ENSP101 Chapter 16 Air Pollution 16 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 Japan 16 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 gases o Sea spray and decaying vegetation are major sources of reactive sulfur compounds in the air isoprenes o Trees and bushes emit millions of tons of volatile organic compounds terpnes and o Pollen spores viruses bacteria and other small bits of organic material in the air cause widespread suffering from allergies and airborne infections o Storms in arid regions raise dust clouds that transport millions of tons of soil and can be detected half a world away o 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 air 16 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 that are formed by chemical reactions as components of the air mix and interact o Solar radiation often provides the energy for these reactions Fugitive emissions substances that enter the air without going through a smokestack o 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 mandated o 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 welfare Species CO2 carbon dioxide Sources Respiration fossil fuel burning land clearing industrial processes Rice paddies and wetlands Estimated Fluxes of Pollutants and Trace Gases to the Atmosphere Natural 37 000 Anthropogenic 29 600 CH4 methane CO carbon monoxide NMHC nonmethane hydrocarbons NOx nitrogen oxides SOx sulfur oxides SPM suspended particulate materials gas drilling landfills animals termites Incomplete combustion CH4 oxidation biomass burning plant metabolism Fossil fuels industrial uses plant isprenes and other biogenics Fossil fuel burning lightning biomass burning soil microbes Fossil fuel burning industry biomass burning volcanoes oceans Biomass burning dust sea salt biogenic aerosols gas to particulate conversion o Sulfur compounds 155 1 580 860 90 35 583 350 930 92 140 79 362 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 rain o 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 UV light and plays an important role in climate modification o Carbon oxides Nontoxic and innocuous Predominant form of carbon in the air is carbon dioxide CO2 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 by forest 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 each year half of them from human activities About 90 of the Co in the air is consumed in photochemical o Particulate material reactions that produce ozone 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 particulate levels above federal health standards Benefit Rainforest depends on mineral nutrients carried in dust from Africa Airborne dust is considered the primary source of allergies worldwide Many