Source attribution of ambient air toxic and other VOCs in Columbus, Ohio

Chemical mass balance (CMB) source apportionment modeling was conducted on a data set of 142 3 h integrated air samples collected at 6 different sites in 3 separate campaigns during the summer of 1989 in Columbus, Ohio; source contributions to 19 light hydrocarbon and toxic VOC species, including formaldehyde and acetaldehyde, were modeled. Overall, the results indicated that area sources, and in particular vehicle exhaust and organic solvent usage by small industrial/commercial facilities, are important contributors to the major toxic VOCs measured in urban air. In addition, the temporal resolution of the measurements allowed a number of observations regarding the short-term variability of these area sources, including diurnal trends in vehicle exhaust, gasoline vapor, and natural gas sources. The natural gas source was identified as a significant source of light hydrocarbons in the Columbus area, a finding similar to that of several other recent source apportionment studies of VOCs in urban areas. The temporal and spatial variability in gasoline vapor contributions suggested that the source is associated more with mobile sources (running losses, evaporative emissions from vehicles), rather than with fixed sites such as service stations. Finally, CMB modeled source contributions were coupled with a simple box model of the study area to provide estimates of the emission rates of various area sources. The results of these calculations suggest that there are probably substantial emissions from area sources that are not included in current emissions inventories.