Air Quality and Pollution

1. Air Quality and Pollution The challenge to manage our atmospheric resources well

2. Outline • Atmospheric stability and pollution dispersion • Vertical stability • Adiabatic lapse rate • Thermal Inversions • Survey of “criteria” pollutants • Emissions and concentrations • Atmospheric reactions • Effects

3. 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. T2 = Tair2 T1 > Tair1

4. 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.

5. Adiabatic Lapse Rate h stable • 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 ALR unstable hs 270K 290K 320K T

6. Thermal Inversions h Subsidence Inversion • 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. Radiative Inversion T

7. Atmospheric Temperature

8. 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.

9. Pollution Concentrations • Pollution levels are measured in either PPM (parts per million) or in g/m3. • 1 mole of anything contains NA = 6.02 x 1023 particles. • 1 mole of gas at STP occupies 0.0224 m3 . • The “particle density” is then 2.69 x 1025 particles per m3. • 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 m3, 2.69 x 1019 molecules of pollutant are present. • To convert to g/m3, we just need to know the mass per mole

10. 6 Criteria Pollutants • The federal EPA has identified 6 critical pollutants which are monitored nationwide. • CO, SOx, O3 (VOC’s), NOx, 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

11. The EPA website • http://www.epa.gov/oar/aqtrnd97/brochure/sixprin.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.

12. Other areas of concern • Acid Rain • Visibility • Global warming • Stratospheric Ozone depletion • Radioactive wastes