北京城市环境大气挥发性有机物的来源及二次转化研究

Volatile organic compounds (VOCs) are the key precursors for both secondary organic aerosol and ozone in the troposphere. Low volatile organic compounds (LVOCs) formed from VOCs degradation are crucial for understanding both VOCs degradation mechanism and nucleation and growth of particles. Formation mechanism of LVOCs is also the frontier area in atmospheric chemistry community. Based on observation at forest stations, such as Hyytiälä, it has been found that LVOCs from oxidation of terpenes play an important role in particle nucleation and growth. In China, the contribution of different sources, such as coal combustion, vehicle exhaust and so on, has been illustrated by different research groups in certain terms and places including Beijing-Tianjin-Hebei area, Yangtze River Delta and Pearl River Delta. However, at the present time, simultaneous observation studies on both LVOCs and VOCs has not been deployed in China. At the same time, field observation related to LVOCs has not been performed under typical urban environment even in Europe and North America. In this study, observation and source apportionment of LVOCs and VOCs will be carried out simultaneously at the west campus of Beijing University of Chemical Technology (98 Zizhuyuan Road, Haidian district), where a super observation station has been set up, using state-of-the-art instruments including a soft photon ionization mass spectrometer, an atmospheric pressure interface-chemical ionization mass spectrometer and other instruments. The mechanism of VOCs degradation and LVOCs formation as well as uptake kinetics of typical LVOCs will be further investigated combining with a smog chamber and flow tube reactor. This study will provide important parameters for understanding particle formation and growth under urban environment. It will also be helpful for understanding the formation mechanism of the air pollution complex in Beijing.

挥发性有机物(VOCs)是二次有机气溶胶和臭氧的重要前体物。低挥发性有机物(LVOCs)是VOCs的降解产物，其对揭示VOCs降解和颗粒物成核与增长机制都具有重要意义，也是国际大气化学领域的研究前沿。国外在森林站研究发现，萜烯氧化生成的LVOCs对颗粒物成核增长有重要作用；我国研究人员在京津冀、长三角和珠三角地区等地获得了特定时段VOCs的特征和来源。但国内尚未开展LVOCs和VOCs的同步在线观测和源解析研究，国际上也未针对城市大气环境开展LVOCs在线观测研究。本项目拟利用光电离飞行时间质谱和大气压化学离子化飞行时间质谱等先进手段，在北京化工大学西校区开展VOCs和LVOCs的持续在线观测和源解析研究，结合烟雾箱和流动管等研究典型城市环境VOCs的降解过程及LVOCs的生成机制，测定LVOCs在典型颗粒物上的摄取系数，为认识城市环境条件下颗粒物成核和增长过程提供关键参数。

针对北京城市环境大气挥发性有机物的来源、二次转化及影响，在北京化工大学西校区、北京石油化工学院等多地开展了观测研究，获得了典型挥发性有机物(苯系物、烃类和卤代烃等)、低挥发性有机物的浓度特征和季节性变化规律。利用受体模型源解析方法发现夏季植物源排放对VOCs具有重要贡献，冬季人为源（机动车尾气、溶剂使用等）是VOCs的重要来源；VOCs氧化降解是高含氧有机物(OOMs)的主要来源，而有机硝酸盐是OOMs的主要组成部分，其浓度是其他OOMs的2.7~3.4倍，且具有夏季>春季>秋季>冬季的季节变化规律；人为源C6-9的烷基苯类OOMs在所有OOMs中的占比约达50%，是北京OOMs的主要贡献者；识别了北京不同天气过程挥发性有机物的主要源和二次转化过程，探讨了不同污染天气过程中挥发性有机物和LVOCs 的生消规律及其对新粒子生成事件、霾污染过程的贡献，发现气团老化程度对新粒子生成和霾污染过程具有显著影响。北京城市环境人为源芳香烃化合物经OH氧化是冬季OOMs和二次有机气溶胶的生成主要途径，HONO光解是北京冬季污染天OH的重要来源，尤其是冬季污染天HONO产生OH的速率为2.431.21 ppbv h-1，明显高于O3光解的速率1.451.49 ppbv h-1。HONO和甲苯浓度的消耗和有机气溶胶浓度的升高与传统的烟雾箱实验过程中污染物浓度的变化曲线高度相似。在冬季非污染和污染时期，OOMs在颗粒物上的凝结对有机气溶胶质量浓度增长速率的贡献分别为26%和39%。在夏季，异戊二烯光化学消耗对臭氧生成和OOMs都有重要贡献，这与OH、HO2和RO2自由基的生成速率显著增加密切相关。此外，含氧有机物的液相化学过程，也是北京二次有机气溶胶生成的重要途径。研究结果为揭示北京市大气污染成因提供了科技支撑，提出北京开展臭氧和PM2.5防治，需根据季节开展差异化的VOCs控制策略。项目资助发表论文22篇(SCI收录21篇)，其中一标注论文11篇(SCI收录10篇)，授权专利2件，培养博士研究生1名，硕士研究生2名，在读博士3名。