Date of Award
Doctor of Philosophy
Dr. Steven Bertman
Dr. John Miller
Dr. Andre Venter
Dr. Todd Barkman
Biogenic volatile organic compounds (VOC), including isoprene and terpenes, impact atmospheric processes such as production of tropospheric ozone, formation and growth of secondary organic aerosol (SOA), global climate change, and human health. Although estimated emission rates of total biogenic VOC exceed anthropogenic emissions, there are many challenges to direct measurements because they are very reactive with atmospheric oxidants and some are still difficult to detect by current analytical techniques. Therefore, high uncertainties lead to discrepancies between individual and total biogenic VOC budget with atmospheric oxidants and an underestimation of SOA formation.
White pine (Pinus strobus) was once a dominant species in many parts of the Great Lakes region and is currently growing back. To estimate future air quality in light of Midwest forest succession, the composition of terpenes in white pine needles was analyzed over five growing seasons at the University of Michigan Biological Station and other forests in Michigan using gas chromatography with mass spectrometric detection. Early successional trees were selectively girdled in one forest in 2008, and the successional influence on total terpene concentration in this forest was observed by 2011. Terpene composition in pine needles displays chemotypic variation within forests at the molecular biology level and has the potential to affect atmospheric chemistry. α-Pinene was the dominant terpene in white pine and accounted for 30-50% of all terpenes on a mole basis. However, 14% of the trees showed high levels of a single enantiomer of limonene in the same specific trees every year. The limonene contribution to hydroxyl radical reactivity was estimated to be approximately 4% higher than without consideration of chemotypic differences, which may be derived from genetic differences.
Peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), and peroxymethacryloyl nitrate (MPAN), photooxidation products of VOC in the presence of nitrogen oxides (NOx), were measured during the Southern Oxidation and Aerosol Study (SOAS) field campaign in Alabama in summer 2013 using GC-ECD. The measured levels were lower than in past ground measurements in the southeast, with daytime means of PAN: 169, PPN: 5, and MPAN: 9 parts per trillion volume. Higher levels were seen in air influenced by urban sources. A multiple regression analysis indicates that biogenic VOC can account for 66% of PAN formation over the campaign. MPAN, which is derived solely from isoprene, is more strongly correlated to isoprene nitrates than to its precursor methacrolein, which indicates the possibility of an unreported atmospheric mechanism for formation of MPAN. This work reports the first relationship between gas-phase MPAN and organic particles from field measurements. The highest levels of MPAN correlate well with high levels of total organic mass in particles (R2=0.455). In addition, chamber experiments of isoprene photooxidation in the presence of NOx showed a significant amount of a PAN-type compound identified as peroxyacryloyl nitrate (APAN), which is typically described as an anthropogenic product. APAN may assist in particle growth like MPAN.
Restricted to Campus until
Toma, Shino, "Chemotypic Variation of Biogenic Volatile Organic Compounds in Midwest Forest and Atmospheric Role of Peroxyacyl Nitrates in Southeastern U.S." (2017). Dissertations. 3124.