A study of isoprene and its oxidation products via mass spectrometry, field studies, and modeling
Abstract
Isoprene has been shown to be an important precursor in the production of tropospheric ozone. High quality isoprene measurements are important as isoprene is the dominant reactive VOC at many rural sites and even some urban environments. The focus of my graduate research was on the measurement, study, and analysis of isoprene chemistry. A fast-time quadrupole ion trap (QIT) chemical ionization MS/MS method was developed to determine isoprene in the ambient atmosphere. This method was deployed at the University of Michigan Biological Station during the 1998 Program for Research on Oxidants: Photochemistry, Emissions, and Transport (PROPHET) study. During PROPHET an informal intercomparison of 5 on-line isoprene methods was conducted. This study revealed limitations of the sampling method for the QIT and demonstrated that the GC/MS techniques are robust and provide the lowest limits of detection for the determination of isoprene. A GC/MS method was deployed at the 1999 Southern Oxidants Study (SOS) to determine isoprene and isoprene's oxidation products: methyl vinyl ketone, methacrolein, and 3-methyl furan. Subsequently, the SOS data was combined with data from three other field sites to demonstrate the NOx dependence of isoprene-OH oxidation. A steady-state HOx model was used to provide estimates of ambient oxidant levels for the isoprene chemistry analysis. This study showed that the isoprene measurement data did follow a NOx dependence. Also, the isoprene-OH oxidation is most efficient at producing ozone at NOx concentrations greater than 2 ppb NO x.
Degree
Ph.D.
Advisors
Shepson, Purdue University.
Subject Area
Analytical chemistry|Atmosphere|Biogeochemistry
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