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PHOTOCHEMICAL AEROSOL DYNAMICS
Citation:
Friedlander, S. PHOTOCHEMICAL AEROSOL DYNAMICS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/3-79/052.
Description:
New data are reported on (1) the rate of formation of condensable chemical species by photochemical reactions, (2) the effect of the reaction products on the particle size distribution and (3) the distribution of reaction products as a function of particle size. Gas-to-particle conversion for cyclopentene, cyclohexene and 1,7--octadiene, ranged from 5 to 39 percent of the initial gas-phase carbon concentrations. Size distribution data for cyclohexene were correlated by a diffusion controlled growth law with Kelvin cutoff diameter at about 0.25 micrometer. In polluted atmospheres, some new particle formation takes place as a result of homogeneous gas phase reactions even though an aerosol is already present. To explain the results of laboratory studies of this phenomenon, classical nucleation theory must be modified to take into account the scavenging of clusters by the aerosol. Using a new low pressure impactor, the first measurements have been made of the distributions of sulfate and nitrate with respect to particle size for dp < 0.25 micrometer. In Pasadena, the data for sulfate often show a peak in the mass distribution for 0.6 < dp < 1.0 micrometer; less often, a peak is observed near 0.1 micrometer, consistent with laboratory data for aerosols formed by homogeneous gas phase reactions.