| The Beijing metropolitan region is one of three leading economic centers of China.And this region is suffering from serious pollution due to rapid development of industry and urbanization.Hence,it is important to monitor the pollution,definite the the source and component and put forward measures.In this paper,we use various kinds of observation data to analyze the aerosol concentration,chemical component,optical property and the relationship between them.We revealed the spatial and temporal characteristic,main source and light extinction distribution of aerosol,and we clarified the impacts of aerosol concentration,chemical component on optical property and provided suggestions for controlling pollution and improving visibility over the Beijing region.The main results are as fellows.The annual means of PM2.5(PM10)were 62±45(130±88)?g·m-3and 79±61(142±96)?g·m-3 in the city and suburban region,which were much higher than the regional background(PM2.5: 36±29?g·m-3).PM concentration in Beijing and Xianghe far exceeded the China environment standard(PM2.5: 35?g·m-3,PM10: 75?g·m-3).The annual means of AOD were 0.53±0.47 and 0.54±0.46 and 0.24±0.22 in the city,suburban and the background region,respectively.The annual means of ?ngstr?m exponents were 1.11±0.31 and 1.09±0.31 and 1.02±0.31 in three typical stations,the main fraction in this region is fine particles.When this region is dominated by the air mass of Type-V,pollution here was serious.The AOD reached 1.08,PM2.5,PM10 concentration reached 78?g·m-3 and 152?g·m-3 at Beijing station.The meteorological factors work together to exert an influence on aerosol concentrations.Meteorological factors work together to exert an influence on aerosol concentrations.When RH is higher than 60%,the wind speed is less than 2m/s,and MLH is lower than 200 m,PM2.5 concentration reached the maximum.From 2005 to 2014,the PM2.5(PM10)concentration decreased by 6(3)?g·m-3.Except winter,the three other seasons showed a small decline in PM concentration.The particle pollution was serious over the Beijing metropolitan region.The small decline of Angstrom exponent reflected the increasing of coarse aerosols' rate.We analyzed the aerosol components of NR-PM1 during different seasons and air masses.In the overall condition,the organics accounted for the most in the NR-PM1(56%),and the concentration of organics was 26?g·m-3.In summer,the sulfate accounted for a higher percentage than other seasons(26%),the concentration of sulfate in summer was 10?g·m-3.In autumn,nitrate accounted a higher percentage than other seasons(19%),the concentration of nitrate was 11?g·m-3 in autumn.The mean ratio of sulfate and nitrate were all larger than 1 during different seasons and air masses.It showed that stationary source is the main source of Beijing region.But in serious polluted days,the contribution of moving source increased.It's of vital importance for knowing the diatribution of atmospheric pollution using the satellite data.The linear regression functions of PM2.5(y)and ground-observed AOD(x)were with high correlation coefficient in the three typical areas,which were y=74x+18(R2=0.58,N=337,in the City),y=80x+25(R2=0.55,N=306,in the suburban)and y=87x+9(R2=0.64,N=350,in the background).The functions of PM10(y)and ground-observed AOD(x)were y=112x+57(R2=0.54,N=337,in the city)and y=114x+68(R2=0.47,N=304,in the suburban).But the functions had large differences in four seasons.The slopes of functions ranged from 55 to 101,and intercept ranged from 2 to 24 in four seasons at Beijing station.With MODIS C6 AOD,the distributions of PM2.5 and PM10 concentration were retrieved by the seasonal functions.In sunny days,PM2.5 concentration was less than 40?g·m-3 in the northwest part of this region and more than 60?g·m-3 in the southeast region;PM10 concentration was less than 80?g·m-3 in the northwest part of this region and more than 120?g·m-3 in the southeast region The absolute retrieval errors of seasonal PM2.5 distribution were less than 5?g·m-3 in the pollutant city and suburban,and less than 7?g·m-3 in the clean background.There were thresholds of PM2.5 concentration for aerosol extinction by using the long-term observation data.When the PM concentration was lower than a certain threshold,AOD decreased quickly with the decline of PM concentration.To make people feel the improvement of particle pollution,the PM concentration should be controlled under the threshold.The annual averaged threshold is 63?g·m-3,and the threshold values reached the maximum of 74?g·m-3 in spring,ranged from 54 to 56?g·m-3 in the three other seasons.The threshold values ranged from 55 to 77?g·m-3 under other relevant factors,including air masses directions and relative humidity.This provided periodical target for pollution control.We used the component of NR-PM1 observed by an AMS and the ISORPOPIA model to calculate the concentration of compound.And we calculated the aerosol extinction coefficient by using AOD and MLH.Furthermore,we obtained the regression functions between the extinction coefficient and compound concentration,and calculated the contribution for light extinction of each kind of compound.Under the overall condition,organics,ammonium chloride,ammonium nitrate,ammonium sulfate,black carbon contributed 30%,6%,24%,26% and 6% of the total light extinction,respectively;In spring and summer,ammonium sulfate contributed most,reaching 30% and 32%;In autumn,ammonium nitrate contributed the most,reaching 40%;ammonium nitrate contributed most in winter,reaching 9%.By comparing the light extinction contribution of different components dominated by different air masses,the organics and ammonium sulfate contributed more under severe polluted days.These results provided scientific basis for controlling air pollution and improving visibility effectively. |
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