Air Quality and PollutionAir Quality and Pollution

The challenge to manage our atmospheric resources well

OutlineOutline Atmospheric stability and pollution dispersion

Vertical stabilityAdiabatic lapse rateThermal Inversions

Survey of “criteria” pollutantsEmissions and concentrationsAtmospheric reactionsEffects

Seeking Vertical EquilibriumSeeking 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

T1 > Tair1

= Tair2

Atmospheric Stability: Part IIAtmospheric 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.

Adiabatic Lapse RateAdiabatic 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

hs

unstable

stable

320K290K270K

Thermal InversionsThermal 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

SubsidenceInversion

RadiativeInversion

Atmospheric TemperatureAtmospheric Temperature

Atmospheric DispersionAtmospheric 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.

Pollution ConcentrationsPollution 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

6 Criteria Pollutants6 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

The EPA websiteThe 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.

Other areas of concernOther areas of concern

Acid Rain Visibility Global warming Stratospheric Ozone depletion Radioactive wastes