Dissolved hydrolyzed amino acids in precipitation in suburban Guiyang, southwestern China: Seasonal variations and potential atmospheric processes

Abstract

Proteinaceous compounds are particularly interesting because of their ubiquity and importance in many atmospheric processes. We investigated hydrolyzed amino acid (HAA), dissolved organic nitrogen (DON), nitrate (NO3−) and ammonium (NH4+) concentrations in precipitation samples collected in a suburban site in Guiyang over a 12 month period. Annually averaged total HAA, DON, NO3− and NH4+ concentrations were 3.7 μmol L−1, 151.1 μmol L−1, 68.9 μmol L−1 and 117.3 μmol L−1, respectively. Regarding the HAAs in precipitation, glutamic acid, glycine and proline were present in relatively high concentrations, followed by aspartic acid and alanine. The concentrations of total HAAs in precipitation showed a clear seasonal cycle, with a minimum level in winter and a maximum level in spring. Based on seasonal variations of total HAAs together with back-trajectory analysis, the air mass origins did not significantly impact the precipitation HAA levels. The NO3− concentrations recorded a better positive correlation (P < 0.01) with both the DON and total HAA concentrations than the NH4+ concentrations, possibly revealing that the sources for precipitation amino acids in suburban Guiyang were more linked with NO3− sources (from biomass burning, microbial activities and agricultural activities) than with NH4+ sources (from biomass burning and agricultural activities). In particular, in some specific periods, such as spring, abundant pollen releases may have been responsible for the relatively high precipitation amino acid concentrations. The average air temperature and the highest air temperature showed a positive correlation with the total HAA levels in precipitation. Clearly, the increase in precipitation total HAAs with higher air temperatures may indicate the enhanced temperature-induced degradation of high molecular weight atmospheric proteinaceous matter. Moreover, the volume-weighted precipitation glycine and total HAA levels were positively correlated with the product of atmospheric ozone and nitrogen dioxide, indicating that atmospheric proteinaceous matter may be inextricably bound up with both ozone- and nitrogen dioxide-related atmospheric processes. In conclusion, this study improves current knowledge on the origins and atmospheric processes of atmospheric proteinaceous compounds.