| The process of atmospheric pollution represented by haze can cause serious harm to human health.And haze is mainly caused by submicron aerosols(PM1,aerodynamic diameter of less than 1 ?m),however,a large number of studies have focused on PM10 and PM2.5,which requires more sophisticated instruments to analyze small particle size components during the haze process.In this paper,using the aerosol chemical species monitor(ACSM)and other advanced instruments,mass concentrations,chemical species and size distributions of submicron aerosol were observed and analyzed in Beijing(regions influenced by human cooking and traffic activities)and Xingtai(regions influenced by heavy industry).Based on the long-term real-time submicron aerosol observations at two observation site,the temporal variation,source characteristics and forming mechanism of submicron aerosol chemical composition in different source emission scenarios were studied,the effects of regional emission control and local emission reduction on air pollution were revealed,the impacts of the winter coal combustion,the Spring Festival holiday,the emission of fireworks and APEC control measures on PM1 were quantitatively assessed and the relationship between new particle growth and PM1 chemical species was discussed.By comparing with the corresponding studies of PM10 and PM2.5,we try to find out more new features,phenomena and changes of PM1,which are different from PM10 and PM2.5.These studies provide scientific basis for the formation mechanism and control measures of haze in different source emission scenarios,and also provide scientific data and theoretical basis for numerical simulation of submicron aerosols.Through the continuous and enhanced observation of submicron aerosols in Beijing and Xingtai between 2011 and 2016,the effects of four seasons,winter coal,Chinese Spring Festival,fireworks emission and APEC control on submicron aerosols were studies.Some meaningful results were obtained.1.The diurnal variation,monthly variation and seasonal variation of submicron aerosols in BeijingThe chemical composition of submicron aerosols is mainly composed of organie matter,sulfate,nitrate,ammonium and chloride.The diurnal variations of organic matter and nitrate are characterized by bimodal type,peaking at noon and evening,similar to diurnal variations of PM2.5,but the peak of organics is more high;chloride,sulfate and ammonium showed a single peak distribution,troughs of sulfate and ammonium appeared in 8 o'clock,while that of chloride appeared in 15 o'clock,the diurnal variation is similar to SO2 and NOx in previous studies.The monthly variations of all chemical species are characterized by bimodal peaks and the high values appeared in June and December,with the most obvious change in chloride and the relative small changes in the other components.The seasonal variation characteristics of the contribution to PM1 of organics and chloride are winter>autumn>spring>summer,that of sulfate and ammonium are summer>spring>winter>autumn,and that of nitrate is summer>spring>autumn>winter.At the same time,compared with the previous studies on PM2.5 and PM10,it was found that 1)mass concentrations of PM1 was not significantly different between four seasons,which was the lowest in the spring and autumn and the highest in summer,followed by winter and it is different from the conclusion which the highest concentration of PM10 appeared in spring in Beijing.2)Excluding coal and biomass burning,the diurnal variation of chloride is almost dependent on the change of the boundary layer height,that is,the coal combustion and biomass burning increased the chloride.The increase of chloride concentration can be used as an important indicator of coal combustion and biomass burning.2.The impact of heating period,Chinese Spring Festival holiday and fireworks on submicron aerosolsOrganics can be divided into three types,mineral combustion(FOA),cooking emission(COA)and secondary formation(OOA)using positive matrix factorization and decomposition(PMF).Compared with non-heating periods,the PM1 concentration increased by 45%in the heating periods,and the FOA,COA,OOA and various inorganic species increased.Among them,FOA and chloride increased the most significantly,which increased 4.8 times and 1.2times,respectively.Compared with the heating period for removing the holidays,in addition to the increase in sulfate,the OOA and ammonium remained unchanged and the remaining organic matter and inorganic species decreased,with PM1,COA and FOA concentration falling by 42%,68%and 71%,due to the large reduction in human activities during holiday.During fireworks emission periods,PM1 concentration did not change drastically and PM2.5 concentration increased dramatically,PM1/PM2.5 is only 40%,indicating that fireworks emission mainly produces PM1-2.5 and has little effect on PM1 mass concentration.At the same time,contribution to PM1 of FOA and chloride increased,while that of OOA,nitrate and ammonium are almost unchanged.The previous studies of PM10 and PM2.5 indicate a significant increase in organic matter and sulfate during the heating periods.This study further points out that the increase of organic matter in the heating periods is the same,and the increase of chloride is mainly from PM1,while the increase of sulfate in PM1 is small and the contribution reduced,suggesting that sulfate is mainly from PM 1-2.5.3.The impact of APEC control measures on submicron aerosolsDue to the implementation of regional emission control measures,mass concentration of PM1,organic and inorganic matter decreased significantly,by 63%,62%and 64%,respectively.However,the aerosol contribution changed little before and during APEC control,such as the contribution of organic matter,nitrate and sulfate changed 1%,2%and-4%,respectively.At the same time,compared with the previous studies of PM10 and PM2.5,it was found that PM10,PM2.5 and PM1 decreased by 67%,65%and 63%,respectively during the regional source emission control periods,indicating that the effect of regional emission control on decreasing PM concentration is significant,in a certain range,the larger the particle size is,the more significant the effect is.The contribution to PM2.5 of secondary inorganic species during APEC control periods decreased by 51%,but the contribution to PMI almost changed little,indicating that regional source emission control has a significant impact on secondary inorganic species from regional transport,while has little impact on local secondary formation.4.Gas particle transformation and new particle growth.The concentrations of SO2,NOv,sulfate and nitrate were observed simultaneously by thermoelectric instrument and ACSM every 15 minutes.At the same time,using the gas particle conversion indicator such as sulfur oxidation rate(SOR)and nitrogen oxidation rate(NOR),approximately 30000 samples were studies for gas particle transformation.The results show that the correlation between NOR and SOR is 0.79,and the reliability test of 0.001 was completed,indicating that the two kinds of gas particle conversion have good consistency.The diurnal variations of NOR and SOR are both bimodal,and the peak of NOR appears at about 15 and 3 o'clock,which is related to the diurnal variation of temperature.And the peak of SOR appears at 20 and 1 o'elock,which may be related to temperature and relative humidity.NOR fluctuated between 0-0.55,the highest is in June(17%)and the lowest is in November(3%).SOR fluctuates between 0-72%and its trend is similar to that of NOR,the highest is in June(32%)and the lowest is in February(4%),indicating SOR is stronger than NOR.NOR and SOR have a significant positive correlation with meteorological parameters(relative humidity and temperature),passing the reliability test of 0.001,but when relative humidity is 80%and the temperature is 30?,the ability of gas particle conversion begins to decrease with their rise.However,the SOR increases with relative humidity,resulting from the enhanced liquid phase reaction with high relative humidity promotes the conversion of SO2 to sulfate.SMPS can detect the particle number size distribution,which can reflect new particle growth events.In the heavily polluted Xingtai,new particle growth events are frequent,about 58%of the observation time,indicating that the new particle growth events not only appear in the clean days,but also in the polluted days.The diurnal variations of the contribution to PM1 of sulfate and OOA is the same as that of particle growth,suggesting that sulfate and OOA play an important role in the new particle growth events.Compared with polluted days,new particle growth events are the same during daytime,and the more obvious during nighttime in clean days,possibly due to the increase in OOA over the night in clean days.Compared with the previous studies,it was found that secondary organic aerosols played an important role in the growth of particles,and primary organic aerosols were not so useful.OOA is more important than sulfate in new particle growth events. |
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