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Sources and composition of PM 2.5 in the Colorado Front Range during the DISCOVER‐AQ study
Author(s) -
Valerino M. J.,
Johnson J. J.,
Izumi J.,
Orozco D.,
Hoff R. M.,
Delgado R.,
Hennigan C. J.
Publication year - 2017
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2016jd025830
Subject(s) - aerosol , particulates , air quality index , environmental science , range (aeronautics) , chemical composition , atmospheric sciences , environmental chemistry , front (military) , air mass (solar energy) , nitrate , organic matter , chemistry , hydrology (agriculture) , meteorology , geography , geology , physics , geotechnical engineering , materials science , organic chemistry , boundary layer , composite material , thermodynamics
Measurements of particulate matter (PM 2.5 ) chemical composition were carried out in Golden, CO, during the Deriving Information on Surface Conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER‐AQ) field study. Chemical composition was dominated by organic compounds, which comprised an average of 75% of the PM 2.5 mass throughout the study. Most of the organic matter was secondary (i.e., secondary organic aerosol) and appears to derive predominantly from regional sources, rather than the Denver metropolitan area. The concentration and composition of PM 2.5 in Golden were strongly influenced by highly regular wind patterns and the site's close proximity to the mountains (~5 km). This second factor may be the cause of distinct differences between observations in Golden and those in downtown Denver, despite a distance between the sites of only ~15 km. Concentrations of aerosol nitrate, ammonium, and elemental carbon increased significantly during the daytime when the winds were from the northeast, indicating a strong local source for these compounds. Local sources of dust appeared to minimally impact the Golden site, although this was not likely representative of other conditions in the Colorado Front Range. Conversely, dust that had undergone long‐range transport from the southwestern U.S. likely impacted the entire Colorado Front Range, including Golden. During this event, water‐soluble Ca 2+ concentrations exceeded 1 µg m −3 , and the PM 2.5 /PM 10 ratio reached its lowest level throughout the study. The long‐range transport of wildfire emissions also impacted the Colorado Front Range for 1–2 days during DISCOVER‐AQ. The smoke event was characterized by high concentrations of organics and water‐soluble K + . The results show a complex array of sources, and atmospheric processes influence summertime PM in the Colorado Front Range.