Secondary organic aerosol formation and transport

Abstract

A Lagrangian trajectory model simulating the formation, transport and deposition of secondary organic aerosol is developed and applied to the Los Angeles area, for the air pollution episode of 27–28 August 1987. The predicted secondary organic aerosol on 28 August 1987 represents 15–22% of the measured particulate organic carbon at inland locations in the base case simulations, and 5–8% of that at coastal locations. A maximum secondary organic aerosol concentration of 6.8 μg m −3 is predicted for Claremont, CA, during this episode. On a daily average basis at Claremont about 46% of this secondary organic aerosol is predicted to be a result of the oxidation of non-toluene aromatics (xylenes, alkylbenzenes, etc.), 19% from toluene, 16% from biogenic hydrocarbons (α-pinene, ß-pinene, etc.), 15% from alkanes and 4% from alkenes. The major uncertainties in predicting secondary organic aerosol concentrations are the reactive organic gas emissions, the aerosol yields and the partitioning of the condensable gases between the two phases. Doubling the reactive organic gas (ROG) emissions results in an increase of the secondary organic aerosol predicted at Claremont by a factor of 2.3. Predicted secondary organic aerosol levels are less sensitive to changes in secondary organic aerosol deposition and NO x emissions than to ROG emissions.