chapter_17 - Air Pollution Air This chapter discusses: 1....

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Unformatted text preview: Air Pollution Air This chapter discusses: 1. Air pollution types, sources, and trends, including Air tropospheric and stratospheric ozone tropospheric 1. Meteorologic and topographic effects on air Meteorologic pollution, as well as pollution in the urban environment environment Types & Sources of Air Pollution Types Primary air Primary pollutants enter the atmosphere directly, while secondary pollutants form by chemical reaction. reaction. Pollutant Pollutant sources are both natural, such as volcanoes and forest fires, and human caused, such as cars and industry. industry. Figure 17.1 Principal Air Pollutants Principal Carbon monoxide, Carbon sulfur oxides, nitrogen oxides, volatile organic compounds, and particulate matter are the most prevalent primary pollutants, and transportation and power generation are the primary sources for these pollutants. pollutants. Figure 17.2A Figure 17.2B Particulate Matter Pollution Particulate Figure 17.3B Figure 17.3B Particulates are classified as having diameters greater than 10 um Particulates and less than 2.5 um. and PM-10 pollutants settle out of the atmosphere relatively quickly PM-10 compared with the lingering PM-2.5. Both can adversely affect human health and reduce visibility. Both Visible & Invisible Pollutants Visible Figure 17.4 Suspended hygroscopic particles may scatter light and create a Suspended white wet-haze, while carbon monoxide and sulfur dioxide are not visible. visible. The reaction of nitrogen dioxide and hydrocarbons may generate The unsightly photochemical smog. unsightly Ozone in the Troposphere Ozone Figure 17.5 Human health is compromised by exposure to ozone and Human photochemical smog, which is formed when on a daily cycle when sunlight dissociates NO2. The product O reacts with atmospheric O2 to create O3. Usually, the product NO would then react with and destroy the 03. Usually, Excessive hydrocarbons, often from automobile exhaust, react with Excessive the product NO and O3 concentrations increase to harmful levels. the Ozone in the Stratosphere Ozone UV radiation has enough UV energy to adversely impact the health of plants and animals, including humans. animals, Naturally occurring O3 in the Naturally stratosphere can block the most harmful UV radiation from entering the troposphere. troposphere. Figure 17.6 Stratospheric Ozone Destruction Stratospheric Naturally destructive Naturally agents of ozone include NO and NO2, or oxides of nitrogen, which largely originate from bacterial activity at the earth's surface. surface. Human released Human chlorofluorocarbons (CFCs) have upset the balance of O3 production and destruction, and have caused formation of ozone holes and an increase in human UV exposure. exposure. Figure 17.7 Air Pollution Patterns & Trends Air Figure 17.8 Air quality in the U.S. may have been at its worst in the 1970s, but programs implemented by the Clean Air Act have helped the U.S. move toward primary ambient air quality standards. ambient Regional Air Quality Indices may identify certain Regional non-attainment areas, which are then targeted by the Environmental Protection Agency for improvement. Environmental Trends in Tropospheric Ozone Trends Yearly ozone trends are Yearly influenced by hot sunny weather and light surface winds, but many cities have demonstrated an overall decline in harmful ozone levels during the 1980s. levels Figure 17.9 Wind & Air Pollution Wind Figure 17.10A Figure 17.10B Wind may move along and dilute pollutants through advection and Wind turbulent mixing, but when winds slow, the pollutants become more concentrated. concentrated. Pollutants & Radiation Inversions Pollutants Figure 17.11 Radiation temperature inversions, often lasting only a few hours at Radiation morning with warm air above cold, creates a stable atmosphere and traps pollutants at the surface. traps Pollutant sources above the inversion will lift beyond the city, but Pollutant likely settle down as a pollutant downstream. likely Pollution & Subsidence Inversions Pollution Subsidence Subsidence inversions may last for several days, which can create major pollution threats by reducing the mixing depth and layer, forcing a build-up of unwanted pollutants in the urban environment. environment. Figure 17.12 California's Pacific High California's The semi The permanent Pacific high promotes subsiding, and warming, air to settle over the southern coastal cities and trap pollutants much of June to October. June Figure 17.13 Pollutants & Topography Pollutants Air movement Air from higher hills to valleys can strengthen prestrengthen existing surface existing inversions, as well as carry pollutants downhill, particularly in the colder months. colder Los Angeles and Los Denver are two major cities where air pollution is exacerbated by topography. topography. Figure 17.15 Pollution in the Urban Environment Pollution Figure 17.16 Human activity and the reduced amount of water and vegetation in Human cities creates an urban heat island, or area of greater temperature than surrounding country side. than The temperature differential can set up a country breeze, and bring The pollen and rural dust into the city. pollen Acid Rain & Fog Acid Atmospheric Atmospheric concentrations of CO2 make rainfall slightly acidic between 5.0 and 5.6 pH, but power plant emissions of sulfur and nitrogen oxides form additional acids that may drop rainfall acidity from 4.0 to 4.5 in the northeastern U.S. Figure 17.17 Impacts of Acid Rain & Fog Impacts Figure 17.18 Atmospheric transport of Atmospheric acidic gasses and condensation nuclei ends when rain droplets precipitate due to orographic features or fog is scrubbed by mountaintop trees. mountaintop Figure 17.19 ...
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