MATHEMATICAL-MODELING OF URBAN ORGANIC AEROSOL - PROPERTIES MEASURED BY HIGH-RESOLUTION GAS-CHROMATOGRAPHY

Primary fine aerosol emissions from a variety of urban sources have be en quantitatively characterized via high-resolution gas chromatography to obtain organic mass distribution fingerprints. To assess the degre e of secondary organic aerosol formation in urban areas, a transport m odel is used to predict the distribution of ambient organic aerosol ch aracteristics that would exist at various sites in the Los Angeles Bas in if the primary organic emissions were transported without chemical reaction. Comparisons between the model predictions and ambient measur ements show substantial agreement for the nonpolar organics, suggestin g that ambient concentrations of this organic fraction result directly from primary emissions. In contrast, ambient concentrations of fine a cidic organic aerosols are significantly underpredicted by the model, indicating that secondary formation is important for acidic organics. On the basis of the observed differences between model predictions and measured properties of acidic organics, it is estimated, using monthl y averages, that up to 18-27 % of the elutable organic aerosol present in the Los Angeles atmosphere may be secondary in origin.