen ( CO 2 is denser than O 2 )
Sulphur oxides - SO x Have both gaseous and aerosol forms Natural sources are bacterial release, volcanic eruptions, sea spray Anthropogenic sources are combustion of fossil fuels and ore smelting –SO 2 is a respiratory irritant –SO 3 contributes to acid fog and acid rain
Acid precipitation across North America Factories and power plants in the midwest and northeast contribute sulphur oxides to the air. These pollutants cause acid rain downwind of their sources of emission.
Acid deposition weathers monuments and buildings Acid rain dissolves limestone components of buildings.
Nitrogen oxides - NO x Nitric oxide (NO) and Nitrogen dioxide (NO 2 ) Natural sources are biological processes in soil and water Anthropogenic sources are fossil fuel combustion NO 2 is a toxic yellow to reddish-brown gas (like Los Angeles smog) that is pungent and corrosive –Can cause pulmonary health problems
Volatile organic compounds or VOCs (hydrocarbons) Methane, butane, propane, octane, gasoline, paint thinners, etc. Natural sources are organic emissions and decomposition of organic matter Anthropogenic sources are primarily combustion from automobiles, trucks, buses, and other fossil fuel motors; also evaporation of gasoline and other chemicals Combines with solar radiation to form Los Angeles- type photochemical smog; ozone is a major secondary pollutant from VOCs –Ozone causes respiratory and heart problems
U.S. Anthropogenic Air Pollution Sources Major Sources: -Fuel combustion (electricity generation and heating) -Transportation -Industrial Processes
Atmospheric Controls on Air Pollution High concentrations of pollutants in a small area (usually due to anthropogenic sources) are the biggest air pollution problems The horizontal and vertical transport of air pollutants by winds help control the local concentrations of pollutants Concentrations are inversely proportional to wind speed Eddies can mix air vertically Inversions can trap pollutants near the Earth’s surface
Effect of wind speed on pollution Lower winds allow greater concentrations of pollutants. Greater winds reduce concentrations of pollutants by spreading them faster and farther.
U.S. pollution trends since 1977: Anthropogenic pollution has been decreasing since the first clean air laws were passed in the 1970s. Lead was prohibited in gasoline in the mid 1970s.
Urban Heat Island effect -- cities have higher average temperatures at night than surrounding area Causes of the urban heat island effect: low albedo, low evaporation, IR radiation trapped by tall buildings, heat absorption by roads and other surfaces, few trees and plants, etc. High particulate concentrations in cities reflect some sunlight and can stimulate downwind cloud/precipitation processes
City center is warmer than the surrounding suburbs and countryside.