【作者】 严晗；

【导师】 吴烨；

【作者基本信息】 清华大学 ， 环境科学与工程， 2014， 硕士

【摘要】 机动车排放已成为中国特大型城市空气污染的主要来源之一。道路交通环境的污染物浓度往往高于城市平均水平，对人体健康影响更为显著。因此，研究典型道路机动车排放及道路边污染物浓度特征，在城市大气污染防治工作中占有重要地位。研究对北京多条典型道路交通流进行了实地采样和分析，确定了包括小时总车流量、车型分布和外地货车比例等重要参数，并调研了平均速度和技术构成等交通流信息。应用EMBEV模型，计算了典型机动车污染物NOX、PM2.5和BC的平均排放因子和排放强度。在此基础上，进一步模拟了典型道路排放对道路边的污染物浓度贡献，并就模型选用、外地货车比例和气象条件的影响进行深入分析。采样各路段小时车流量呈现早晚高峰的特征。由于北京实施货车区域限行政策，夜间货车流量大幅上升，导致三种污染物时均排放因子的峰值在夜间出现，并与重型柴油车（如大型客车、公交车和货车）占总车流的比例强烈相关（R2>0.96）。而时均排放强度则受到早晚高峰车流及夜间排放因子升高的叠加影响，导致时均排放强度的昼夜差距较小时车流量显著缩小。以2012年南三环为例，其BC单车平均排放因子峰值出现在夜间货车驶入时段，接近40mg/km，而BC排放强度峰值出现在早晚高峰期，高达100g/(km·h)。由于外地货车控制水平较差，其对夜间颗粒物排放强度的影响显著。以北四环和南三环为例，最多可增加50%~60%的排放量。研究利用CALINE模型和AERMOD模型对北四环中路机动车排放对道路边BC浓度贡献进行了模拟，结果表明AERMOD模拟结果能够体现昼夜间的差异，并与同步空气质量监测规律更吻合。以北四环为例，2009年夏季昼夜BC贡献浓度分别为1.6±2.7μg/m3和3.3±1.4μg/m3，冬季昼夜则分别为3.4±4.1μg/m3和3.7±4.6μg/m3。对于市区道路，昼间小型客车和公交车浓度贡献率最高，夜间货车的浓度贡献率最高。夜间和冬季不利的气象条件是导致污染物浓度贡献急剧升高的更为重要的因素。考虑外地进京货车，夜间BC平均浓度贡献高达5.6μg/m3。若这部分外地进京货车在扩散条件较好的午间时段驶入市区，夜间BC浓度贡献可控制在2μg/m3以下，而午间BC浓度仅增加0.2μg/m3。综合考虑排放强度、昼夜间气象扩散条件和交通运行状况制定更合理的控制政策，对改善城市空气质量显得尤为重要。更多还原

【Abstract】 On-road vehicles have been identified as one of the major sources of urban airpollution for megacities in China. In particular, the curb concentrations of traffic-relatedpollutants are in general higher than the urban average, leading to more significant publichealth effects. Therefore, characterizing vehicle emissions and curb concentrations ofvehicular pollutants for typical roads is essential to mitigate urban air pollution.In this research, field investiagtion of real-world traffic flow data were conducted ontypical roads in Beijing to derive key inputs, including hourly profiles for total trafficvolume, fleet composition by vehicle category, and proportion of on-road trucks registeredin other provinces except Beijing (i.e., outsider trucks). Average speed information hasbeen also collected from previous studies. The Emission Factor Model for the BeijingVehicle Fleet (EMBEV) was applied to estimate emission factors and emission intensity ofNOX、PM2.5and BC for those typical roads. Furhermore, the curb concentrations ofprimary vehicular popllutants were simulated with special attentions paid to theapplicability of dispersion models, meteorolical effects and potential contribution by thoseoutsider trucks with higher PM2.5and BC emission factors.Our results show that two peaks of hourly traffic volume occoured during morning andevening rush period for each road. Average hourly emission factors of NOX, PM2.5and BCwere strongly correlated with hourly volume proportions of heavy-duty diesel vehicles (e.g.,diesel buses and trucks). However, hourly total traffic volumes and the higher emissionfactor during the night time both impacted emission intensity results. Taking the SouthThird Ring Road for example, the peak of hourly average BC emission factors, about40mg/(km·veh), occured during the night time when trucks were allowed to drive withinurban aera. On the other hand, the peaks of hourly BC emission intensity occurredsychoronically in the morning and evening rush period, appriximately100g/(km·h). Theimpact of outsider trucks was significant to emission intensity during night time. Taking theNorth Fourth Ring Road and the South Third Ring Road for example,50%~60%ofemission might increase. Two models, the CALINE3and the AERMOD, were applied to estimate curbconcentrations of vehicle-emitted pollutants (e.g., NOX, PM2.5and BC). Results showedthat the AERMOD could provide more reasonable simulations compared to the CALINE3based on the real-time air quality monitoring data. Taking BC for example, simulatedaverage BC concentration contributed by primary vehicle emissions during the day andnight time of summer period were1.6±2.7μg/m3and3.3±1.4μg/m3, respectively, for theNorth Fourth Ring Road as of the year2009. In winter period, simulated concentrationsincreased to3.4±4.1μg/m3and3.7±4.6μg/m3, respectively. For urban roads, light-dutypassenger cars and diesel buses were leading contributors among all vehicle categories tocurb BC concentration during the day time. During the night time, diesel trucks became thedominant contributor. The unfavorable dispersion conditions during the night time and thewinter time have been identified the more important factor leading to higher curb pollutantconcentrations. Futhermore, if the outsider trucks are taken into account for the NorthFourth Ring Road during the night time, the average BC concentration contributed by on-road vehicles can rise to5.6μg/m3during the night time. If all those outsider trucks driveinto urban area during the noon period, when the dispersion conditions are usually mostfavorbale, the traffic-contributed BC concentrations during the night time can be controlledbelow2μg/m3, with a very slght increase of BC concentration (~0.2μg/m3) during thenoon period. Our research can improve the understanding of policy-makers for controllingvehicle emissions and urban air pollution in the future.更多还原