| In recent years,fine particles pollution has become a serious issue in Beijing,the political,economical and cultural center of China.With the rapid economic development,accelerating industrialization and urbanization process,the energy consumption and vehicle population continues to surge of Beijing and its surrounding areas,leading to air quality continues to deteriorate,high fine particles(PM2.5)concentrations and heavy regional haze pollution incidents occur frequently.Submicron particles(PM1),is an important component of PM2.5,which exhibit the properties of lengthy atmospheric residence time,large specific surface area and high light scattering efficiency,have been found to play a key role in global climate change and in human health.Therefore,understanding the characteristics of submicron particles has fundamental meaning to study their behavior and effects.In this study,we performed a highly time-resolved chemical characterization of submicron particles at the Institute of Atmospheric Physics(IAP),Chinese Academy of Sciences(116.37 o E,39.97 o N)in Beijing from 2015.08 to 2016.08,using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer(HR-ToF-AMS),Amulti-angle absorption photometer(MAAP;model 5012,Thermo Electron Cooperation)and a Rapid Collector of Fine Particles and Ion Chromatogra-physystem(RCFP-IC).After processed and analyzed the observational data,we discussed(1)the characteristics of mass concentration,chemical composition,diurnal variation and the aerosol acidity;(2)To study the impact of long-distance transmission on the air pollution of Beijing based on the HYSPLIT 4.9 air mass trajectory model;(3)in order to evaluate the effects of the implementation of emission reduction measures and the revolution of air quality during the 70 th anniversary of victory parade in Beijing;(4)to study the effect of firecracker setting-off on the fine particle pollution in city during the Spring Festival in 2015,based on the data of the mass concentration and the component of water-souble ions of PM1 and PM2.5 by using RCFP-IC instruments;(5)to analysed the seasonal elemental ratios composition and polycyclic aromatic hydrocarbons(PAHs)of OA in submicron particles;(6)we used the positive matrix factorization(PMF)model to merge the high-resolution mass spectra of the organics and nitrate,and identified components of organic aerosol(OA)and nitrate inorganic aerosol(NIA),in addition,we calculated the mass concentrations of the inorganic nitrate and organic nitrate from the mass spectra of one NIA factor and OA factors,respectively.The main findings are as follows:(1)During this study,the seasonal average mass concentrations of PM1 in Beijing were 44.1±49.5,31.8±21.1,46.4±58.0 and 61.7±71.6 ?g?m-3 in spring,summer,autumn and winter.These results indicating that the air quality in winter was the worst,and in summer was best;the air quality in in spring and autumn was better than winter.Organics dominated PM1 during all seasons,accounting for 40%,41%,50% and 52% in spring,summer,autumn and winter.About the inorganic components,the sulfate,nitrate and ammonium accounted for 20%,17% and 13% of PM1 in summer,respectively;the contribution of nitrate in spring and summer was slightly higher than sulfate;the contribution of sulfate in summer and winter was higher than nitrate.Bacause of the coal conbustion activities were frequently occurred in winter in Beijing and surrounding areas,the sulfate accounted for 18% of PM1;due to a significant increase of photochemical reaction in summer,precursor SO2 can be oxidized to form sulfate via either gas-phase oxidation or aqueous-phase processing,leading to the sulfate accounted for 20% of PM1.The nitrate and sulfate accounted for 16% and 15% of PM1 in autumn,respectively;The contribution of ammonium range from 7% to 13%,and the highest value was all appear in spring and summer,the lowest value were appear in winter;the contribution of BC was relatively stable and range from 8% to 11%.The highest contribution of chloride was appear in spring and winter,which closely related to dust storm and the coal combustion in Beijing.(2)The diurnal variation of each component also showed some difference in four seasons.The organics peaks appeared in the morning(8:00-9:00)and in the evening(19:00-22:00),the peak values were 16.7 and 22.5,12.7 and 14.1,20.1 and 30.5,25.6 and 37.5 ?g?m-3,the evening peaks in four seasons all were apparently higher than noon peaks.Because of heavy and light diesel vehicles could be allowed to thread at night in Beijing urban areas,the diurnal concentration at night was higher than the daytime.The nitrate appeared peak values at noon(11:00-12:00)in spring,summer and autumn,the nitrate was slightly increase in winter from 10:00 am.The sulfate appeared peak values in the afternoon at 15:00 in four seasons.(3)On the polluted days,the contribution of organics appeared decreasing,and the inorganics secondary species,including sulfate,nitrate and ammonium,increased rapidly,especially on the heavy pollution days.The OOA(LV-OOA+SV-OOA)dominated OA during all seasons;the contribution of BBOA and CCOA was stable on different pollution condition;the COA and HOA appeared apparently cifference in different pollution condition in all seasons.(4)The chloride,nitrate,sulfate and ammonium appeared consisitent varied trend in all seasons by using AMS and RCFP-IC instruments.The chloride mass concentration measured by AMS in spring was lower than RCFP-IC;the nitrate and sulfate measured by AMS in summer and winter were higher than RCFP-IC;the ammonium measured by AMS in all seasons was lower than RCFP-IC.(5)The acidity of the submicron aerosol was estimated by comparing measured NH4+ mass concentration(NH4+ measured)to the amount needed to fully neutralize the measured SO42-,NO3-and Cl-(NH4+ predicted),indicating that the submicron aerosol appeared acidity in all seasons,but the intensity of submicron aerosol acidity in winter was higher than other seasons.(6)The effects of long-distance transmission on the air pollution in Beijing were very different in four seasons after the clustering analysis.The air masses directions were diversity in spring and winter,while mainly from northwest and southwest of Beijing in summer and autumn.The air masses from south carried high mass concentration of submicron particles and dominated by the inorganic species and organics,while the mass concentration of submicron aerosol in the air masses from north was significantly lower than that in south and mainly composed organics.(7)The mass cocentration of PM2.5 and PM1 were 13.5 and 12.0 ?g?m-3during the 70 th anniversary of victory parade periods in Beijing(2015.8.20-2015.9.3),organics contributed to PM1 more than 60%,the concentration of PM2.5 and PM1 decreased 74.7% and 72.2% with comparing the before the parade periods(2015.8.12-2015.8.19).The mass concentration of PM2.5 and PM1 in creased with cancel of the pollution control measures after the parade periods(2015.9.4-2015.9.10)and reaching to 27 and 31 ?g?m3,the contribution of sulfate and nitrate inhanced apparently.(8)The average mass concentration of PM10,PM2.5 and PM1 were 589,414 and 318 ?g?m-3 during firecracker setting-off of Spring Festival in 2015(2016.2.7 20:00-2016.2.8 8:00),the ratios of PM2.5/PM10 was 0.70,indicating that the fine particles dominated of pollutants.The total water-souble ions(TWSI)mass concentration of PM2.5 and PM1 were 277 and 146 ?g?m-3,accounting for 46.0% and 66.8% of PM2.5 and PM1 mass concentration,respectively.The average mass concentrations of K+,Cl-and SO42-of PM2.5were 101,51 and 101 ?g?m-3,accounting for 36%,18% and 38% of TWSI mass concentration;The average mass concentrations of K+,Cl-and SO42-of PM1 were 39,34 and 55 ?g?m-3,accounting for 25%,22% and 38% of TWSI mass concentration.(9)Using PMF model analysis for high resolution mass spectra(HRMS)merged of OA and nitrate indicating that five same factors can be identified in all seasons,including low-volatile OA(LV-OOA),semi-volatile OA(SV-OOA),cooking OA(COA),hydrocarbon-like OA(HOA)and nitrate inorganic aerosol(NIA).In addition,due to effect of biomass burning and coal combustion,the biomass burning OA and coal combustion OA can be seperated from OA in the autumn and winter,respectively.The LV-OOA,SV-OOA,COA and HOA accounted for 29%,34%,17% and 20% of OA in spring;accounted for 47%,12%,22% and 19% of OA in summer;accounted for 43%,12%,18% and11% of OA in autumn;accounted for 16%,22%,13% and 25% of OA in winter.The BBOA and CCOA accounted for 16% and 24% of OA in autumn and winter,respectively.(10)Through HRMS of HR-ToF-AMS analysis,the polycyclic aromatic hydrocarbons(PAHs)of submicron organic aerosol can be calculated in different seasons,the results indicated that the mass concentration of PAHs was lowest in summer(0.01±0.004 ?g?m-3),and highest in winter(0.22±0.24 ?g?m-3),the mass concentrations of PAHs in spring and autumn were 0.03±0.03 and 0.04±0.01 ?g?m-3,respectively.The diurnal mass concentration of PAHs in winter was prominently higher than other seasons and the concentration at night was higher than the daytime.(11)Through the contribution of mass fraction of NOx ions(NO+ and NO2+)in NIA and components of OA and combine to the methods of calculation,the mass concentration of inorganic nitrate and organic nitrate can be quantified in four seasons.The results indicating that the organic nitrate mass concentration in all seasons appeared the winter(2.5±2.3 ?g?m-3)>the autumn(0.8±1.2 ?g?m-3)> the summer(0.5±0.2 ?g?m-3)>the spring(0.6±0.5 ?g?m-3);the inorganic nitrate mass concentration was winter(7.6±8.2 ?g?m-3)>the autumn(6.8±11.0 ?g?m-3)> the summer(6.1±5.8 ?g?m-3)>spring(4.1±5.7 ?g?m-3).The diurnal mass cocentration of organic mass concentration in daytime in summer was higher than the night time,but appeared oppersite trend in other seaons.The diurnal variation of inorganic nitrate appeared difference in different seasons. |
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