Speciation and trends of organic nitrogen in southeastern U.S. fine particulate matter (PM2.5)

Abstract

The impacts of meteorology and air quality on the concentrations and relative distributions of free and combined amino acids (FAA; CAA) are evaluated during a month-long sampling campaign at a semiurban site in the southeastern U.S. The average FAA concentration in fine aerosols (PM2.5) was 11 ± 6 ng m-3, while CAA was found to be several times higher at 46 ± 21 ng m-3. Glycine and alanine were the most abundant amino acids, accounting for 48% of FAA and 58% of the CAA, while distinct differences were observed in compound distributions; glutamic acid, aspartic acid, serine, and threonine accounted for a further 29% of FAA and 30% of the total CAA. An intense rainfall event during the campaign demonstrated the significant impact of meteorological and air quality conditions on FAA-CAA concentrations and distributions. Correlative trends with atmospheric oxidant (ozone) and inorganic nitrogen levels suggest an important role for atmospheric processing. The liquid chromatography-mass spectrometry (quadrupole time-of-flight) technique used in this study allowed for detection of coextracted water-soluble organic compounds and characterization of a larger fraction of the organic nitrogen mass. N-heterocyclic compounds were detected in samples from this campaign, indicating a likely biomass burning source contribution for organic nitrogen. Key PointsFree and combined amino acids (FAA; CAA) in aerosols (PM2.5) are investigatedResults are linked with meteorology, ozone levels, and inorganic N trendsAtmospheric processing plays an important role in understanding speciated ON © 2012. American Geophysical Union. All Rights Reserved.