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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 5 | Copyright
Atmos. Chem. Phys., 18, 3701-3715, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 13 Mar 2018

Research article | 13 Mar 2018

Ubiquitous influence of wildfire emissions and secondary organic aerosol on summertime atmospheric aerosol in the forested Great Lakes region

Matthew J. Gunsch1, Nathaniel W. May1, Miao Wen2, Courtney L. H. Bottenus2,3, Daniel J. Gardner1, Timothy M. VanReken2,a, Steven B. Bertman4, Philip K. Hopke5,6, Andrew P. Ault1,7, and Kerri A. Pratt1,8 Matthew J. Gunsch et al.
  • 1Department of Chemistry, University of Michigan, Ann Arbor, MI, USA
  • 2Department of Civil and Environmental Engineering, Washington State University, Pullman, WA, USA
  • 3Pacific Northwest National Laboratory, Richland, WA, USA
  • 4Department of Chemistry, Western Michigan University, Kalamazoo, MI, USA
  • 5Center for Air Resources, Engineering and Science, Clarkson University, Potsdam, NY, USA
  • 6Department of Public Health Sciences, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA
  • 7Department of Environmental Health Sciences, University of Michigan, Ann Arbor, MI, USA
  • 8Department of Earth and Environmental Science, University of Michigan, Ann Arbor, MI, USA
  • anow at: National Science Foundation, Alexandria, VA, USA

Abstract. Long-range aerosol transport affects locations hundreds of kilometers from the point of emission, leading to distant particle sources influencing rural environments that have few major local sources. Source apportionment was conducted using real-time aerosol chemistry measurements made in July 2014 at the forested University of Michigan Biological Station near Pellston, Michigan, a site representative of the remote forested Great Lakes region. Size-resolved chemical composition of individual 0.5–2.0µm particles was measured using an aerosol time-of-flight mass spectrometer (ATOFMS), and non-refractory aerosol mass less than 1µm (PM1) was measured with a high-resolution aerosol mass spectrometer (HR-AMS). The field site was influenced by air masses transporting Canadian wildfire emissions and urban pollution from Milwaukee and Chicago. During wildfire-influenced periods, 0.5–2.0µm particles were primarily aged biomass burning particles (88% by number). These particles were heavily coated with secondary organic aerosol (SOA) formed during transport, with organics (average O∕C ratio of 0.8) contributing 89% of the PM1 mass. During urban-influenced periods, organic carbon, elemental carbon–organic carbon, and aged biomass burning particles were identified, with inorganic secondary species (ammonium, sulfate, and nitrate) contributing 41% of the PM1 mass, indicative of atmospheric processing. With current models underpredicting organic carbon in this region and biomass burning being the largest combustion contributor to SOA by mass, these results highlight the importance for regional chemical transport models to accurately predict the impact of long-range transported particles on air quality in the upper Midwest, United States, particularly considering increasing intensity and frequency of Canadian wildfires.

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During summer 2014, atmospheric particulate matter in northern Michigan was impacted by wildfire emissions under all air mass conditions (Canadian wildfires, US urban, and Canadian forest influences). Biomass burning particles coated with secondary organic aerosol contributed the majority of the submicron aerosol mass. Given increasing wildfires, the impacts of biomass burning on air quality must be assessed, particularly for downwind areas impacted by long-range transport.
During summer 2014, atmospheric particulate matter in northern Michigan was impacted by wildfire...