摘要
近年来北京城区PM_(2.5)浓度下降伴随其中二次离子占比升高,为探索不同组分PM_(2.5)散射特性及其来源,于2020年12月至2021年11月开展了小时分辨率的PM_(2.5)及其组分浓度和散射系数的连续在线监测,分析了PM_(2.5)组分及散射的特征和来源.结果表明,研究期间北京城区PM_(2.5)最主要组分为NO^(-)_(3),PM_(2.5)中ω(NO^(-)_(3))和ω(SNA)分别为24%和46%.根据浓度和组分占比将PM_(2.5)划分为6种类型:优型出现频率最高,为56%,四季分布均匀,PM_(2.5)中ω(SNA)、ω(OM)和ω(FS)相当,分别为32%、 32%和28%;沙尘(D)型和OM(O)型全年出现频率较低,分别以FS和OM为主要组分,PM_(2.5)中ω(FS)和ω(OM)分别为66%和46%,主要分布于春季和夏季;OM+SO_(4)^(2-)(OS)型多分布于夏季午后,OM+NO^(-)_(3)(ON)型多分布于冬季凌晨和上午,NO^(-)_(3)(N)型多分布于春季及每日07:00前后.低湿(相对湿度<40%)条件,N型PM_(2.5)的MSE最高,为4.3m^(2)·g^(-1),D型最低,为2.1m^(2)·g^(-1),体现了二次盐类的高散射能力,MSE随相对湿度增加而增大,高湿(相对湿度>80%)条件,多类型PM_(2.5)的MSE升高为低湿的1.5~1.8倍,SAE结果显示颗粒物粒径随相对湿度增加有增大趋势.非高湿条件下,小时分辨率IMPROVE重构散射系数与实测值拟合较好,R介于0.81~0.97之间,除D型外,斜率介于1.00~1.21之间,N型拟合结果最好;高湿条件下R和斜率分别介于0.82~0.84和0.48~0.53之间.全年B_(sca)为203.8 Mm^(-1),N型PM_(2.5)贡献率最大,为53%,大颗粒NH_(4)NO_(3)为主要贡献物质,优型PM_(2.5)的B_(sca)为67.2 Mm^(-1),小颗粒OM为主要贡献物质,与全年B_(sca)(dry)相比,B_(sca)放大了1.5倍,其中SNA贡献放大了1.8~2.1倍.NO^(-)_(3)和相对湿度同时在07:00前后出现最高峰值,导致NH_(4)NO_(3)在该时刻B_(sca)达到最大,SO_(4)^(2-)峰值主要出现在16:00,(NH_(4))_(2)SO_(4)的B_(sca)峰值出现在04:00,OM浓度和其B_(sca)日变化曲线趋势较一致,双峰分别出现在13:00和20:00.春冬季NO^(-)_(3)、 SO_(4)^(2-)及OM主要来自太行山脉以东的平原区,夏秋季潜在源区较分散,FS主要潜在源区为春秋季西北向区域;途经华北平原南部、东南部和环渤海东部区域的高湿气流易导致SNA的B_(sca)潜在源权重贡献因子在该区域的数值增大.
In recent years,the concentration of PM_(2.5) in the Beijing urban area has decreased with the increase in the proportion of secondary inorganic ions.In order to explore the characteristics and sources of the light scattering of PM_(2.5) with different chemical compositions,PM_(2.5) with its chemical components and scattering coefficient were continuously measured at hourly resolution in the Beijing urban area from December 2020 to November 2021.The components,scattering characteristics,and sources of PM_(2.5) were analyzed.The results showed that NO^(-)_(3) was the major component of PM_(2.5) in the Beijing urban area,and the ω(NO^(-)_(3)) and ω(SNA) were 24% and 46% in PM_(2.5),respectively.PM_(2.5) could be divided into six types according to mass concentration and component proportion.The occurrence frequency of the good-type was the highest during the study with a similar duration in the four seasons,and the ω(SNA),ω(OM),and ω(FS) were 32%,32%,and 28% in PM_(2.5),respectively.The dust(D)-type and the OM(O)-type appeared mainly in spring and summer with the lowest frequency during the study.FS and OM were their major components,and the ω(FS) and ω(OM) were 66% and 46% in PM_(2.5),respectively.The OM+SO_(4)^(2-)(OS)-type,OM+NO^(-)_(3)(ON)-type,and NO^(-)_(3)(N)-type appeared mainly in the afternoon in summer,in the early morning and morning in winter,and at approximately 07:00 every day in spring.Under the condition of low humidity [relative humidity(RH)80%),the MSE of all types of PM_(2.5) rose to 1.5 to 1.8 times the values under low humidity.The variation trends of SAE showed that particle size increased with the rising of RH level.Under non-high humidity conditions,the scattering coefficients reconstructed by the revised IMPROVE formula fitted well with the measured values at hourly resolution,the correlation coefficients were between 0.81 and 0.97,and the slopes were between 1.00 and 1.21 except for that of D-type.The N-type fitting result was the best.Under high-humidity conditions,the R and the slopes were from 0.82 to 0.84 and from 0.48 to 0.53,respectively.The annual B_(sca) was 203.8 Mm^(-1),and N-type PM_(2.5) contributed the most,accounting for 53%,in which the large particles of NH_(4)NO_(3) were the major contributor.B_(sca) of good-type PM_(2.5) was 67.2 Mm^(-1),in which small particles of OM were the major contributor.B_(sca) was 1.5 times the annual B_(sca)(dry),whereas the B_(sca) values of SNA were 1.8 to 2.1 times the B_(sca)(dry).The peak value of NO^(-)_(3) and RH simultaneously appeared around 07:00,resulting in the maximum B_(sca) of NH_(4)NO_(3) at this time.The peak value of SO_(4)^(2-) and the B_(sca) of(NH_(4))_(2)SO_(4) mainly appeared at 16:00 and at 04:00,respectively.The diurnal variation curves of OM concentration and B_(sca) were consistent,and the bimodal peaks appeared at 13:00 and 20:00,respectively.In spring and winter,NO^(-)_(3),SO_(4)^(2-) and OM mainly came from the plains east of the Taihang Mountains,and their potential source regions were not in any particular place in summer and autumn;the main potential source regions of FS were the northwest areas of Beijing in spring and autumn.The flow with high RH across the south and southeast of the north China plain and the eastern rim of Bohai Sea was likely to increase the weighted potential source contribution factor values of B_(sca) of SNA in this region.
作者
曹阳
王陈婧
景宽
王琴
刘保献
安欣欣
CAO Yang;WANG Chen-jing;JING Kuan;WANG Qin;LIU Bao-xian;AN Xin-xin(Beijing Key Laboratory of Airborne Particulate Matter Monitoring Technology,Beijing Municipal Ecological and Environmental Monitoring Center,Beijing 100048,China)
出处
《环境科学》
EI
CAS
CSCD
北大核心
2023年第2期658-669,共12页
Environmental Science
关键词
北京城区
PM_(2.5)组分
散射系数
IMPROVE重构
日变化
潜在源区
Beijing urban area
PM_(2.5)components
scattering coefficient
IMPROVE reconstruction
diurnal variation
potential source regions
