Sources and Transformation Processes of Proteinaceous Matter and Free Amino Acids in PM2.5

Abstract

AbstractAmino acids is an important organic nitrogen compound class in aerosol. Its origins and transformation in the atmosphere remain poorly understood. The concentrations of free amino acids (FAAs) and combined amino acids (CAAs) and δ15N values of free and combined Glycine (Gly) in PM2.5 and main emission sources (plant, soil, and aerosol from biomass burning) were investigated from five sampling sites in Nanchang area (Jiangxi Province, China). Our results showed that the composition profiles of CAAs and FAAs were quite different from each other in PM2.5. For CAAs, percentages of individual combined amino acids were different between biomass burning sources and plant or soil sources, and we found that the composition profiles of aerosol CAAs could reflect the contribution of the main emission sources. For FAAs, a predominance of free Gly was observed in aerosol FAAs pool because atmospheric photooxidative processes could increase free Gly and decrease other reactive FAAs. This implied that the composition of aerosol FAAs could not reflect their origins. A strong correlation between δ15NF‐Gly values in aerosols or sources and the δ15NC‐Gly values in their parent CAAs was observed, indicating that the isotope effect associated with Gly transformation in aerosols may be small. Additionally, we found more positive δ15NGly in aerosols emitted by biomass burning, which was likely due to 15N‐depleted amino‐N loss from Gly molecule. The results suggested that δ15NGly values in aerosols might be used to identify biomass burning sources.