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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. Citation: Samy, S., J. Robinson, I. C. Rumsey, J. T. Walker, and M. D. Hays (2013), Speciation and trends of organic nitrogen in southeastern U. S. fine particulatematter (PM2.5), J. Geophys. Res. Atmos., 118, 1996-2006, doi: 10.1029/2012JD017868.