Comment on acp-2022-269

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 less explored. To characterize local primary sources (biomass burning, plant and soil sources) and evaluate their contributions to the total sugar compounds and AAs pool in different regions, fine particulate matter samples were collected from the urban, rural and forest locations. The concentrations and compositions of sugar compounds (anhydrosugars, primary sugars and sugar alcohols), free amino acids (FAAs) and combined amino acids (CAAs) were analyzed. Overall, the distribution pattern of sugar compounds and CAAs in PM2.5 was generally similar among the urban, rural and forest locations. Moreover, the average contribution of sugar compounds and CAAs reflecting BB, plant and soil sources to the total sugar and CAA pool were consistent in all sampling locations. These suggest BB, plant and soil sources all have important contributions to aerosol sugars and CAAs in three locations. 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, while the rural and forest areas may be more influenced by long-transport BB source. In addition, the average L/M ratio in the urban location (59.9) was much higher than those in the rural (6.9) and forest locations (7.2), implying BB aerosols collected in the urban location originated from lignite burning while the type of biofuels used in the rural and forest locations is mainly softwood. The concentrations of sugar alcohols in the rural and forest locations were positively correlated with that of CAAs, which are abundant in the topsoil, suggesting that the contribution of local topsoil sources is large in these two locations. In the rural area, the concentrations of primary sugars were positively correlated with that of combined aspartic acid (a CAA specie abundant in grass, the dominant vegetation in the rural area), while in the forest area, primary sugars had good correlations with combined citrulline, lysine, ornithine, glutamic acid and serine (CAA species abundant in pine, dominant vegetation in the forest area), indicating that combining primary sugars with major CAA species in local dominant vegetations may identify local vegetation types. Furthermore, the nitrogen isotope of combined Gly and PMF model results demonstrated that the average contribution of combustion processes to total sugar compounds and CAAs pool in the urban and rural locations was higher than that in the forest location while primary biogenic sources showed a higher average contribution in the forest location than those in rural and urban locations. Our findings suggest that combining specific sugar tracers and chemical profiles CAAs in local emission sources can provide insight to primary sources characteristics including the types of biofuels burned, the contribution of topsoil sources and local vegetation types.