Journal Article
Atmospheric Chemistry and Physics, vol. 18, iss. 5, pp. 3701-3715, 2018
Authors
Matthew J. Gunsch, Nathaniel W. May, Miao Wen, Courtney L. H. Bottenus, Daniel J. Gardner, Timothy M. VanReken, Steven B. Bertman, Philip K. Hopke, Andrew P. Ault, Kerri A. Pratt
Abstract
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
0.5–2.0 µm particles was measured using an aerosol
time-of-flight mass spectrometer (ATOFMS), and non-refractory aerosol mass
less than 1 µm (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,
0.5–2.0 µm 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.
