Gas and aerosol scavenging
The wet removal rate and wet deposition of pollutants is ultimately dependent upon the rate of pollutant attachment to the falling precipitation particles (hydrometeors) and to the precipitation flux at the ground. This attachment to the hydrometeors or collector particles is, in turn, dependent upon the physical characteristics of the pollutant. As expected, when considering wet removal, gases behave differently from aerosols. Modelers of gas scavenging (e.g., Hales 1972, Adamowitz 1979) stress the importance of drop size distribution, vertical gradients of gas concentration in the atmosphere and solubility in determining gas deposition at the surface. Aerosols, on the other hand, are removed at various rates depending upon aerosol size distribution, solubility, environmental humidity and age. Before the specifics of wet removal are dealt with, it is helpful to present some of the basic mathematical concepts used for treating problems in precipitation scavenging. By doing so, current terminology can be introduced and placed into a framework that should alleviate confusion about meaning. For example, a distinction between scavenging coefficients and simply scavenging will be made. The terminology in-cloud, below-cloud, washout, and rainout are shown to be ambiguous and will be dismissed. Other concepts, such as washout ratio, nucleation scavenging, vapor deposition versus accretion are shown to be more appropriate or useful when considering wet removal of aerosol and gas. Gas and aerosol removal are considered in general. For each, the emphasis is upon surface deposition, and upon properties that must be known to approximate wet surface fluxes. In the final section, the suspected properties of organics and metals are presented and related to wet removal.
- Research Organization:
- Battelle Pacific Northwest Labs., Richland, WA (USA)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 5180474
- Report Number(s):
- PNL-SA-8170; CONF-7911105-1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Atmospheric-- Chemicals Monitoring & Transport-- (-1989)
54 ENVIRONMENTAL SCIENCES
AEROSOLS
AIR POLLUTION
ATMOSPHERIC CHEMISTRY
ATMOSPHERIC PRECIPITATIONS
CHEMICAL REACTION KINETICS
CHEMISTRY
CLOUDS
COLLOIDS
DATA
DATA COMPILATION
DATA FORMS
DISPERSIONS
DISTRIBUTION
ELEMENTS
FLUIDS
GASES
INFORMATION
KINETICS
METALS
NUCLEATION
NUMERICAL DATA
ORGANIC COMPOUNDS
PARTICLE SIZE
POLLUTION
PRECIPITATION SCAVENGING
QUANTITY RATIO
REACTION KINETICS
REMOVAL
SCAVENGING
SEPARATION PROCESSES
SIZE
SNOW
SOLS
TABLES
WASHOUT