| 北京城区不同组分PM2.5散射特性及来源分析 |
| 摘要点击 2535 全文点击 2670 投稿时间：2022-04-14 修订日期：2022-05-25 |
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| 中文关键词 北京城区 PM2.5组分 散射系数 IMPROVE重构 日变化 潜在源区 |
| 英文关键词 Beijing urban area PM2.5 components scattering coefficient IMPROVE reconstruction diurnal variation potential source regions |
| 作者 | 单位 | E-mail | | 曹阳 | 北京市生态环境监测中心, 大气颗粒物监测技术北京市重点实验室, 北京 100048 | caoyang1990x@126.com | | 王陈婧 | 北京市生态环境监测中心, 大气颗粒物监测技术北京市重点实验室, 北京 100048 | | | 景宽 | 北京市生态环境监测中心, 大气颗粒物监测技术北京市重点实验室, 北京 100048 | | | 王琴 | 北京市生态环境监测中心, 大气颗粒物监测技术北京市重点实验室, 北京 100048 | | | 刘保献 | 北京市生态环境监测中心, 大气颗粒物监测技术北京市重点实验室, 北京 100048 | | | 安欣欣 | 北京市生态环境监测中心, 大气颗粒物监测技术北京市重点实验室, 北京 100048 | anxinxin2002@163.com |
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| 中文摘要 |
| 近年来北京城区PM2.5浓度下降伴随其中二次离子占比升高，为探索不同组分PM2.5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PM2.5及其组分浓度和散射系数的连续在线监测，分析了PM2.5组分及散射的特征和来源.结果表明，研究期间北京城区PM2.5最主要组分为NO3-，PM2.5中ω（NO3-）和ω（SNA）分别为24%和46%.根据浓度和组分占比将PM2.5划分为6种类型：优型出现频率最高，为56%，四季分布均匀，PM2.5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，PM2.5中ω（FS）和ω（OM）分别为66%和46%，主要分布于春季和夏季；OM+SO42-（OS）型多分布于夏季午后，OM+NO3-（ON）型多分布于冬季凌晨和上午，NO3-（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PM2.5的MSE最高，为4.3m2 ·g-1，D型最低，为2.1m2 ·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PM2.5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Bsca为203.8 Mm-1，N型PM2.5贡献率最大，为53%，大颗粒NH4NO3为主要贡献物质，优型PM2.5的Bsca为67.2 Mm-1，小颗粒OM为主要贡献物质，与全年Bsca（dry）相比，Bsca放大了1.5倍，其中SNA贡献放大了1.8~2.1倍.NO3-和相对湿度同时在07：00前后出现最高峰值，导致NH4NO3在该时刻Bsca达到最大，SO42-峰值主要出现在16：00，（NH4）2SO4的Bsca峰值出现在04：00，OM浓度和其Bsca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NO3-、SO42-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Bsca潜在源权重贡献因子在该区域的数值增大. |
| 英文摘要 |
| In recent years, the concentration of PM2.5 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 PM2.5 with different chemical compositions, PM2.5 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 PM2.5 were analyzed. The results showed that NO3- was the major component of PM2.5 in the Beijing urban area, and the ω(NO3-) and ω(SNA) were 24% and 46% in PM2.5, respectively. PM2.5 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 PM2.5, 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 PM2.5, respectively. The OM+SO42-(OS)-type, OM+NO3-(ON)-type, and NO3-(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)<40%], the MSE of N-type PM2.5 was the highest (4.3 m2·g-1), and that of D-type PM2.5 was the lowest (2.1 m2·g-1), reflecting the high scattering ability of SNA. The MSE increased with relative humidity. Under the condition of high humidity (RH>80%), the MSE of all types of PM2.5 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 Bsca was 203.8 Mm-1, and N-type PM2.5 contributed the most, accounting for 53%, in which the large particles of NH4NO3 were the major contributor. Bsca of good-type PM2.5 was 67.2 Mm-1, in which small particles of OM were the major contributor. Bsca was 1.5 times the annual Bsca(dry), whereas the Bsca values of SNA were 1.8 to 2.1 times the Bsca(dry). The peak value of NO3- and RH simultaneously appeared around 07:00, resulting in the maximum Bsca of NH4NO3 at this time. The peak value of SO42- and the Bsca of (NH4)2SO4 mainly appeared at 16:00 and at 04:00, respectively. The diurnal variation curves of OM concentration and Bsca were consistent, and the bimodal peaks appeared at 13:00 and 20:00, respectively. In spring and winter, NO3-, SO42- 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 Bsca of SNA in this region. |
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