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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. D12, 4365, doi:10.1029/2002JD002688, 2003

Evaluating the first-order effect of intraannual temperature variability on urban air pollution

Jeremy Aw

Department of Civil and Environmental Engineering, University of California, Davis, California, USA


Michael J. Kleeman

Department of Civil and Environmental Engineering, University of California, Davis, California, USA


Abstract

The direct effect of intraannual temperature variability on ozone and PM2.5 concentrations at the urban scale was simulated using a high-resolution air quality model that tracks the temperature-dependant formation of secondary organic and inorganic aerosol components. Calculations show that the concentration of ozone and non-volatile secondary particulate matter will generally increase at higher temperatures due to increased gas-phase reaction rates. The concentration of semi-volatile reaction products also will increase at higher temperatures, but the amount of this material that partitions to the particle-phase may decrease as equilibrium vapor pressures rise. Calculations performed for Southern California on September 25, 1996 predict that intraannual temperature variability may cause peak ozone and PM2.5 concentrations to fluctuate by up to 16% and 25% respectively. 24-hour average PM2.5 concentrations will decrease with increasing temperatures for inland portions of the South Coast air basin during most of the day. Slight increases in 24-hour average PM2.5 concentrations were predicted for coastal regions. The majority of the predicted shift in PM2.5 concentrations was related to increased production rates for nitric acid and condensable organic compounds balanced against increased volatilization of these products. Semi-volatile particulate ammonium nitrate concentrations are most sensitive to volatilization losses at hotter temperatures and when the ratio of gas-phase ammonia to nitric acid concentrations is approximately unity. Background sulfate particles and particles released from non-catalyst equipped gasoline-powered engines, diesel engines, and food cooking were shifted to smaller sizes as ammonium nitrate volatilized at hotter temperatures.

Received 21 June 2002; accepted 13 January 2003; published 26 June 2003.

Index Terms: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 1610 Global Change: Atmosphere (0315, 0325).

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Citation: Aw, J., and M. J. Kleeman (2003), Evaluating the first-order effect of intraannual temperature variability on urban air pollution, J. Geophys. Res., 108(D12), 4365, doi:10.1029/2002JD002688.