2013 Progress Report: The Role of Oxidation of BVOCs in SOA Production in the Southeastern U.S.EPA Grant Number: R835409
Title: The Role of Oxidation of BVOCs in SOA Production in the Southeastern U.S.
Investigators: Bertman, Steve , Pratt, Kerri A , Seeley, John , Shepson, Paul , Starn, Tim
Institution: Western Michigan University , Oakland University , Purdue University , West Chester University of Pennsylvania
EPA Project Officer: Hunt, Sherri
Project Period: April 1, 2013 through March 31, 2015 (Extended to March 31, 2016)
Project Period Covered by this Report: April 1, 2013 through March 31,2014
Project Amount: $387,483
RFA: Anthropogenic Influences on Organic Aerosol Formation and Regional Climate Implications (2012) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Global Climate Change , Climate Change , Air
The main activity of this project was to conduct field measurements of anthropogenic and biogenic volatile organic compounds and their oxidation products, including organic nitrate compounds, at the Southern Oxidant and Aerosol Study (SOAS) campaign during the summer of 2013. The goals are to understand the interactions between anthropogenic and biogenic emissions in the formation of secondary organic aerosol (SOA) and organic nitrates and the role that organic nitrogen compounds play in SOA formation. The significance of isoprene-nitrate radical reactions to secondary organic aerosol formation will also be evaluated using the EPA Community Multiscale Air Quality (CMAQ) model, comparing simulations to field measurements.
This project is proceeding successfully on schedule. The goals of the project have not changed from the original application. We deployed several field measurements (PANs, monoterpenes, isoprene nitrates, filter samples) during SOAS 2013 at the Centreville, AL, ground site in collaboration with many other research groups in support of the overall goals of SOAS and in pursuit of specific questions about the involvement of nitrogen chemistry in aerosol formation from BVOC. All instruments were in the field and operational by June 1, 2013, and continued to record data until the end of the mission on July 15, 2013. Following is a short list of activities undertaken as part of this project during the field study.
PAN was found to be ubiquitous with average levels lower than previous studies of PAN in the southeastern United States made in the 1990s. This is consistent with the decrease in NOx emissions experienced in the United States over the ensuing period. Organic nitrates were most elevated when air originated from north of the site and when there was evidence of local/regional biomass burning. A clear diurnal profile for organic nitrate compounds suggests that boundary layer dynamics consistently influenced gas phase atmospheric composition at the surface of this site. Both PANs and isoprene nitrates consistently showed maxima in the late morning with minima achieved before sunrise. This dataset of organic nitrates along with a vegetation survey accomplished to estimate BVOC emissions should allow us to improve the modeling capabilities for these BVOC-derived photoproducts and contribute to the understanding of the role they play in SOA formation. Better understanding will allow more accurate predictions of SOA formation under varying environmental conditions, which will help constrain the particulate contribution to radiative forcing and climate change.
Alpha-pinene was the dominant monoterpene (MT) throughout the campaign, followed by beta-pinene. Unlike the organic nitrate photoproducts, MT concentrations peaked in the early morning and reached their minima in the late afternoon. Strong correlations between compounds were observed, not surprisingly. Individual monoterpene mole ratios ranged between 1 ppt and 4 ppb while isoprene mole ratios ranged from 0.05 to 10 ppb. The calculated production rate of SOA from the individual monoterpenes rivaled or exceeded that from isoprene.
Analysis of the data is ongoing.
The second year of the project will be spent on (a) chemical analysis of filter samples, (b) evaluation of the new sampling system, (c) analysis of field data, and (d) preparation of presentations/publications.