A study of the nitrates of volatile organic compounds
Abstract
The importance of p-xylene and isoprene with respect to tropospheric ozone chemistry was investigated through the study of the organic nitrates derived from these reactive VOCs. Through a series of experiments in a 5000 L photochemical reaction chamber in the Shepson laboratory, it was determined that 4-methylbenzyl nitrate was produced from the OH-initiated oxidation of p-xylene with a yield of 3.3%. Atmospheric isoprene nitrates were determined for the first time as part of this work utilizing an online Tenax-based preconcentration system followed by separation and analysis via GC-LND. This instrument was deployed at the University of Michigan Biological Station as part of the Program for Research on Oxidants: PHotochemistry, Emissions, and Transport (PROPHET) 1998 Summer Intensive field study. The instrument was also deployed during the summer of 1999 at the Southern Oxidants Study (SOS). At both field sites the absolute concentrations of the isoprene nitrates and their contribution to NOy were comparable to those of the observed simple alkyl nitrates. The difference in the absolute magnitudes of the isoprene nitrate concentrations from these two field studies was analyzed based on the NOx dependent chemistry of their formation. A steady state [HOx] calculation was employed to simulate the concentration of the important atmospheric oxidant OH, and assess the quality of the isoprene nitrate data sets. As a result of this analysis, the measurement data obtained at the two field sites were consistent, in that the production of isoprene nitrates is highly NOx dependent.
Degree
Ph.D.
Advisors
Shepson, Purdue University.
Subject Area
Analytical chemistry|Atmosphere|Environmental science
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