Application Of Organic Aerosols Based On High Performance Single Particle Mass Spectrometry

Single Particle Mass Spectrometry（SPMS）is an instrument that can analyze the size and chemical compositions of individual particles in real-time.Many past studies have used SPMS to analyze aerosols in the environment,but the ability of SPMS to identify organic aerosols is low,which restricts the application of SPMS in the fields of organic aerosols.Thus,it is necessary to improve SPMS in order to further study organic aerosols.In recent years,SPAMS-0515 has made a lot of improvements in sampling systems,sizing system,ionization system and time-of-flight mass analyzer.In order to understand the Performance optimization of HP-SPAMS and its ability to identify organic aerosols,ambient air observation was carried out simultaneously with HP-SPAMS and SPAMS-0515 in this study.The results show that compared with SPAMS-0515,the sampling flow rate of HP-SPAMS is increased by 5 times（0.51 l/min）,and the sizing range is increased from 200-2500nm to 150 nm-3500nm,the sizing speed is increased by 25 times（up to 500p/s）,the particle hit rate is increased to 90%（3.6 times）,resolution increased to 2000（4 times）,and the signal acquisition range is expanded to 0.01-20v（40 times）.In addition,the ability of HP-SPAMS to identify aerosol particles was significantly enhanced,and can accurately identify ion signal peaks of oxalic acid and polycyclic aromatic hydrocarbons（PAHs）in organic aerosol.Considering the importance of organic aerosol to the environment,further use of HP-SPAMS to analyze the single particle information of oxalic acid and PAHs with high time resolution is expected to provide a method to detect organic aerosol in the atmosphere.Oxalic acid is an important dicarboxylic acid in the atmospheric environment.It can form oxalic acid-metal complexes with various non-hygroscopic polyvalent metals,and has an important impact on biological health and the atmospheric environment.Oxalic acid can potentially react with heavy metals（HMs）,however,the single particle mixing state of oxalate-metal complexes is still unclear.In this study,HP-SPAMS was used to investigate the size and chemical compositions of individual oxalate-containing HMs（i.e.,Fe,Cu,Pb,and Zn）in autumn in Nanjing.The results showed that higher number fractions of oxalic acid were observed in HMs（29.88%）,compared with all detected particles（17.16%）.Nfs of oxalic acid in each type of HMs were 20.84%（Fe）,45.59%（Cu）,37.16%（Pb）and 36.51%（Zn）.This phenomenon was probably attributed to the formation of oxalate-HMs complexes in the atmosphere,which was supported by the correlation between oxalic acid and Cu（r=0.53）,Pb（r=0.55）,and Zn（r=0.79）.Notably,the correlation between Fe and oxalic acid was significantly different during the daytime（r=0.29）and nighttime（r=0.71）,which was explained by the photochemical degradation of Fe-oxalate complexes and the Fe-driven Fenton reactions in the daytime.Besides,aerosol relative acidity and ambient relative humidity also affect the formation of oxalate-HMs complexes.Relative acidity is more likely to inhibit the formation of complexes.When relative humidity>70%,the increased relative humidity may promote the formation of oxalate-HMs complexes.This study provides more comprehensive insights into the enhanced oxalic acid formation in HMs and improves our understanding of the sink of oxalic acid in the atmosphere.PAHs and its derivatives are common organic air pollutants,most of which are mutagenic and carcinogenic,may be involved in long-term health effects,and are considered as a potential factor affecting the environmental health.Although most past studies have analyzed chemical reactions of PAHs in the environment,the influence of atmospheric oxidants on the formation of PAHs is still under debate.In this study,HP-SPAMS was used to investigate the size and chemical compositions of individual PAHs in autumn in Qingdao.The results showed that there was a good correlation（r²=0.860）between PAHs and Nitrate.Compared with all detected particles,the average diurnal variation trend of the peak area of the Nitrate-containing PAHs particles was significantly different,which may be because Nitrate can promote the transformation of PAHs particles to polycyclic aromatic hydrocarbon derivatives（NPAHs）through the nitration reaction.Furthermore,the average daily trend of number fractions variation of PAHs particles is significantly different from that of O₃ concentration,because in addition to the effect of photochemical reactions,O₃ also oxidized and degraded PAHs particles and promoted the generation of polycyclic aromatic hydrocarbon derivatives（OPAHs）.In addition,the influence of environmental factors relative humidity and relative acidity on PAHs particles was also analyzed.In addition,the effects of environmental factors relative humidity and relative acidity on PAHs were also analyzed.Both relative humidity（>70%）and relative acidity enhancement may promote the transformation of PAHs into PAH derivatives.