Polar Organic Compounds In PM_2.5 From The New Campus Of Sichuan Agricultural University In Ya'an

Polar organic compounds in atmospheric particulate matter have very important influences on atmospheric visibility,global climate and human health due to their strong hygroscopicity.The simultaneous presence of a large number of pollutants in the atmosphere can create complex interactions,resulting in complex atmospheric pollution.Secondary organic aerosols?SOA?have been the focus of attention,mainly because of its many hazards,such as harm to human health,affecting temperature distribution,and reducing visibility.In this paper,PM_2.5 samples were collected from June 2013 to June 2014 on the new campus of Sichuan Agricultural University in Ya'an City.Four types of polar organic compounds were identified by gas chromatography/mass spectrometry?GC/MS?,namely,SOA tracers,dicarboxylic acids,fatty acids and sugars/sugar alcohols.In addition,the possible sources and contributions of polar organic compounds to organic carbn?OC?in Ya'an atmospheric aerosols were discussed with other chemical component data,combined with air mass backward trajectory analysis,molecular marker tracing and principal component analysis.The results are as follows:?1?The annual average concentration of total isoprene SOA tracers in PM_2.5 of Ya'an was61.3±128 ng m^-3.The seasonal variation was shown as summer(168±210 ng m^-3)>autumn(49.9±73.2 ng m^-3)>spring(15.6±12.0 ng m^-3)>winter(9.80±8.03 ng m^-3).The annual average concentration of monoterpene SOA tracers and sesquiterpene SOA tracer??-caryophyllic acid?were 47.8±40.9 ng m^-3 and 1.84±2.03 ng m^-3,respectively.Their seasonal trends were similar and the higest occurred in winter(44.4±38.9 ng m^-3),followed by spring(35.6±15.3 ng m^-3),autumn(32.3±21.1 ng m^-3),and lowest in summer(20.8±20.3 ng m^-3).The concentration of anthropogenic?toluene?SOA tracer was 0.34±0.17 ng m^-3 with no significant variation in four seasons.The results of correlation analysis shows that there was a good correlation between tracers of anthropogenic and natural sources,indicating that anthropogenic pollutants may promote the formation of SOA of natural sources.?2?The annual average concentration of total diC₂-diC₁₃ was 394±231 ng m^-3,and the seasonal variation trend of total diC₂-diC₁₃ was spring(459±198 ng m^-3)>winter(436±332 ng m^-3)>autumn(348±182 ng m^-3)>summer(324±178 ng m^-3).The concentration of glyoxylic acid was the highest,followed by azelaic acid and succinic acid.In addition,malic acid,2-hydroxyglutaric acid and?o-,m-,p-?phthalic acid were also detected.Their annual average concentrations were 68.7±91.0,50.1±60.5 and 89.1±85.7 ng m^-3,respectively.Fatty acids(C₁₀-C₂₈)were the highest in all the analyzed species,with an annual average total concentration of3506±2783 ng m^-3,ranging from 353 to 18972 ng m^-3.Among them,hexadecanoic acid(C₁₆)and octadecanoic acid(C₁₈)were the two most abundant fatty acids.In addition,the contribution of long-chain fatty acids(C₂₀-C₂₈)from higher plant wax emissions was also remarkable.?3?The annual average concentration of total sugar/sugar alcohols was 380±168 ng m^-3,their total concentration in four seasons was spring 426±173 ng m^-3,summer 301±138 ng m^-3,autumn 319±167 ng m^-3 and winter 472±138 ng m^-3,respectively.The annual average concentration of anhydrosugars was 209±126 ng m^-3,which was 236±81.6 ng m^-3 in spring,98.1±76.5 ng m^-3 in summer,189±131 ng m^-3 in autumn and 320±108 ng m^-3 in winter.?4?Principal component analysis shows that the main sources of sugars/sugar alcohols in Ya'an were biomass combustion,biological emission and soil dust.The backward trajectory analysis shows that the atmosphere in Ya'an was mainly affected by the regional air mass in Sichuan Basin,which was consistent with its unique geographical environment.In addition,the air mass from long range transport also had certain influence on air quality in Ya'an.