MATHEMATICAL-MODELING OF ATMOSPHERIC FINE PARTICLE-ASSOCIATED PRIMARYORGANIC-COMPOUND CONCENTRATIONS

An atmospheric transport model has been used to explore the relationsh ip between source emissions and ambient air quality for individual par ticle phase organic compounds present in primary aerosol source emissi ons. An inventory of fine particulate organic compound emissions was a ssembled for the Los Angeles area in the year 1982. Sources characteri zed included noncatalyst- and catalyst-equipped autos, diesel trucks, paved road dust, tire wear, brake lining dust, meat cooking operations , industrial oil-fired boilers, roofing tar pots, natural gas combusti on in residential homes, cigarette smoke, fireplaces burning oak and p ine wood, and plant leaf abrasion products. These primary fine particl e source emissions were supplied to a computer-based model that simula tes atmospheric transport, dispersion, and dry deposition based on the time series of hourly wind observations and mixing depths. Monthly av erage fine particle organic compound concentrations that would prevail if the primary organic aerosol were transported without chemical reac tion were computed for more than 100 organic compounds within an 80 km x 80 km modeling area centered over Los Angeles. The monthly average compound concentrations predicted by the transport model were compared to atmospheric measurements made at monitoring sites within the study area during 1982. The predicted seasonal variation and absolute value s of the concentrations of the more stable compounds are found to be i n reasonable agreement with the ambient observations. While model pred ictions for the higher molecular weight polycyclic aromatic hydrocarbo ns (PAH) are in agreement with ambient observations, lower molecular w eight PAH show much higher predicted than measured atmospheric concent rations in the particle phase, indicating atmospheric decay by chemica l reactions or evaporation from the particle phase. The atmospheric co ncentrations of dicarboxylic acids and aromatic polycarboxylic acids g reatly exceed the contributions that are due to direct emissions from primary sources, confirming that these compounds are principally forme d by atmospheric chemical reactions.