AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Chemical Composition of PM2.5 in Zion, IL during the 2017 Lake Michigan Ozone Study (LMOS)
DAGEN HUGHES, Alissia Milani, Megan Christiansen, Dylan Millet, Timothy Bertram, Charles Stanier, Elizabeth Stone, University of Iowa
Abstract Number: 491 Working Group: Carbonaceous Aerosol
Abstract Ambient fine particulate matter (PM2.5) was collected during the Lake Michigan Ozone Study (LMOS) from May 21 to June 23, 2017 to identify the major PM2.5 sources affecting Zion, IL. PM2.5 mass concentration ranged from 1.4 – 12.9 µg/m3 and averaged 5.1 µg/m3 with elevated mass loadings coinciding with elevated ozone. The most significant contributor to PM2.5 mass was organic matter (OM, calculated as 1.7 x organic carbon (OC), contributing 61.8%), followed by sulfate (17.1%), ammonium (6.6%), nitrate (3.6%), and elemental carbon (EC, 3.6%). Elemental and organic tracers indicated that OM was influenced by vehicle emissions, biomass burning, and secondary organic aerosol (SOA) predominantly from isoprene. Isoprene-derived organosulfates accounted for 3.6% of OM on average, with methyltetrol sulfate being the most abundant. In comparison, organosulfates derived from monoterpenes and anthropogenic precursors accounted for 0.3% and 0.5% of OM, respectively. PM2.5 composition was compared between three episodes when hourly ozone exceeded 70 ppb and non-ozone periods. On June 2, ozone peaked at 91 ppb coincident with the highest PM2.5 mass loading and lowest OC:EC ratio (7.0), indicating a greater relative influence from combustion sources. From June 10-12, ozone peaked at 76 ppb and PM2.5 was heavily influenced by SOA formation as indicated by an OC:EC ratio of 17.9 and tenfold increase in methyltetrol sulfate. In contrast, isoprene SOA was relatively low from June 13-16 when ozone peaked at 88 ppb. These data demonstrate that anthropogenic and biogenic sources of PM2.5 organic carbon vary across periods of high ozone during LMOS. Molecular and elemental tracers will be used in positive matrix factorization to estimate PM2.5 source contributions to PM2.5, with an emphasis on evaluating the distributions of primary/secondary and biogenic/anthropogenic sources.