Molecular tracers for sources of atmospheric carbon particles : measurements and model predictions
Carbonaceous compounds are the largest contributor to the fine particulate matter in the atmosphere of urban areas. However, little is known about the concentrations, seasonal patterns, ambient chemical formation/destruction and source/receptor relationships that govern the individual compounds pres...
| Summary: | Carbonaceous compounds are the largest contributor to the fine particulate matter in the atmosphere of urban areas. However, little is known about the concentrations, seasonal patterns, ambient chemical formation/destruction and source/receptor relationships that govern the individual compounds present in this complex organic mixture. The objective of the present research is to characterize the particulate organic compounds present in source emissions and in ambient air and to use those data to evaluate methods for computing source contributions to ambient pollutant concentrations.
Airborne fine particulate matter samples collected at 4 urban sites within the Los Angeles basin during 1982 were analyzed by gas chromatography/mass spectrometry. More than 100 individual organic compounds were identified. Primary organic aerosol constituents including n-alkanes, n-alkanoic acids, polycyclic aromatic hydrocarbons, hopanes, and steranes reveal a seasonal pattern with high winter and low summer concentrations. Aliphatic dicarboxylic acids possibly formed by atmospheric reactions show a reverse pattern, with high concentrations in late spring/early summer.
Next, fine particulate emissions from major urban sources were characterized. The sources tested were responsible for more than 80% of the fine carbonaceous aerosol emitted to the Los Angeles atmosphere. The identification of organic compounds that act as markers for the presence of effluents from particular source types was emphasized. It was found that fossil petroleum compounds such as hopanes and steranes can be used to trace vehicular fine particulate emissions in the urban atmosphere, iso- and anteiso-alkanes are useful tracers for cigarette smoke, cholesterol is a likely tracer for meat smoke aerosol, C29 - C33 odd carbon number n-alkanes can be used to estimate airborne vegetative detritus concentrations, and certain resin acids can be used to track wood smoke aerosols.
The source emission data have been used along with an atmospheric transport model to calculate primary source contributions to the concentrations of single particle-phase organic compounds in the Los Angeles atmosphere. The predicted and measured concentrations of stable primary organic compounds agree well. This indicates that a nearly complete knowledge of source/receptor relationships for many particle-phase primary organic compounds has been achieved for the first time. The model predictions indicate that aliphatic dicarboxylic and aromatic polycarboxylic acids measured in the urban atmosphere are indeed the products of atmospheric chemical reactions.
|
|---|