重庆城区PM2.5的化学组成特征及其大气消光贡献研究

Based on high-resolution, real-time measurement, intensive speciation sampling and bulk chemical analysis of fine particulate matter over three consecutive years in three typical urban areas in Chongqing, the characteristics of temporal and spacial variations in chemical species of PM2.5 will be investigated and PM2.5 speciation reconstructed. Chemical extinction algorithm will be further extracted on a seasonal basis to apportion visibility impairment (measured light extinction) to each speciation. By examining the time series of PM2.5 speciation constitutions and comparing their variations during the periods of 20% best and 20% worst visibilities and over the process of typical haze growth and fadeaway, the primary haze-related chemical speciation in PM2.5 is to be determined. Furthermore, chemogenic formation of haze is to be assessed preliminarily by combining real time measurements of size distribution, major chemical species of particulate matter, gaseous precursors, meteorological parameters, and back trajectories of air masses over the study period. This information, together with the source apportionment of each species and modeling of emission reduction episodes, has implications for working out the control countermeasures and implementation plans to bring to fine particle standard with the best visibility improvement. It is anticipated that the study results will enhance understanding of the reasons for heavy haze formation from a point of PM2.5 chemical extinction, which is reconstructed on the basis of speciation sampling and extensive high-resolution measurements. The study will provide valuable scientific basis for simultaneous control of fine particulate pollution and improvement of visibility, and serve as a methodology for reference as well.

选取重庆市3个典型城区环境，基于持续3年在各季节同步进行化学物种采样与全组分分析，结合高分辨率在线观测，系统分析PM2.5化学组成的时空变化特征并重构PM2.5的化学物种；通过回归建立基于季节的PM2.5化学消光算法，定量解析各物种对能见度降低的影响；通过剖析PM2.5化学物种构成的时间序列特征和对比分析其在能见度最高与最低的20%日及典型霾的生消过程中对消光的贡献，提取典型霾的PM2.5特征化学物种指标；进一步结合对在线测量的颗粒物粒径分布、成分与特征比值以及气态前体物和气象参数的分析、气团后向轨迹的模拟，对典型霾的成因进行诊断。这对于进一步结合源解析，合理制定对于改善能见度效果最好的PM2.5达标对策及实施进程而言十分关键。项目可望从综合化学物种采样和高分辨率测量重构PM2.5化学消光的角度丰富我国霾的成因研究，可为同时有效控制PM2.5污染和改善能见度提供科学依据和方法学上的借鉴。

基于持续3年在重庆典型城区/郊区的PM2.5化学物种采样/全组分分析并结合高分辨率观测和卫星遥感等，初步明晰了重庆地区PM2.5质量浓度和化学组成的时空变化特征；通过化学物种重构和消光算法解析了PM2.5的化学消光贡献；通过关联大气物理与大气化学特征，初步探究了典型重霾污染生消过程及成因。.重庆地区PM2.5浓度呈现下降趋势，但仍处于较高的浓度水平；冬季PM2.5污染最为严重，平均浓度约为其它季节的2倍。PM2.5浓度及其主要化学组分含量的空间分布呈现重庆主城区、涪陵城区>万州城区>缙云山。二次无机离子和含碳组分是PM2.5的主要化学组分，共占PM2.5质量的70%-84%。SO42-和NO3-年均浓度（2015年分别为10.3 μg/m3、5.8 μg/m3）较10年前分别下降59.8%和上升5.2%，与其前体物排放量此消彼长的趋势一致；NO3-/SO42-浓度比则由~0.2升至~0.5，表明固定源和流动源对PM2.5的贡献也呈现类似的变化。.修订后的IMPROVE算法分季节重构消光系数适用于重庆地区。PM2.5中 (NH4)2SO4对能见度降低的贡献最大（32.3%~56.1%），其次为NH4NO3（21.0%~28.5%）和有机物OM（17.5%~29.8%），而EC和FS的贡献之和低于10%。霾污染主要发生在冬季且伴随频繁出现的静稳天气。在PM2.5浓度快速增长过程中，二次组分的贡献显著增加，且NO3-的增长率往往高于SO42-。这有别于我国东部地区观测到的硫酸盐爆发性增长现象。有机组分示踪物分析及单颗粒气溶胶成分在线观测均表明，在秋冬季重污染期间生物质燃烧的贡献加大。为同时有效降低高相对湿度条件下重庆城区PM2.5浓度并提高能见度水平，应更为严格地实施一次PM2.5及气态前体物（NOX、NH3、SO2和VOCs）的协同减排，并加强对流动源排放和秋冬季生物质燃烧的控制。