Levels, Source And Transformation Of Amino Acids In PM_2.5 In Forest Areas Of Nanchang

Proteinaceous matters（combined amino acids and free amino acids）are an importantfraction of organic nitrogen compounds which have a significant impact on the global climate,nitrogen cycle and human health,so it is of great significance to carry out research on this.This study collected and studied atmospheric aerosol fine particulate matter(PM_2.5)sampling in the forest area during spring in Nanchang.The concentrations and isotope of combined amino acids（CAAs）and free amino acids（FAAs）in PM_2.5were determined by derivatization mass spectrometry（GC-MS-IRMS）,respectively.In addition,combined with organic matter concentration data,meteorological data,and gaseous pollutant data,using correlation analysis,air mass backward trajectory analysis,PSCF and nitrogen isotope tracing technology determined CAAs and FAAs in PM_2.5during spring in Nanchang forest area.The aims of this study were to investigate the characteristics of amino acids including essential characteristics,and their sources and atmospheric chemical processes in forest aera.The major results showed as follows:（1）The concentration of CAAs（2212.6±1399.0 pmol/m³）in PM_2.5 in forest area was apparently higher than that of FAAs（213.7±131.4 pmol/m³）.The concentration of amino acids in this area was much lower than that in urban areas,higher than the concentration of amino acids in marine areas,and similar to observation level in rural areas.（2）The major constituents of CAAs in PM_2.5 in forest area were mainly proline,glycine,glutamic acid,leucine and alanine,accounted for 18.3±10.0%,16.8±10.4%,14.3±4.6%,12.0±4.5%and 8.6±1.7%of the total CAAs;and glycine was the most dominant amino acid in the composition profiles of FAAs,accounted for 71.1±9.3%of the total FAAs.In addition,the percentage of neutral amino acids in free amino acids（85.6%）was significantly higher than that in combined amino acids（42.6%）which may be related to the photochemical reaction of amino acids during long-distance transmission.（3）This study was further confirmed that high molecular weight protein substances could be degraded into low molecular weight amino acids under the action of atmospheric oxidant（O₃）in the PM_2.5in the forest area.In addition,this study found that high temperature could promote the enzymatic or photocatalytic hydrolysis of high-molecular-weight protein substances in aerosols,while precipitation could reduce the concentration of amino acids in aerosols,indicating that the meteorological conditions and atmospheric oxidation capacity will affect the concentration of amino acids in aerosols.（4）Backward trajectory clustering and PSCF results showed that the amino acids in atmospheric aerosols in forest area was mainly contributed by local sources,while the impact of long-range transport was relatively small.In addition,correlation analysis results showed that the sources of amino acids in aerosols in forest areas were mainly microbial activities and soil emissions.（5）Combined with stable isotope technology,it was found that the amino acids in PM_2.5in forest area were mainly affected by natural source.