【作者】 杨柳；

【导师】 郝吉明； 吴烨；

【作者基本信息】 清华大学 ， 环境科学与工程， 2011， 博士

【摘要】 机动车保有量的快速增长对环境空气质量的影响日益被关注。颗粒物是北京环境空气的首要污染物，交通环境中颗粒物污染更为严重，开展交通环境颗粒物污染特征对交通结构响应关系的研究可为未来城市交通发展规划和环境保护政策的制定提供科学依据。本研究选取北四环典型交通环境采样点和密云城市背景点，在常规交通状况和奥运临时机动车管理措施调控的特殊交通状况下开展观测，基于颗粒物质量浓度和粒数浓度及其分布、全化学成分和毒性分析建立了交通环境颗粒物污染特征谱，对不同交通结构下道路边大气颗粒物的来源及其随交通流变化的规律进行了研究，对各项临时机动车管理措施的环境改善效果进行了评估。结果表明，奥运交通状况下北四环PM10、PM2.5和PM1浓度较夏季常规交通状况分别下降12.7%，49.3%和55.4%，PM2.5和PM1较高的浓度降幅反映出交通源排放控制对道路边颗粒物浓度下降的贡献。常规交通状况下北四环PM10、PM2.5和PM1质量浓度逐时变化呈与交通流量耦合的双峰分布；奥运期间随着时均车流量波动的减弱，颗粒物质量浓度逐时变化趋于平缓。奥运交通状况下北四环超细颗粒物粒数浓度约为0.55×104个/cm3，较常规交通状况减少52.2%，来源于汽油车尾气排放和均相成核的成核模态粒子降幅最高。常规交通状况下交通高峰时段超细颗粒物数浓度高于积聚模态粒子，奥运期间全天超细颗粒物浓度均低于积聚模态粒子，表明交通活动超细颗粒物排放大幅削减。全化学成分发现含碳组分对大气颗粒物质量浓度贡献最高。奥运期间北四环OC、EC降幅高于密云，且OC/EC比值高于常规交通状况，反映出柴油货车和黄标车禁行的控制效果。奥运期间交通环境PM2.5中PAHs浓度较常规交通状况下降59%，机动车尾气特征PAH单体浓度昼夜差别被削弱，特征值分析表明柴油车排放削减对PAHs下降的贡献最大。毒性分析发现奥运期间北四环PAHs毒性当量降幅低于浓度降幅，汽油车BaP排放控制是降低交通环境中PAHs健康风险的关键。多元线性回归分析表明污染排放控制对奥运期间北四环PM2.5浓度降幅的贡献高于气象条件改善的贡献。源解析结果显示，奥运交通状况下机动车排放对交通环境PM2.5的分担率显著低于常规交通状况，表明奥运期间机动车一次排放PM2.5的减排力度高于其他污染源。夏季常规交通状况下柴油车尾气对交通环境中PAHs的分担率最高，奥运交通状况下柴油车尾气分担率大幅度下降。上述结果表明，交通流量控制对大气超细颗粒物和PAHs浓度的下降具有显著贡献。更多还原

【Abstract】 The impacts of vehicle emission on ambient air quality have been of great concernbecause of the rapid increase of vehicle counts in megacities. Particulate matter hasbeen the primary air pollutant in Beijing over the past decade. The pollution level isoften found to be more severe in roadside microenvironment than in other urbanbackground areas. Therefore, the correlation analysis between traffic structure and thecharacteristics of particulate matter in the roadside microenvironment could sever as thescientific basis of future decision-making for urban traffic development and airpollution control in megacities in China.In this paper, a typical roadside site (North4thRing Road) and an urbanbackground site (Miyun) were selected; and comprehensive monitoring were conductedin2008~2009with normal traffic structure and special traffic structure regulated by thetemporary traffic control measures implemented during the Beijing Olympic Games(August,2008). Size-resolved mass concentration and number distribution weremeasured using continuous aerosol monitors. Chemical mass balance and toxicequivalency were also calculated for roadside particulate matter. Based on those data,the main sources for roadside airborne particles were identified. Source apportionmentresults with normal and Olympic traffic structures were compared in order to assess theenvironmental improvement effects from different traffic control measures during theOlympic period.With the special traffic structure in August2008, the reduction of average hourlymass concentrations of PM10、PM2.5and PM1at the roadside site were12.7%,49.3%and55.4%, respectively, compared to the non-Olympic summer period (June2008andAugust2009) with normal traffic. Larger reduction of PM2.5and PM1represented thatthe restriction of traffic emissions contributed significantly on the decrease of ambientPM1at roadside site. Bimodal distribution was identified in the diurnal profiles ofparticle mass concentration during the non-Olympic period, with high concentrations inmorning and evening rush hours. This bimodal distribution became flatter during theOlympic period because of the regulation of traffic flow. The average numberconcentration of ultrafine particles at the roadside site was0.55×104particle/cm3duringthe Olympic period, with a52.2%reduction compared to normal traffic exposure. Nucleation mode particles from gasoline vehicle exhaust and homogeneous formationdeclined more than accumulation mode particles. High nucleation mode particle numberconcentration in rush ours, which were found in normal traffic conditions, weredisappeared during the Olympic period, which indicated the significant reduction ofparticle number concentration from vehicle emission.According to the chemical mass balance for roadside particles, carbonaceouscomponents contributed the largest fraction to the total mass of PM10, PM2.5and PM1.During the Olympic period, larger decreases of OC and EC were found at the roadsidesite compared to the background site. Furthermore, the average OC/EC ratio wassignificant higher than that measured with normal traffic structure, which should beattributed to the prohibition of diesel fleet and high-emission vehicles (known as“yellow label vehicles”). The total particulate PAHs calculated under Olympic trafficcondition were59%lower compared to the non-Olympic summer period. The diurnalvariation of vehicle-generated PAHs was also weakened. The restriction of dieselvehicle emission was found contribute the largest fraction for the reduction PAHs levelduring the Olympic period. The total toxic equivalency of particulate PAHs at roadsidesite also decreased with the Olympic traffic structure; however, the reduction was lowerthan that calculated for PAHs mass concentration. Benzo[a]pyrene was found to be thepriority pollutant for the control of PAHs toxicity.Multiple linear regression analysis suggested that the pollution control measureduring the Olympic period accounted for a larger portion of the total variation of PM2.5concentration than meteorological parameters. Source apportionment for PM2.5revealedthat the contribution of vehicle emission decreased during the Olympic period, whichindicated that the reduction of vehicle particle emission was more strengthenedcompared to other sources. For roadside particulate PAHs, diesel vehicle emission wasthe leading source in summer period with normal traffic. During the Olympic period,the contribution of diesel vehicle exhaust significantly decreased. Based on abovediscussion, the restriction of traffic counts and vehicle emission significantlycontributed to the reduction of roadside ultrafine particle concentration and particulatePAHs level.更多还原