EXPERIMENTAL OBSERVATIONS OF NON-METHANE HYDROCARBONS AND NOX SOURCES IN URBAN AND RURAL LOCATIONS
Wallace, Henry William
MetadataShow full item record
Non-methane hydrocarbons (NMHCs) and NO + NO2 (NOx) are precursors for photochemical smog which includes particulate matter and ozone. NMHCs and NOx have both biogenic and anthropogenic sources. This work characterizes sources of NMHCs and NOx by developing and deploying instrumentation for the quantification of NMHCs emitted from vegetation and spark ignition engines. A two channel volatile organic compound (VOC) preconcentration system was designed and constructed to measure C2 to C12 VOCs with a gas chromatograph-ion trap mass spectrometer GC-ITMS and a gas chromatography-flame ionization detector. Observations from three field experiments are used to characterize sources of VOC and NOx, and the impact these pollutants have on local air chemistry. Focus is given to mobile sources emissions as they are an important, often dominant, source of NHMCs and NOx in urban environments. Morning rush hour CO to NOx ratios of 4.2 ± 0.59 mol/mol and 6.9 ± 1.1 mol/mol are reported for Boise, ID and Sacramento, CA, respectively. VOC to CO ratios for both Boise, ID and Sacramento, CA are reported as well. Toluene to CO ratios during the morning rush hour were observed at 2.4 ± 0.04 nmol/mol in Boise, ID and 4.7 ± 0.34 nmol/mol in Sacramento, CA while benzene to CO was 1.3 ± 0.02 nmol/mol and 1.1 ± 0.05 nmol/mol in Boise, ID and Sacramento, CA, respectively. A thorough evaluation of the US EPA’s vehicle emissions models MOBILE6.2 and MOVES is presented. The analysis shows that MOVES represents a significant improvement over MOBILE6.2. The preconcentration system was used quantify VOCs emissions from automobiles in an urban environment. Emissions measured from mobile sources are compared to predicted values from the models and the MOVES model was found to greatly improve the prediction of CO to NOx when compared to the older MOBILE6.2 model. Biogenic sources of VOCs and NOx are examined in a rural location using a profiling sample inlet to spatially resolve chemical gradients in a forest. Evidence of mixing in the canopy has been explored using the Leighton relationship and the gradients presented can be analyzed to determine sources and sinks in the canopy.