| In recent years,the air quality of Changchun city decreased year by year.Frequent haze events have a negative impact on human health and life and its research has attracted lots of attention.At present,the fine particulate matter(PM2.5)has become the primary pollutant in the urban atmosphere in our country.Organic carbon?OC?and element carbon?EC?are the main components of them,and they have also received extensive attention.In order to understand the rule of OC and EC changing with time in Changchun,PM2.5 samples were collected by KC-120H particulate sampler during April 2017 to December 2017.OCEC analysis was carried out by NIOSH 5040 method to determine the concentration of OC and EC in PM2.5 in Changchun city.The results show that the average concentration of PM2.5 was 45.92?g/m3.The concentration of OC changed from 15.69-24.32?g/m3 and the concentration of EC changed from 1.38-2.33?g/m3.The mean concentrations of OC and EC were 21.70?g/m3 and 1.85?g/m3 respectively.In terms of the annual average,the concentration of OC and EC were lower at 5 a.m.and 3 p.m.;the concentration of OC peaked at 10 a.m.and 9 p.m.During the heating period,the average OC concentration was 24.68?g/m3,and the average EC concentration was 2.04?g/m3.During the non-heating period,the average OC concentration was 21.39?g/m3,and the average EC concentration was 1.44?g/m3.The average concentration of OC in PM2.5 in four seasons were 20.62?21.50?23.85?24.03?g/m3.The average concentration of EC in PM2.5 in four seasons were1.26?1.35?1.85?2.45?g/m3.The highest OC concentration appeared in November,with the value of 24.04?g/m3.The lowest OC concentration appeared in May,with the value of 18.44?g/m3.The highest EC concentration appeared in October,with the value of 2.37?g/m3.The lowest EC concentration appeared in August,with the value of 0.81?g/m3.Based on previous research results,combined with the 2017 Changchun PM2.5CMB model analytical results and related literature data,we obtained the contribution of different pollution sources to EC and OC in PM2.5 of Changchun city.OC came from motor vehicle exhaust,secondary particles,biomass burning,urban dust,coal dust,soil wind dust and construction dust,accounting for 25.26%,20.03%,18.57%,18.11%,14.23%,3.15%and 0.65%respectively.EC mainly came from the motor vehicle exhaust gas and coal dust,accounting for 46.25%and 39.15%,respectively.Other sources included the dust,biomass burning,building dust,soil wind dust,accounting for 6.54%,5.62%,1.60%,and 0.84%.In addition,the daily variation curve of annual OC and EC concentration in Changchun's atmosphere was fitted with the daily variation map of various sources'contribution to carbon components,showing a significant correlation.The annual OC/EC ratio ranged from 8.08 to 15.44,with an average value of 11.70,indicating that the main sources of OC and EC in Changchun are coal burning and ground dust,and there were organic carbon produced by secondary reaction.The main sources of OC and EC in heating period were coal burning and ground dust.The main sources of EC and OC in non-heating period were coal burning,ground dust and biomass burning.The main sources of EC and OC in spring,summer and autumn were coal burning,ground dust blowing and biomass burning;the main sources of EC and OC in winter were vehicle exhaust and coal burning.The peak of OC/EC mass concentration ratio were in the afternoon,because the temperature was high in the afternoon and the light was strong,which was conducive to the generation of secondary organic carbon?SOC?.The average concentration of OC in Changchun city was 21.7?g/m3,accounting for 52%of PM2.5 concentration.The average mass concentration of EC in Changchun city was 1.85?g/m3,accounting for 4.48%of PM2.5 concentration.The absolute concentration of OC and EC in heating period was higher than that in non-heating period,but the proportion of OC and EC in PM2.5 in heating period was smaller than that in non-heating period.This was due to the influence of PM2.5 concentrations.The absolute concentrations of OC and EC in four seasons were showing as winter>autumn>summer>spring,but the proportions of OC and EC in PM2.5 were showing as summer>spring>autumn>winter,which was due to the influence of PM2.5concentrations in different seasons.The annual correlation coefficient of OC and EC concentration was-0.19,indicating that the sources of OC and EC in PM2.5 of Changchun city were not consistent.October 20th,2017 was selected as the representative of heavy pollution weather in Changchun city,and the correlation between OC and EC and other air pollutants in PM2.5 were analyzed.The correlation coefficient between EC and PM2.5was 0.9,and they were correlated at the significance level?=0.001,which indicated that the main source of EC on that day wa very similar to the main source of PM2.5.The correlation coefficient between EC and NOX was 0.75,and they were correlated with significance level?=0.001.As NOX was mainly affected by automobile exhaust,so one of the main sources of EC on that day was vehicle exhaust. |
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