Proteinaceous Matter in PM 2.5 in Suburban Guiyang, Southwestern China: Decreased Importance in Long-Range Transport and Atmospheric Degradation

摘要

Proteinaceous matter (PrM) is a substantial constituent in bioaerosols. However, the sources and atmospheric processes of PrM remain large uncertainties. The characterizations, sources, and potential atmospheric processes of free amino acids (FAAs) and combined amino acids (CAAs) were investigated via a set of 1-year fine particle (PM2.5) samples collected in suburban Guiyang (a hilly basin area in Southwest China). The annual average concentrations of FAAs and CAAs were 156.31 +/- 41.52 and 315.36 +/- 147.66 ng m(-3), respectively. The dominant FAA and CAA species were proline, which was different from previous observations with glycine as a major species. The results indicated that the sources or atmospheric processes of aerosol PrM at this study site were different from previous observations in the urban and suburban areas. The analysis of AA-nitrogen isotope compositions and air mass back trajectories suggested that the abundances of aerosol FAAs and CAAs were highly controlled by primary sources (particularly plants) with less impact from long-range transport. Furthermore, the contributions of PrM degradation by ozone- and hydroxyl radical-related processes to total FAAs were found to be minor. The overall results suggested that the long-range transport and atmospheric degradation of PrM were insignificant factors affecting aerosol PrM abundance in this suburban area with the weak atmospheric oxidation capacity, high cloud cover rate, and frequent precipitation. Thus, the findings improve our understanding of the sources and atmospheric processes of aerosol PrM. Plain Language Summary Aerosol proteinaceous matter (PrM) consists of free amino acids (FAAs) and combined amino acids (CAAs). It is well documented that FAAs and CAAs have a large variety of natural sources. Moreover, the atmospheric degradation of CAAs has been regarded as a new potential source of aerosol FAAs. However, the relative contribution of primary and secondary sources to FAAs remains poorly understood. Based on a 1-year investigation of PrM in PM2.5 collected in suburban Guiyang (a hilly basin area in Southwest China), we found that proline was the dominant species in both FAAs and CAAs. This result was different from previous observations with glycine as a major species. Further, our analysis showed that aerosol PrM in this hilly basin area was mainly derived from local primary sources (particularly plants) with less influence from long-range transport of PrM. Moreover, the contribution of oxidative degradation of PrM to total FAAs was found to be minor. In general, the long-range transport and atmospheric degradation of PrM have an insignificant contribution to aerosol PrM abundance in this hilly basin area. Our findings provide new insights into the sources and atmospheric transformation of aerosol PrM.