Organic Tracer Analyses and Receptor Modeling of PM2.5 in Fairbanks, Alaska
Ambient particulate matter (PM) levels are of great importance to many areas around the world for both environmental and health concerns. It is well known that many sources of PM are anthropogenic in nature, including sources such as the combustion of petroleum products and wood. As per the Clean Air Act of 1970, the US EPA has established a National Ambient Air Quality Standard (NAAQS) of 35µg/m3 for a 24 hour average and 15µg/m3 for an annual average of ambient PM2.5 to improve the quality of air and reduce occurrences of respiratory illness resulting from exposure to high levels of PM2.5. Fairbanks, the largest city in the interior of Alaska, experiences harsh winters with prolonged temperature inversions and calm winds. Due to these factors, there is an accumulation of PM in the valley, resulting in regular violations of the 24 hour NAAQS during the winter and thus in the Fairbanks North Star Borough area being considered a nonattainment area for PM2.5 by the US EPA. Previous chemical mass balance (CMB) studies have shown that the majority of the Fairbanks wintertime PM2.5 is from residential wood combustion. But these CMB studies also identified a relatively high fraction (up to 20%) of sulfate of unspecified origin. The goal of this work is to paint a clearer picture of the sources of the PM2.5 problem in Fairbanks, AK with a focus on the potential sources of sulfate. This is achieved by quantifying select organic species (hopanes, steranes, picene, and thiophenes) in Fairbanks PM2.5. These compounds have been reported to be found in emissions from combustion of various fossil fuels. The measured chemical composition of Fairbanks PM2.5 is compared to reported composition for PM2.5 in other air sheds and to published source profiles. Several fuels received from Fairbanks were analyzed as well for the selected chemical markers in an effort to identify potential sources of these markers. Fairbanks PM2.5 was found to contain relatively high levels of all of the markers analyzed. Comparisons of the chemical composition of Fairbanks PM2.5 to other air sheds and to source profiles revealed that Fairbanks PM2.5 is heavily impacted from fossil fuel use. Thus, while it remains clear that Fairbanks PM2.5 is impacted predominantly by wood smoke from residential heating, it is now also clear that fossil fuel combustion is a major contributor. High levels of picene indicate a significant contribution of coal combustion, while high levels of thiophenes very likely indicate a significant contribution from no. 2 fuel oil combustion. High levels of select organo-sulfur compounds in no. 2 Fuel oil suggest that this fuel used in Fairbanks for residential heating and power production is very likely a significant source of the sulfate.
chemical mass balance, GC-MS, organic tracer, particulate matter, PM chemical marker, PM2.5, source apportionment
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