Component Analysis And Source Analysis Of Atmospheric PM_2.5 In The Suburbs Of Changzhou In Spring

To investigate the chemical compositions and pollution characteristics of spring fine particles(PM_2.5)in Changzhou,a total of 84 PM_2.5.5 samples were collected from March 1 to May 30,2017.We measured and analyzed and conventional components,such as water-soluble ions?WSIIs?,carbonaceous components?OC and EC?,Water-soluble organic acid,water-soluble organic carbon?WSOC?,water-soluble organic nitrogen?WSON?and n-alkanes.The water-soluble organic aerosol?WSOA?was also analyzed by an aerodyne soot particle aerosol mass spectrometer?SP-AMS?.Positive matrix factorization?PMF?model was utilized to analyze presumptive sources of PM_2.5 systematically and comprehensively at the sampling site,hoping to provide detailed data support for understanding and formulating countermeasures to air pollution in Changzhou.The main verdicts were as shown below:?1?During the sampling period,average daily PM_2.5 concentration was?101.97±35.45??g·m^-3,and no days were superior air quality.The number of days with good air quality were only accounting for 26.2%of the total days.The air quality during sampling period was dominated by light,moderate and heavy pollution,accounting for 39.3%,21.4%and 13.1%of the total days,respectively.More than 73.8%sampling days exceeded target-2 standard of the national ambient air quality standard of China,which showing that the air pollution in the suburbs was still at a high level.?2?The total WSIIs accounted for 39.9%of PM_2.5.5 mass,of which secondary ions(SO₄^2-,NH₄⁺and NO₃^-)accounted for 81.85%of total WSIIs.The slope of the linear fitted line of anion and cation charge balance?AE/CE?was 1.09,which indicated that PM_2.5.5 was weakly acidic.The average of OC/EC ratio was 2.53,indicating PM_2.5 was influenced by secondary conversion.Correlation analysis showed that carbonaceous components were mainly contributing by coal and gasoline vehicle exhaust emissions.WSOC accounted for 71.7%of the OC ratio,which was the major component of the OC.Water soluble total nitrogen?WSTN?which in the particles was mainly existed in the form of WSIN?mainly NH₄NO₃?,while WSON only accounted for 12.9%of WSTN.Simultaneously,it was detected that PM_2.5contained formic acid and oxalic acid,and the daily average mass concentrations were 0.24?g·m^-3and 0.31?g·m^-3,respectively.?3?WSOA included C_xH_y⁺?32.1%?,C_xH_yO⁺?30.4%?,C_xH_yO₂⁺?25.4%?,and H_yO⁺?4.7%?identified by SP-AMS.The average oxygen-to-carbon?O/C?,hydrogen-to-carbon?H/C?,nitrogen-to-carbon?N/C?and organic matter-to-organic carbon?OM/OC?ratios of the WSOA were 0.72,1.53,0.04,and 2.15,respectively.Higher O/C indicated the higher contributions from secondary photochemical reaction conversion in Spring.Positive Matrix Factorization?PMF?analysis for AMS mass spectra of WSOA identified three sources,i.e.,hydrocarbon-like?HOA?,semi-volatile oxygenated OA?SVOOA?-biomass burning OA?BBOA?,and low-volatility oxygenated OA?LVOOA?,which on average accounted for18.4%,34.1%,and 47.4%of the total WSOA,respectively.SOA showed great contribution to WSOA during the observation period.?4?The total mass concentration of n-alkanes was 252.37 ng·m^-3during sampling period.Among them,medium and high molecular weight n-alkanes?C21-C33?accounted for up to79.7%.Correlation analysis with meteorological parameters showed that the total concentration of n-alkanes was positively correlated with atmospheric pressure.Diagnostic parameters calculated that n-alkanes were affected by both higher plant emissions and anthropogenic sources.Principal component analysis showed that n-alkanes was mainly affected by biological sources,automobile exhaust,coal burning and marine sources.The backward trajectory analysis?HYSPLIT 4.9 model?indicated that the total concentration of n-alkanes in the cluster 1 was the highest.However,there was no significant difference in the proportion of high molecular weight n-alkanes and low molecular weight n-alkanes among different transport paths.High molecular weight n-alkanes accounted for a high proportion?>75%?,indicating a strong contribution from biological sources.?5?The backward trajectory analysis of PM_2.5 indicated that cluster 4 accounted for nearly half?46%?and belonged to short-distance transmission.Cluster 1 accounted for 21%of the total trajectory,cluster 2 accounted for 13%,and cluster 3 accounted for 20%,respectively.These three clusters represented long-distance transmission,indicating that fine particles were affected by both local and long-distance sources.Finally,source apportionment results on all components derived from PMF model indicated that the major contributors of PM_2.5 were coal combustion?16.2%?,secondary aerosol formation?34.5%?,dust contribution?30.5%?,biomass burning?7.0%?and ocean emission?11.8%?.