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Air Quality and Pollution The challenge to manage our atmospheric resources well
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Outline Atmospheric stability and pollution dispersion Vertical stability Adiabatic lapse rate Thermal Inversions Survey of “criteria” pollutants Emissions and concentrations Atmospheric reactions Effects
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Seeking Vertical Equilibrium As hot air rises, the pressure decreases, the temperature drops and the density drops. When it reaches air of the same temperature (and density), it stops rising. T2T2 T1T1 > Tair 1 = Tair 2
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Atmospheric Stability: Part II A vertically stable atmosphere is one in which denser air is below and less dense air, above. BUT…, if the air below is heated, it will become less dense, and will tend to rise until it reaches air of the same density. Because of the sun’s heating and the earth’s cooling, the air is constantly rising and falling, seeking vertical equilibrium.
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Adiabatic Lapse Rate Air cools as it rises. ALR = -0.65 C / 100m The surrounding air can be cooler or warmer as you go up. If it is warmer, the rising hot air ( e.g. pollution) is trapped. Inversion T h ALR hshs unstable stable 320K290K270K
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Thermal Inversions Radiation Inversion: On clear, winter nights, the earth cools off faster than the air. Lasts the morning hours. Subsidence Inversion: High Pressure region “subsides” onto air below, compressing and heating it. Lasts up to several days. h T Subsidence Inversion Radiative Inversion
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Atmospheric Temperature
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Atmospheric Dispersion Polluted air tends to be hot, initially. As it rises, it tends to cool and disperse. Turbulence due to vertical and horizontal instabilities speed up dispersion, until the pollution is well mixed. “Dilution is the solution to pollution”! Tall stacks designed to increase dispersion.
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Pollution Concentrations Pollution levels are measured in either PPM (parts per million) or in g/m 3. 1 mole of anything contains N A = 6.02 x 10 23 particles. 1 mole of gas at STP occupies 0.0224 m 3. The “particle density” is then 2.69 x 10 25 particles per m 3. A pollutant concentration of 1 ppm tells us that for every 1 MILLION of those particles, ONE of them is the pollutant. It means that in 1 m 3, 2.69 x 10 19 molecules of pollutant are present. To convert to g/m 3, we just need to know the mass per mole
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6 Criteria Pollutants The federal EPA has identified 6 critical pollutants which are monitored nationwide. CO, SO x, O 3 (VOC’s), NO x, Pb, Particulates (PM10). NAAQS = National Ambient Air Quality Standards. These standards set limits on allowable concentrations over time periods from 1 hour to a year. http://www.epa.gov/airs/criteria.html http://www.epa.gov/airs/criteria.html
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The EPA website http://www.epa.gov/oar/aqtrnd97/brochure/sixpri n.html http://www.epa.gov/oar/aqtrnd97/brochure/sixpri n.html The trend is positive, however… 107 million Americans live in counties in violation of one of the standards…that’s about 40%! Illinois, Indiana are in the top three for emissions of particulates, SO and NO.
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Other areas of concern Acid Rain Visibility Global warming Stratospheric Ozone depletion Radioactive wastes
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