Organic Carbon Speciation at Seney

This lovely vista was photographed from the top of the fire tower at Seney National Wildlife Refuge in the upper peninsula of Michigan.  Seney is one of two Class 1 areas in the Midwest RPO states where visibility is a protected resource (Isle Royale National Park is the other).  Because most visibility impairment is caused by fine particle pollution, we began a study in 2002 to collect particulate samples and analyze the organic fraction for a suite of chemical species that can be used as markers for various sources of organic carbon (gasoline- and diesel-fueled vehicles, wood burning, meat cooking, and other combustion processes).   Dr. Jamie Schauer and his graduate student Rebecca Sheesley of the University of Wisconsin-Madison are conducting the analysis, which will include data from monthly composite samples for the entire year and a subset of daily samples taken with a special high-volume sampler.  The resulting source apportionment will produce valuable information on the relative importance of anthropogenic and biogenic sources to visibility impairment in this scenic wilderness. 

Other measurements at Seney include ozone, speciated PM2.5 (through the IMPROVE network), light scattering (nephelometer), continuous PM2.5 (TEOM), meteorology, acid deposition (through the NADP network), and visibility (a camera records the scene from the fire tower every 15 minutes as part of the Midwest Haze Camera network)

In the plot at the left, the green portion of each bar represents the fraction of fine particles that is made up of organic carbon.   Over the entire year, OC makes up 25% of measured PM at Seney.  It peaks in the summer, which might be due to biogenic activity (terpene emissions from pine trees increase with sunlight and higher temperatures) or to increased emissions from anthropogenic sources and resulting photochemical reactions, or to a combination of both.  Ammonium sulfate and ammonium nitrate are also significant fractions of PM mass at Seney (47% and 19%, respectively).   High sulfate mass has been associated with air masses that come from the southern shore of Lake Erie, northern Ohio, and southern Lower Peninsula of Michigan.  High nitrate mass is associated with air flows from the southwest, including the Chicago/Milwaukee urban area and eastern Iowa.  High organic carbon days look similar to high sulfate days, with apparent influences from Chicago and Gary (see plot below).

Results of the speciated carbon analysis at Seney show that markers from primary emission sources are more prevalent during the winter months.  For example, the figure at left shows that hopanes, steranes and PAHs, which are associated with combustion of fossil fuels, are found primarily during cold weather.  Levoglucosan, a marker for biomass burning, is also found primarily in the winter with a smaller secondary peak in the summer.  In contrast, markers of secondary formation (e.g., the aromatic and aliphatic di- and tri-acids) peak in the summer, supporting the hypothesis that summer OC in this remote area is dominated by secondary formation.  Complete details on the Seney analysis are available in the draft report, Source Apportionment of Atmospheric Fine Particulate Matter Collected at the Seney National Wildlife Refuge, by Rebecca Sheesley and Jamie Schauer--contact Donna Kenski for a copy.