Atmospheric carbonyl compounds in rural and urban Texas: Formation, methodology, and statistical modeling
Friedfeld, Stephen Judah
Fraser, Matthew P.
Doctor of Philosophy
Atmospheric carbonyl compounds, specifically aldehydes and ketones, were measured in both rural and urban regions in Texas. The biogenic or rural study examined the extent of conversion from primary biogenic hydrocarbons to secondary carbonyls. The anthropogenic or urban studies investigated techniques for measuring carbonyl compounds; statistical modeling was applied in one such study to elucidate the primary and secondary contributions to formaldehyde formation. From the biogenic study, the spatial variation of isoprene and its reaction products' concentrations are strong functions of the immediate land cover. Spatial differences between sampling sites need to include NOx data to account for urban and rural influences. Finally, both ozone attributable to biogenic hydrocarbon oxidation and ozone formation potential are predicted to be insignificant under high VOC/NOx ratios typical of rural areas, but may be important under conditions where NOx levels are elevated. From the anthropogenic studies, a daylong sampling period sufficiently captures persistent low-lying carbonyl levels, but overlooks small scale fluctuations. Furthermore, the low concentration precision limit of real-time sampling through a DFG sensor produces similar bias as time-integrated wet chemical quantification, and validates the use of the DFG system for urban atmospheric studies. Finally, two distinct statistical models attribute nearly two-thirds (ratio 1.75) of HCHO formation to secondary VOC reactions, and one-third to primary emissions.
Geophysics; Environmental science