Model for rain composition and the washout of sulfur dioxide

Technical Report · Thu Jul 01 04:00:00 EDT 1976

DOI:https://doi.org/10.2172/7330342· OSTI ID:7330342

Hill, F B; Adamowicz, R F

A continuous model for the washout of sulfur dioxide from the atmosphere by rain was developed in which account was taken of mass transfer of SO/sub 2/ into well-mixed drops, ionic equilibrium of sulfur compounds in solution, oxidation of dissolved species to sulfate ion, and presence in the rain of background strong acid or base. Expressions were developed to predict the composition of raindrops as a function of fall distance, the time scale of atmospheric SO/sub 2/ removal, and ground level composition transients during a rain event. Illustrative calculations were made for single drop sizes and for the full spectrum of a model drop-size distribution, with the following results. In the absence of bisulfite oxidation and with an acidic background pH (pH/sub 0/ = 4) the composition of rain was in equilibrium with SO/sub 2/ in the atmosphere after falling 100 to 200m through a mixed layer of pollutant. In contrast, the equilibrium composition was not reached within a fall distance of 2000m for a basic background pH (pH/sub 0/ = 10). Furthermore, a unimodal distribution of pH with drop size was found in initially neutral or acidic rain whereas a bimodal distribution appeared with a strongly basic background pH. Introduction of bisulfite oxidation led to enhanced SO/sub 2/ uptake at pH/sub 0/ = 4, and diminished uptake at pH/sub 0/ = 10. Also, rejection of SO/sub 2/ from raindrops of small size was found in the presence of oxidation at pH/sub 0/ = 10. Half-lives for SO/sub 2/ removal from the atmosphere at a 1 mm/hr rainfall rate and a mixed layer height of 1 Km ranged from hours to days depending on background pH and initial SO/sub 2/ atmospheric concentration.

• Research Organization: Brookhaven National Lab., Upton, N.Y. (USA)
• Sponsoring Organization: US Energy Research and Development Administration (ERDA)
• DOE Contract Number: E(30-1)-16
• OSTI ID: 7330342
• Report Number(s): BNL-21794
• Country of Publication: United States
• Language: English

Related Subjects

500200* -- Environment
Atmospheric-- Chemicals Monitoring & Transport-- (-1989)
54 ENVIRONMENTAL SCIENCES
AIR POLLUTION
ATMOSPHERIC PRECIPITATIONS
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
IONS
MATHEMATICAL MODELS
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PH VALUE
POLLUTION
PRECIPITATION SCAVENGING
RAIN
SEPARATION PROCESSES
SULFATES
SULFUR COMPOUNDS
SULFUR DIOXIDE
SULFUR OXIDES
WASHOUT