Is Alaska Truly the Great Escape from Air Pollution? - Long Term Source Apportionment of Fine Particulate Matter in Fairbanks, Alaska

ABSTRACT

Alaska is generally considered to be a place that is one of the last great escapes from air pollution. However, they have not spent a winter in Fairbanks or the nearby village of North Pole, where the daily average PM_2.5 concentration was 170 µg/m³ in December 2012 according to the Alaska Department of Environmental Conservation (DEC) Air Monitoring Network. In this study, source apportionment using Positive Factorization Matrix (EPA PMF 5.0) has been conducted based on the 2005 to 2012 Fairbanks PM_2.5 compositional data including elements, sulfate, nitrate, ammonia, elemental carbon (EC), and organic carbon (OC) from the U.S. Environmental Protection Agency speciation network. Seven sources were identified: soil, gasoline, sulfate, diesel, wood smoke, road salt, and nitrate. The average contributions to PM_2.5 of these seven sources were 3.4%, 16.3%, 19.5%, 14.3%, 40.5%, 1.5%, and 4.5%, respectively. Wood smoke provided the highest contributions to PM_2.5. Its contributions were the lowest in 2007 (3.5 µg/m³) and peaked in 2009 (5.7 µg/m³). The winter contributions of sulfate, nitrate, diesel, road salt, and wood smoke were all substantially higher compared to other seasons. Wood smoke is the only source with weekend’s contribution greater than the weekdays’ corresponding to the times when residential wood combustion is more likely to occur. The contributions of diesel, wood smoke, and sulfate were approximately doubled on violation days (daily average PM_2.5 higher than 35 µg/m³) compared to all days. This finding indicates that winter heating is the most important factor affecting the air quality in Fairbanks. In the future, additional source apportionment using other receptor models and tracers will need to be conducted to confirm these results.