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FORMATION OF PHOTOCHEMICAL AEROSOLS
Citation:
Stephens, E. AND M. Price. FORMATION OF PHOTOCHEMICAL AEROSOLS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/3-77/044.
Description:
The objective was to develop a better understanding of smog aerosol formation with particular reference to haze in the Southern California area. This study combined laboratory work with ambient air studies. Counting of particles by light scattering was the principle physical technique while infrared analyses was the major source of chemical information. A new reflectance spectroscopy technique was also developed. Infrared spectra of ambient aerosols have bands assigned to sulfate, nitrate, ammonium, and water which are completely removed by water washing of the sample but not by benzene. Synthetic aerosols generated by mixing ammonia with sulfuric and nitric acids produce similar spectra. Many ambient aerosol particles are hygroscopic or deliquescent so that they swell as the relative humidity increases and shrink as it decreases. This readily explains the heavy haze seen at high humidity days. A variety of reaction products (SO4(-2), NO3(-), organics) can potentially fulfill the requirement of water solubility and hygroscopicity to contribute to haze and loss of visibility. It is concluded that direct control of aerosol emissions will not markedly improve visibility in Southern California.