基于实测的京津冀及周边地区机动车刹车磨损大气颗粒物及重金属排放特征与环境效应研究

Brake wear of vehicle is an important contributor to the emissions of airborne particulates as well as the associated hazardous heavy metals in urban areas. Along with industrial structure optimization and backward productivity elimination, the adverse effects of airborne particulate as well as associated heavy metals originating from brake wear on environmental air quality and human health will further increase in the near future. Therefore, study on emission characteristics and environmental effect of airborne particulates as well as associated heavy metals from brake wear of vehicle based on experimental measurements is really imminent. In this study, the database of emission factors of airborne particulates (TSP, PM10 and PM2.5) as well as associated heavy metals (e.g., Cu, Sb, Zn, Fe, Pb, Cr, etc.) from brake wear of vehicle in the Beijing-Tianjin-Hebei (BTH) region and surround areas will be established based on experimental measurements, so as to master the particle size distribution and chemical speciation of target pollutants. Based on urban road network in study area, the regional emission inventory of target pollutants with a high resolution of 1 km × 1 km is developed by combing the relevant activity levels, in order to interpret the emission characteristics of target pollutants from brake wear of vehicle. Further, by sample collecting and analyzing of different brake wear debris, the migration and transformation mechanism of hazardous heavy metals during braking process will be revealed. On the basis of field tests and high resolution emission inventory, the environmental effect of airborne particulates as well as associated heavy metals emissions from brake wear of vehicle will be assessed by using combination of receptor model and diffusion model. Consequently, results of this study can supply essential information on implementing regional complex air pollution control and comprehensive prevention of heavy metals pollution in China.

机动车刹车磨损是城市环境大气颗粒物及有害重金属排放的重要贡献者。伴随产业结构优化和落后产能淘汰工作的推进，刹车磨损对城市环境空气质量及居民健康的影响将进一步增大，开展基于实测的机动车刹车磨损大气颗粒物及重金属排放特征与环境效应研究迫在眉睫。本研究基于现场实测建立机动车刹车磨损大气颗粒物（TSP、PM10和PM2.5）及重金属（Cu、Sb、Zn、Fe、Pb、Cr等）本地化排放因子集，解析刹车过程中大气颗粒物及重金属的粒径分布特征和赋存形态，结合地区活动水平构建京津冀及周边地区基于城市路网的1 km × 1 km网格化大气排放清单；通过对不同磨损产物开展样品采集和分析，揭示重金属迁移转化机制；结合道路敏感点环境介质采样分析和高时空分辨排放清单，综合扩散模型和受体模型的耦合运用，评估机动车刹车磨损大气颗粒物及重金属排放的环境效应。本研究可为区域复合大气污染控制和重金属污染防治提供基础数据支撑。

机动车刹车磨损是城市环境大气颗粒物及有害重金属排放的重要贡献者。本研究使用ICP-MS和IC获得我国典型刹车片中30种元素和8种无机离子的含量分别约为0.5-120943.9 ppm和262.2-5841.5 ppm。综合现场实测、文献调研和实验室元素分析获得的本地化排放因子集，结合地区活动水平，本研究构建了2000-2018年京津冀及周边地区机动车刹车磨损TSP、PM10、PM2.5和10种金属元素大气排放清单，结果表明2018年地区机动车刹车磨损TSP、PM10、PM2.5和10种金属元素排放量分别约为15894.7 t、12854.1 t、3894.2 t和2726.8 t，2000-2018年间年均增长率约为10.3%；小型/微型客车和山东是2018年机动车刹车磨损颗粒物及金属元素排放的最高车型和省份，排放占比分别约为56.3%和31.9%。北京、唐山、天津、郑州和青岛是地区机动车刹车磨损颗粒物及金属元素排放量最高的5个城市，排放占比约为25.8%。选择与车流量、刹车频率等因子存在交互作用的信息点（POI）为分配指标，利用ArcGIS构建了典型城市基于城市路网的0.5 km × 0.5 km的颗粒物及金属网格化大气排放清单，城市中心区因刹车频繁为高排放区域，以TSP排放为例，北京和天津单位平方公里TSP排放量的最高值分别约为13119.5 kg/ km2和60615.1 kg/ km2。基于对磨损碎屑的形貌和物相分析发现，在汽车制动过程中常伴有氧化反应发生，刹车片中的Sb2S3、Fe2O3等物质可被氧化为Sb2O3和Fe3O4，并赋存于磨损碎屑中；磨损碎屑50%质量分数处的颗粒物粒径平均值约为21.3 μm，PM10和PM2.5的形成率分别约为43.8%和5.9%；金属元素在0-2.5 μm、2.5-10 μm和>10 μm的颗粒中的质量分数分别约为5.9%、37.9%和56.2%。PCA和PMF解析结果表明刹车磨损为道路尘的主要贡献源之一，不同类型道路的道路尘中11种金属元素在弱酸提取态、可还原态、可氧化态和残渣态中占比分别约为5.7-7.8%、5.9-12.1%、21.5-32.9%和55.3-74.1%；在道路尘中来自刹车磨损贡献的金属元素Zn、Cu等元素分别具有高环境风险和中等环境风险。本研究可为区域复合大气污染控制和重金属污染防治提供基础数据支撑。