Comparison of field data with a thermodynamic model for the H/sub 2/SO/sub 4/ - HNO/sub 3/ - NH/sub 3/ system at high humidities and in fogs
A systematic characterization of the atmospheric H/sub 2/SO/sub 4/ - NH/sub 2/ system was conducted in the fogwater, the aerosol, and the gas phase at a network of sites in the San Joaquin Valley of California. Spatial patterns of concentrations were established that reflect the distribution of SO/sub 2/, NO/sub X/, and NH/sub 3/ emissions within the valley. The concept of atmospheric alkalinity was introduced to interpret these concentrations in terms of the buffering capacity of the atmosphere with respect to inputs of strong acids. Regions of predominantly acidic and alkaline fogwater were identified. Fogwater was found to be alkaline in most of the valley, but small changes in emission budgets could lead to widespread acid fog. An extended stagnation episode was studied in detail: progressive accumulation of H/sub 2/SO/sub 4/ - HNO/sub 3/ - NH/sub 3/ species was documented over the course of the episode, and interpreted in terms of production and removal mechanisms. Secondary production of strong acids H/sub 2/SO/sub 4/ and HNO/sub 3/ under stagnant conditions resulted in a complete titration of available alkalinity at sites furthest from NH/sub 3/ sources. A steady SO/sub 2/ conversion rate of 0.4 - 1.1% h/sup -1/ was estimated in the stagnant mixed layer of haze aerosol under overcast conditions, and was attributed to non-photochemical heterogeneous processes. Removal of SO/sub 2/ was enhanced in fog as compared to non-foggy conditions. Conversion of NO/sub X/ to HNO/sub 3/ slowed down during the stagnation episode because of reduced photochemical activity: fog did not appear to enhance conversion of NO/sub X/. Decreases in total HNO/sub 3/ concentrations were observed upon acidification of the atmosphere, and were attributed to displacement of NO/sub 3-/ by H/sub 2/SO/sub 4/ in the aerosol followed by rapid deposition of HNO/sub 3/(g). The occurrence of fog was associated with general decreases of aerosol concentrations due to enhanced removal by deposition.
- Research Organization:
- Environmental Engineering Science, W.M. Keck Engineering Labs., California Institute of Technology, Pasadena, CA 91125
- OSTI ID:
- 5529747
- Journal Information:
- Am. Chem. Soc., Div. Pet. Chem., Prepr.; (United States), Vol. 31:2
- Country of Publication:
- United States
- Language:
- English
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ACID RAIN
ATMOSPHERIC CHEMISTRY
AMMONIA
AIR POLLUTION MONITORING
ECOLOGICAL CONCENTRATION
CALIFORNIA
AIR QUALITY
NITRIC ACID
SULFURIC ACID
AEROSOLS
FOG
HUMIDITY
MATHEMATICAL MODELS
NITROGEN OXIDES
PH VALUE
SULFUR DIOXIDE
THERMODYNAMICS
ATMOSPHERIC PRECIPITATIONS
CHALCOGENIDES
CHEMISTRY
COLLOIDS
DISPERSIONS
ENVIRONMENTAL QUALITY
FEDERAL REGION IX
HYDRIDES
HYDROGEN COMPOUNDS
INORGANIC ACIDS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NORTH AMERICA
OXIDES
OXYGEN COMPOUNDS
RAIN
SOLS
SULFUR COMPOUNDS
SULFUR OXIDES
USA
500200* - Environment
Atmospheric- Chemicals Monitoring & Transport- (-1989)