Accession Number : ADA185002

Title :   Preliminary Investigation of the Role that DMS (Dimethyl Sulfide) and Cloud Cycles Play in the Formation of the Aerosol Size Distribution.

Descriptive Note : Interim rept.,

Corporate Author : NAVAL RESEARCH LAB WASHINGTON DC

Personal Author(s) : Hoppel, W A ; Fitzgerald, J W ; Frick, G M ; Larson, R E ; Wattle, B J

PDF Url : ADA185002

Report Date : 29 Jul 1987

Pagination or Media Count : 37

Abstract : A series of experiments designed to study the production of new particulate matter by photolysis of dimethyl sulfide (DMS) and the effect that nonprecipitating clouds, have on the aerosol size distributions were carried out in Calspan Corporation's 600 cum environmental chamber during January and February 1986. The results show that DMS, the most abundant natural source of sulfur, is photooxidized to some product of low volatility that can form new particles by homogeneous nucleation or condense on existing aerosols causing them to grow. To explain these observations, a theoretical study of the nucleation properties of methane sulfonic acid (MSA) was undertaken. The nucleation thresholds, calculated using thermodynamic data for MSA, show that at 70% RH, and MSA concentration of only 0.006 ppb will result in a supersaturated environment in which MSA will condense on preexisting particles larger than 0.02 micron radius. If the MSA concentrations increase to 30 ppb, then spontaneous formation of MSA solution droplets occurs by homogeneous binary nucleation. Simulations of the evolution of the size distribution observed for the DMS irradiation experiments with a dynamic aerosol model that includes the effects of coagulation, growth by condensation, and deposition to the walls of the chamber, yield results that are in excellent agreement with the observed evolution.

Descriptors :   *PARTICULATES, *AEROSOLS, *PARTICLE SIZE, *SULFIDES, *CLOUDS, METHANE, SULFONIC ACIDS, GROWTH(GENERAL), VAPOR DEPOSITION, PHOTOLYSIS, NUCLEATION, INTERSTITIAL, DROPS, COAGULATION, ATMOSPHERIC CONDENSATION, THERMODYNAMICS

Subject Categories : Atmospheric Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE