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Aerometric Factors Affecting the Evolution of the Pasadena Aerosol

Hidy, G. M. and Mueller, P. K. and Tokiwa, Y. and Twiss, S. (1972) Aerometric Factors Affecting the Evolution of the Pasadena Aerosol. In: Aerosols and Atmospheric Chemistry. Academic Press , New York, NY, pp. 219-236. ISBN 978-0-12-347250-2.

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This paper describes briefly the meteorological background and the aerometric measurements conducted during the 1969 Pasadena smog experiment. Observations of the winds, the air temperature, humidity, and incoming solar radiation at the experiment site, with support of U. S. Weather Bureau data, indicated that the weather during the study was generally quite regular and was consistent with the Southern California climatology. The winds were light and mainly from the southwest sector during the day, indicating that the polluted air observed in Pasadena would be a complicated mixture of material produced locally and entering the area from distant sources. The observations of such gases as CO, NO, NO_2, oxidant (mostly ozone), hydrocarbons, and SO_2 bore out this conjecture in that the hourly concentration patterns were somewhat variable from day to day. The diurnal averages of such data were more revealing in trends, however, showing typical changes of gases linked with the smog reactions observed during other similar studies. Of particular interest was the simultaneous peaking of SO_2 with ozone at midday. Accompanying the midday maximum of ozone was a maximum in the scattering coefficient b_(scat) as observed by an integrating nephelometer. The frequently observed visibility restrictions during periods of photochemical smog formation have been associated with changes occurring principally in the 0.1- to 1.0-μm diameter range of particles. Comparison between the diurnal average variations of the total number concentration of aerosols N the average surface area S and the volume fraction φ showed different behavior. While N increased throughout the daylight hours until late afternoon, φ displayed a peak at midday in a manner similar to the behavior of ozone. S showed a broad maximum through the daylight hours. Since S and φ are linked mainly with the fraction of suspended particles greater than 0.1-μm diameter, this portion of the particle size spectrum may have evolved by photochemically induced interaction with the suspending gases. Two possible mechanisms for the growth of the large particle fraction are inferred. The first involves heterogeneous nucleation of condensable vapors, and the second postulates a combination of particle coagulation and photochemical reactions of low molecular-weight hydrocarbons, nitrogen compounds, and sulfur dioxide on the surface of small particles.

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Additional Information:© 1972 Academic Press. Received September 28, 1971; accepted September 28, 1971. We are grateful to K. Smith and Mrs. Janya Husar for the contributions to the sampling program and data processing. T. Belsky and F. Yoon conducted the gas chromatographic determination of hydrocarbons. We thank Professor K. T. Whitby and colleagues for use of their aerosol observations and the Los Angeles County Air Pollution Control District for use of their data on CO and hydrocarbons. This project was supported, in part, by the U. S. Public Health Service under Grant AP-00580.
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US Public Health Service (USPHS)AP-00580
Record Number:CaltechAUTHORS:20150805-120014665
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Official Citation:G.M. HIDY, P.K. MUELLER, Y. TOKIWA and S. TWISS, Aerometric Factors Affecting the Evolution of the Pasadena Aerosol, In Aerosols and Atmospheric Chemistry, edited by G.M. HIDY, Academic Press, 1972, Pages 219-236, ISBN 9780123472502, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59244
Deposited By: George Porter
Deposited On:06 Aug 2015 21:16
Last Modified:10 Nov 2021 22:17

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