Study of the mechanisms of acid rain formation
Samples of rain, snow, cloud water, aerosols and soil were collected in Colorado to study the mechanisms of acid rain formation. Chemical compositions of various types of samples were analyzed to investigate the stepwise incorporation of inpurities into precipitation. Local soil was generally alkaline; atmospheric aerosols, which are mixtures of stirred-up soil particles and anthropogenic pollution, were slightly acidic; cloud condensation nuclei, which initiate clouds at condensation level, had an average pH of approx.6. However, local clouds were very acidic (pH approx.4), indicating that further acidification takes place in clouds by adsorption of acidic gases, e.g., CO/sub 2/, SO/sub 2/, and NO/sub x/. We found that summer showers formed by coalescence of cloud droplets are likely to be as acidic as cloud water. The chemistry of snow may differ from that of clouds, depending on the mechanisms of snow formation. If snow crystals are initiated by deposition nucleation and grown by diffusion of water vapor from surrounding evaporating cloud droplets as in the Bergeron--Findeisen process, the snow crystals are purified and should not be acidic. If the snow crystals are initiated by freezing of cloud droplets and grow by vapor diffusion, then the constituents of cloud water are diluted and the snow is less acidic than cloud water. If snow grains (graupel) are formed by accretion of frozen cloud drops or by riming, the snow can be as acidic as cloud water. Raindrops formed by melting snow inherit the chemistry of the parent snow, but differentiate in scavenging coefficiencies of gases and aerosols below the clouds. Both atmospheric chemical reactions and cloud microphysical processes are responsible for chemical variations in precipitation.
- Research Organization:
- National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Environmental Sciences Group, Boulder, CO 80303
- OSTI ID:
- 5655254
- Journal Information:
- J. Atmos. Sci.; (United States), Vol. 44:21
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ACID RAIN
SYNTHESIS
AEROSOLS
ATMOSPHERIC CHEMISTRY
CHEMICAL COMPOSITION
CLOUDS
COLORADO
PH VALUE
PRECURSOR
RAIN
SNOW
SOILS
ATMOSPHERIC PRECIPITATIONS
CHEMISTRY
COLLOIDS
DISPERSIONS
FEDERAL REGION VIII
NORTH AMERICA
SOLS
USA
500200* - Environment
Atmospheric- Chemicals Monitoring & Transport- (-1989)