Chapter 13 Notes Air Pollution

Sever Air-Pollution Episode in China Air quality is not just a function of the quantity and types of pollutants emitted into the air; it is also closely linked to the atmosphere’s ability to disperse these noxious substances. Dispersal, in turn, is related to the stability of the atmosphere.

Wildfires Caused by Lightning-Strikes in California Air is never perfectly clean. Many natural sources of air pollution have always existed. Natural air pollution sources include ash from volcanic eruptions, salt particles from breaking waves, pollen and spores release by plants, smoke from forest and brushfires, and windblown dust.

Air pollutants are airborne particles and gases that occur concentrations that endanger the health and well-being of organisms or disrupt the orderly function of the environment. Primary pollutants are emitted directly from identifiable sources; they pollute the air immediately upon being emitted. Secondary pollutants are produced in the atmosphere when certain chemical reactions take place among primary pollutants. In some cases the impact of primary pollutants on human health and the environment are less severe than the effects of the secondary pollutants they form.

Emission Estimates for Primary Pollutants in the U.S. in 2007 The major sources for each primary varies, fro example electricity generation is the primary source for sulfur dioxide, while on-road vehicles is the primary source for carbon monoxide, nitrogen oxides, volatile organic compounds.

Particulate Matter Particulate Matter – the general term used for a mixture of solid particles and liquid droplets found in the air. Some particles are large enough to be seen while other are so small they can be detected only with an electron microscope. Sources include combustion from vehicles, power generation, industrial facilities, residential fireplaces and wood stoves, and dust from unpaved roads, materials handling, and crushing and grinding opertaions.

Trends in National Emissions 1900-2007 Sulfur Dioxide – a colorless and corrosive gas that originates largely from the combustion of sulfur=containing fuels, primarily coal and oil. Sources include power plants, smelters, petroleum refineries, and pulp and paper mills. Once in the air, SO2 converts to SO3, combines with water to form sulfuric acid (H2SO4) Nitrogen Oxides – gases that form during the high-temperature combustion of fuel when nitrogen in the fuel or air reacts with oxygen. Motor vehicles and power plants are the primary sources. Nitrogen dioxide can react with atmospheric water to form nitric acid (HNO3) Volatile Organic Compounds – encompass a wide array of solid, liquid, and gaseous substances that are composed exclusively of hydrogen and carbon. In cities, the incomplete combustion of gasoline in motor vehicles is the principal source of reactive VOCs. Alone, VOCs do not appear to pose significant environmental problems, but they can react with certain other pollutants to form noxious secondary pollutants.

People Living in Areas with Air-Quality Concentrations of Pollutants above National Standard Carbon Monoxide – a colorless, odorless , and poisonous gas produced by incomplete burning of carbon in fuels. The most abundant primary pollutant, with more than three-quarters of the national emissions coming from highway vehicles and non-road equipment. Lead – is dangerous because it accumulates in the blood, bones, and soft tissues. It can impair the functioning of many organs. In the past, automotive sources were the major contributor of lead emission to the atmosphere because lead was added to gasoline to prevent engine knock. With the phase-out of leaded gas, the concentrations of lead in the air have shown a dramatic decline.

London’s Infamous 1952 “Great Smog” Secondary pollutants Secondary pollutants form in the atmosphere when reactions take place among primary pollutants. Air pollution in urban and industrial areas is often termed smog, a word that is formed by the combining of “smoke” and “fog”. Today the word is used as a synonym for general air pollution. Many reactions that produce secondary pollutants are triggered by strong sunlight and are called photochemical reactions.

Comparison of Growth Areas and Emissions 1970-2007 Trends in Air Quality Economic activity, population growth, meteorological conditions, and regulatory efforts to control emissions all influence the trends in air pollutant emissions. Up until the 1950s the greatest influences on emissions were related to the economy and population growth. Emissions grew as the economy and population increased. In the 1950s the states issued air-pollution statutes generally targeted toward smoke and particulate emissions. The passage of the federal Clean Air Act in 1970 started efforts to reduce air pollution in a major way. The Clean Air Act of 1970 mandated the setting of standards for four of the primary pollutants—particulates, sulfur dioxide, carbon monoxide, and nitrogen oxides—as well as the secondary pollutant ozone. The Clean Air Act has been amended on more than one occasion, with new standards set for the majors pollutants.

National Air-Quality Forecast Map; August 2008 Meteorological Factors Affecting Air Pollution Two of the most important factors affecting the dispersion of pollutants are (1) the strength of the wind, and (2)the stability of the air. These factors are critical because they determine how rapidly pollutants are diluted by mixing with the surrounding oar after leaving the source. Wind speed influences the concentration of pollutants. The faster the wind the lower the concentration of pollutants, and faster winds create greater turbulence which result in a more rapid mixing of pollutants and ‘clean” air. Atmospheric stability determines the extent to which vertical motions will mix the pollution with cleaner air above. The vertical distance between Earth’s surface and the height to which convectional movements extend is called the mixing depth. Generally, the greater the mixing depth, the better the air quality because the pollutants are mixed through a larger volume of cleaner air.