| Atmospheric fine particulate matter can have a significant impact on air quality,visibility,climate change and human health.In order to have an in-depth understanding of the physical and chemical characteristics of atmospheric fine particles in Chengdu,a typical city in Sichuan Basin,and explore the formation mechanism,source and evolution characteristics of fine particle pollution and other important information,an observation station was set up in the center of Chengdu,single particle aerosol mass spectrometer（SPAMS）was used to observe the single particle aerosol with high time resolution.Firstly,a comprehensive analysis of the seasonal characteristics of single-particle aerosols was achieved by analyzing the observation results in July 2020,October 2020,January 2021,and April to May 2021.Secondly,from January 15 to February 14,2020,targeted observations were made on single particle aerosols in the atmosphere of Chengdu city before and after the COVID-19 lockdown,and comparative analysis was made on the physical and chemical characteristics and pollution formation mechanism of single particles before and after the lockdown period.The annual average concentration of fine particulate matter(PM2.5)in Chengdu was 46.8±35.5μg/m3,which was 1.3 times of the second-level annual limit（35μg/m3）of the National Ambient Air Quality Standard（GB3095-2012）.The average mass concentration of PM2.5 in spring,summer,autumn and winter were 39.1±23.3μg/m3,22.4±18.1μg/m3,65.7±25.7μg/m3 and 45.1±34.3μg/m3,respectively.The PM2.5 in autumn and winter were significantly higher than spring and summer.The average concentration of sulfur dioxide（SO2）was 5.6±9.8μg/m3.The seasonal variation of SO2was higher in spring（7.9±17.6μg/m3）and lower in winter（4.6±2.8μg/m3）.The average concentrations of nitric oxide（NO）and nitrogen dioxide（NO2）were 15.1±29.4μg/m3 and 56.5±30.2μg/m3,respectively.NO and NO2 were higher in winter（27.4±39.5μg/m3 and 80.8±23.1μg/m3）and lower in summer（4.6±2.8μg/m3and 32.4±17.8μg/m3）.The average concentration of carbon monoxide（CO）was 0.8±1.2mg/m3,appeared a seasonal change of high（1.0±0.9 mg/m3）in winter and low（0.5±0.5mg/m3）in autumn.Under the influence of the seasonal difference of photochemical reaction intensity,the average concentration of O3 was higher in summer（69.8±50.7μg/m3）and lower in winter（25.2±26.8μg/m3）.Atmospheric particulate matter in Chengdu were clustered into eight categories:biomass burning（BB）,coal combustion（CC）,vehicle emissions（VE）,cooking emissions（CE）,Dust（DUST）,and three kinds of secondary inorganic particles,K-nitrate（K-NO3）,K-sulfate（K-SO4）and K-sulfate-nitrate（KSN）.VE had always been the type of particulate matter with the highest contribution in the four seasons,and its contribution range was 25.5%～29.1%.Among the three typical secondary inorganic particles,K-SO4 was higher than K-NO3and KSN particles in spring,summer and autumn.Under the influence of low temperature and high humidity in winter,the contribution of K-NO3 particles became the second largest particle type after VE,reaching 18.7%.Under the influence of biomass burning activities in Sichuan Basin,BB particles showed relatively stable contribution in all seasons（12.9%～16.0%）.In contrast,other types of particles（CC,DUST and CE particles）contribute less,but they also showed their own unique seasonal characteristics due to the influence of their emission sources and generation mechanism.In spring,the air mass mainly came from the east and west of Chengdu.The air mass from the west corresponded to the higher PM2.5 concentration,and VE and BB particles had higher contribution.In summer,the air mass mainly came from the east of Chengdu,and the corresponding PM2.5concentration was relatively low.In autumn,the air mass mainly came from the east of Chengdu.The air mass from the northeast and southeast corresponded to the higher PM2.5 concentration,and the particulate matter contribution was higher for VE and BB particles.In winter,the air mass mainly came from the east and west.The air mass originating from the northwest corresponded to the higher PM2.5 concentration,and the higher contribution of particulate matter were VE and K-NO3 particles.Observations before and after the COVID-19 lockdown,showed that PM2.5,NO,NO2,SO2 and CO concentrations decreased by 38.6%,77.5%,47.0%,35.1%and 14.1%after the COVID-19 lockdown,while O3 concentration increased by 57.5%.Compared to before the COVID-19 lockdown,the contribution of VE particles experienced the greatest decline（by 14.9%）,whereas the contributions of BB and CE particles increased by 7.0%and 7.3%,respectively,after the COVID-19 lockdown.Regional transmission was critical for pollution formation before the COVID-19 lockdown,whereas the pollution that occurred during the lockdown period was caused mainly by locally emitted particles（such as VE,CE and BB particles）.Weighted potential source contribution function（WPSCF）analysis further verified and emphasized the difference in the contribution of regional transmission for pollution formation before and during lockdown.In addition,the potential source area and intensity of the particles emitted from different sources or formation mechanisms were quite different. |
PDF Full Text Request