ENSP101Chapter 16 – Air Pollution16.1 The Air Around Us- Smoke, haze, dust, odors, corrosive gases, noise, and toxic compounds are present nearly everywhere, even in the most remote, pristine wilderness- Air pollution is generally the most widespread and obvious kind of environmental damage- Total worldwide emissions of these pollutants are around 2 billion metric tons per year- Over the past 30 years, however, air quality has improved appreciably in most cities in Europe, North America, and Japan16.2 Natural Sources of Air Pollution- Many natural sources of air quality degradation:o Volcanoes spew out ash, acid mists, hydrogen sulfide, and other toxic gaseso Sea spray and decaying vegetation are major sources of reactive sulfur compounds in the airo Trees and bushes emit millions of tons of volatile organic compounds (terpnes and isoprenes)o Pollen, spores, viruses, bacteria, and other small bits of organic material in the air cause widespread suffering from allergies and airborne infectionso Storms in arid regions raise dust clouds that transport millions of tons of soil and can be detected half a world awayo Bacterial metabolism of decaying vegetation in swamps and of cellulose in the guts of termites and ruminant animals is responsible for as much as 2/3 of the methane in the air16.3 Human-caused Air Pollution- Primary pollutants – chemicals released directly into the air in a harmful form- Secondary pollutants – chemicals modified to a hazardous form after entering the air or thatare formed by chemical reactions as components of the air mix and interacto Solar radiation often provides the energy for these reactions- Fugitive emissions – substances that enter the air without going through a smokestacko Dust from soil erosion, strip mining, rock crushing, and building construction- The US Clean Air Act of 1970 designated 7 major pollutants (sulfur dioxide, carbon monoxide, particulates, hydrocarbons, nitrogen oxides, photochemical oxidants, and lead) for which maximum ambient air (air around us) levels are mandatedo These 7 conventional or criteria pollutants contribute the largest volume of air-quality degradation and also are considered the most serious threat to human health and welfareEstimated Fluxes of Pollutants and Trace Gases to the AtmosphereSpecies Sources Natural AnthropogenicCO2 (carbon dioxide)Respiration, fossil fuelburning, land clearing,industrial processes37,000 29,600Rice paddies and wetlands,CH4 (methane) gas drilling, landfills,animals, termites155 350CO (carbon monoxide)Incomplete combustion,CH4 oxidation, biomassburning, plant metabolism1,580 930NMHC (nonmethanehydrocarbons)Fossil fuels, industrial uses,plant isprenes and otherbiogenics860 92NOx (nitrogen oxides) Fossil fuel burning,lightning, biomass burning,soil microbes90 140SOx (sulfur oxides) Fossil fuel burning,industry, biomass burning,volcanoes, oceans35 79SPM (suspended particulatematerials)Biomass burning, dust, seasalt, biogenic aerosols, gas-to-particulate conversion583 362o Sulfur compounds: Natural sources of sulfur in the atmosphere include evaporation of sea spray, erosion of sulfate-containing dust from arid soils, fumes from volcanoes and fumaroles, and biogenic emissions of hydrogen sulfide and organic sulfur-containing compounds Total yearly emissions of sulfur  114 million metric tons Anthropogenic sources  90% of sulfur in the air Sulfur dioxide –- Once in the atmosphere, it can be further oxidized to sulfur trioxide (SO3) which reacts with water vapor or dissolves in water droplets to form sulfuric acid, a major component of acid raino Nitrogen compounds: Nitrogen oxides – highly reactive gases formed when nitrogen in fuel or combustion air is heated to over 650C in the presence of oxygen or when bacteria in soil or water oxidize nitrogen-containing compounds The initial product, nitric oxide (NO), oxidizes further in the atmosphere to nitrogen dioxide (NO2), a reddish brown gas that gives photochemical smog its distinctive color Total annual emissions of reactive nitrogen compounds  230 million metric tons worldwide Anthropogenic sources  60% of nitrogen in the air Nitrous oxide (N2O) is an intermediate in soil denitrification that absorbs UVlight and plays an important role in climate modificationo Carbon oxides: Predominant form of carbon in the air is carbon dioxide (CO2) Nontoxic and innocuous Increasing atmospheric levels (about 0.5% per year) causing global climate change that may have disastrous effects on both human and natural communities Anthropogenic CO2 releases are difficult to quantify because they spread across global scales- The best current estimate is that between 7 and 8 billion tons of carbon (in the form of CO2) are released each year by fossil fuel combustion and that another 1 to 2 billion tons are released byforest and grass fires, cement manufacturing, and other human activities- Terrestrial ecosystems take up about 3 billion tons of this excess carbon every year, while oceanic processes take up another 2 billion tons- This leaves an average of at least 3 billion tons to accumulate in the atmosphere Carbon monoxide – colorless, odorless, nonirritating but highly toxic gas produced by incomplete combustion of fuel, incineration of biomass or solid waste, or partially anaerobic decomposition of organic material- About 1 billion metric tons of Co are released to the atmosphere eachyear, half of them from human activities- About 90% of the Co in the air is consumed in photochemical reactions that produce ozoneo Particulate material: Aerosols – minute particles or liquid droplets suspended in the air Particulate material – atmospheric aerosols; originally applied only to solid particles but now extended to droplets of liquid- This includes dust, ash, soot, lint, smoke, pollen, spores, algal cells, and man other suspended materials Anthropogenic particulate emissions amount to about 362 million metric tons per year worldwide Particulates often are the most apparent form of air pollution- Asbestos fibers and cigarette smoke are among the most dangerous respirable particles in urban and indoor air because they are carcinogenic- Diesel fumes also are highly toxic Soil conservation techniques have reduced dust storms in N. America, but deserts and dust storms have increased elsewhere 3 billion tons of sand and soil blow from dry lands around the world every year- Raises