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2021年中国生态环境状况公报显示,339个地级及以上城市平均超标天数 (空气质量指数大于100的天数为超标天数) 比例为12.5%,以PM2.5和PM10为首要污染物的超标天数分别占总超标天数的39.7%和25.2%。大气颗粒物已经成为影响我国城市空气质量的重要污染物[1-4]。道路扬尘对大气颗粒物的贡献可达到20%[5-7],已成为影响人群健康、环境污染、大气能见度的重要因素[8-10]。
碳组分是道路扬尘的重要组成成分,因其来源复杂日益受到广泛关注。目前,针对道路扬尘碳组分的研究主要集中于时空分布和来源解析[11-17]。马妍等[12]基于样方法研究了天津市春季道路扬尘中碳组分的特征,并进行了来源解析,发现天津市快速路中各碳组分质量分数均较高,次干道中各碳组分质量分数均较低。胡月琪等[13]研究了北京市典型道路扬尘化学组分的特征及年际变化,发现与2004年相比,2013年北京市道路扬尘PM2.5中除SO42-含量略上升2.0%外,其余主要化学组分含量下降显著。沈利娟等[14]研究了西安市城市降尘和土壤尘PM10和PM2.5中的碳组分空间分布特征,发现不同城市站点降尘中碳组分的分布具有一致性,不同土壤尘中碳组分的差异较大。郭森等[16]研究了石家庄夏季道路尘碳组分特征,发现有机碳(organic carbon, OC)容易在PM10中富集,元素碳(elemental carbon, EC)容易在PM2.5中富集。
西宁市作为兰西城市群中心城市,是西部地区重要的交通枢纽以及工业基地。近年来,西宁市总体环境空气质量稳中有升,但是颗粒物依旧是影响西宁市环境空气质量的首要污染物。窦筱艳等[18]研究发现对西宁市PM2.5影响最大的排放源是城市扬尘,贡献率为26.4%。目前,尚未发现道路扬尘对空气颗粒物贡献的相关研究。本研究通过样方吸尘法于2019年5月采集西宁市353个道路扬尘样品,分析道路扬尘PM2.5 和PM10 中碳组分特征及来源,以期分析西宁市不同道路类型各碳组分分布规律和各源类对道路扬尘的影响,为道路扬尘污染防治政策制定提供参考。
西宁市春季道路扬尘碳组分特征及来源解析
Characteristics and source apportionment of carbon components in road dust in Xining City
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摘要: 为研究西宁市道路扬尘PM2.5和PM10中碳组分的特征及其来源,于2019年5月使用样方法采集西宁市78条铺装道路,通过NK-ZXF再悬浮仪器将样品悬浮到滤膜上,并利用热光碳分析仪测定有机碳(OC)和元素碳(EC)组分。结果表明:PM2.5中ω(TC)为8.49%(环线)~10.38%(支路),ω(OC)为7.68%(环线)~9.36%(支路),ω(EC)为0.74%(国道)~1.02%(支路);PM10中ω(TC)为8.38%(环线)~10.78%(支路),ω(OC)为7.30%(环线)~9.76%(支路),ω(EC)为0.59%(高速)~1.09%(环线)。各类型道路中ω(OC) 均明显大于ω(EC),ω(EC) 在不同道路类型中差异不大。OC在PM10中的质量分数均高于在PM2.5中的值,表明OC更容易富集到粒径大的颗粒物上。采用最小相关系数法(MRS)估算道路扬尘PM2.5和PM10中SOC含量,得出SOC分别占OC总量的81.91%和76.25%。以上结果说明道路扬尘存在明显的二次污染。因子分析和OC/EC比值分析表明西宁市春季道路扬尘PM2.5和PM10主要来源于燃煤、生物质燃烧和机动车尾气排放。本研究可为西宁市道路扬尘污染防治工作及制定环境管理对策提供参考。Abstract: In order to study the characteristics and sources of carbon components in road dust PM2.5 and PM10 in Xining City, samples were collected by the quadrat sampling method at 78 paved roads in May 2019. The samples were re-suspended on filters by using a NK-ZXF sampler, and the concentrations of organic carbon (OC) and elemental carbon (EC) were determined by Thermal Optical Carbon Analyzer. Results showed that the ω(TC) in PM2.5 of road dust was 8.49% (ring road) ~ 10.38% (access road), ω(OC) was 7.68% (ring road) ~ 9.36% (access road), ω(EC) was 0.74% (national highway) ~ 1.02% (access road); ω(TC) was 8.38% (ring road) in PM10 of road dust to 10.78% (access road), ω(OC) was 7.30% (ring road) ~ 9.76% (access road), ω(EC) was 0.59% (expressway) ~ 1.09% (ring road). ω(OC) was obviously greater than ω(EC) for all road types, and ω(EC) did not vary significantly among all road types. The mass fraction of OC in PM10 was higher than that in PM2.5, indicating that OC was more easily enriched to particles with larger particle size. The minimum correlation coefficient method (MRS) was employed to estimate the SOC content in PM2.5 and PM10 of road dust, and it was found that SOC accounted for 81.91% and 76.25% of the total OC, respectively, which indicated that there was significant secondary pollution in road dust. Factor analysis and the OC/EC ratio analysis showed that PM2.5 and PM10 of road dust in spring in Xining City were mainly derived from coal combustion, biomass burning, and vehicle exhaust. This study can provide a reference for preventing and controlling road dust pollution and developing environmental management countermeasures in Xining City.
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Key words:
- Xining City /
- road dust /
- PM2.5 /
- PM10 /
- organic carbon /
- secondary organic carbon (SOC) /
- elemental carbon
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表 1 采样信息
Table 1. Sampling information
道路类型 道路数量 采集样品数量 主干道 26 105 次干道 23 134 支路 21 68 环线 2 9 国道 2 6 高速路 4 31 合计 78 353 表 2 道路扬尘PM2.5和PM10中碳组分因子分析结果
Table 2. The carbon component factor analysis results of PM2.5 and PM10 in road dust
碳组分和
数据类型PM2.5 PM10 因子1 因子2 因子1 因子2 OC1 0.877 0.173 0.662 0.478 OC2 0.895 0.295 0.941 0.138 OC3 0.891 0.329 0.903 0.108 OC4 0.794 0.508 0.872 0.319 EC1 0.806 0.556 0.865 0.430 EC2 0.539 0.745 0.595 0.661 EC3 0.162 0.946 0.103 0.953 OPC 0.690 0.649 0.772 0.462 解释方差 78.262% 10.472% 71.573% 12.040% 累积解释方差 88.734% 83.613% -
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