Measurement report: Characterization of sugars and amino acids in atmospheric fine particulates and their relationship to local primary sources

Abstract

Abstract. Sugars and amino acids are major classes of organic components in atmospheric fine particles and play important roles in atmospheric processes. However, the identification of their sources in different regions is explored little. To characterize local primary sources (biomass burning, plant, and soil sources) and evaluate their contributions to the total sugar compound and amino acid (AA) pool in different regions, fine particulate matter samples were collected from the urban, rural, and forest areas in Nanchang, China. The concentrations and compositions of sugar compounds (anhydrosugars, primary sugars, and sugar alcohols), free amino acids (FAAs), and combined amino acids (CAAs) were analysed by gas chromatography–mass spectrometry (GC-MS) after silylation derivatization. Urban areas had significantly higher average Σ sugar concentration (317±139 ng m−3) than that of the rural (181±72 ng m−3) and forest (275±154 ng m−3) areas (p<0.05). Overall, the distribution pattern of sugar compounds and CAAs in PM2.5 was generally similar in three areas. Levoglucosan accounted for 24.4 %, 22.0 %, and 21.7 %, respectively, of the total sugar pool in the urban, rural, and forest areas. This suggests that plant and soil sources, as well as biomass burning (BB), provide important contributions to aerosol sugars and CAAs in three areas. In the urban area, the concentrations of anhydrosugars showed a positive correlation with combined Gly concentrations, but no correlation was found between these two compounds in the rural and forest areas, indicating that the urban area is mainly affected by local combustion sources. This conclusion was also supported by the positive correlation between levoglucosan and non-sea-salt potassium, only observed in the urban area (Lev=0.07 K++37.7,r=0.6,p<0.05). In addition, the average levoglucosan / mannosan (L/M) ratio in the urban area (59.9) was much higher than in the rural (6.9) and forest areas (7.2), implying BB aerosols collected in the urban area originated from lignite burning, while the type of biofuels used in the rural and forest areas is mainly softwood. The concentrations of sugar alcohols in the rural and forest areas were positively correlated with that of CAAs, which are abundant in the topsoil (r=0.53∼0.62,p<0.05), suggesting that the contribution of local topsoil sources is large in these two areas. In the rural and forest areas, the concentrations of primary sugars were positively correlated with those of combined CAA species abundant in local dominant vegetation. Our findings suggest that combining specific sugar tracers and chemical profiles of CAAs in local emission sources can provide insight into primary source characteristics, including the types of biofuels burned, the contribution of topsoil sources, and local vegetation types.