大气化学氧化过程对中重度雾霾持续时间的影响

Fog and haze weather is one of the severe weathers. This weather will affect atmospheric visibility, industrial and agricultural activities, transportation, human health and ecological environment. The heavy fog and haze is harmful, and it often arouses a great public concern. It has been shown that the frequency and duration of fog and haze episode increased obviously in China in recent years. However, the available knowledge is not enough to understand these phenomena. Currently, it is difficult for one to control the atmospheric physical processes, such as the wind speed and wind direction, to shorten the duration of the fog and haze episode. It seems to be a feasible way to shorten the fog and haze duration by changing the chemical processes that affect the fog and haze formation and evolution. The present project plans to study the evolution of the fog and haze particles in the atmosphere from the perspective of atmospheric chemistry. Our work will mainly focus on the change of components in particulate matter in heavy fog and haze episodes due to the atmospheric oxidation processes and the relationship between the particle oxidation and duration of fog and haze episode. We will employ a field reactor to investigate the reactions of oxidation, photolysis, and trace-gases uptake on the particles through online sampling the ambient particles during heavy fog and haze episodes. On the basis of the obtained particlar and gaseous components concentrations and the meteorological conditions, the results of field reaction experiments, as well as the gas-particle partitioning and deposition models, we will make an evaluation on how the particle oxidation affect the duration of fog and haze episode. The output of this project will provide the useful physical and chemical parameters which can be used in the fog and haze model, and benefit the control measurements for the heavy fog and haze.

雾霾天气是灾害性天气之一，对大气能见度、工农业活动、交通运输、人体健康和生态环境产生诸多不利影响。严重雾霾天气危害很大，往往引起公众的极大关注。近年来我国雾霾天出现频次增加，持续时间增长，但原因尚不完全清楚。目前，人们很难通过人工改变风速风向等物理过程来缩短雾霾的持续时间。通过改变影响雾霾形成和演变的化学过程来减轻雾霾则可能是一条可行的途径。本项目拟从大气化学角度出发，研究雾霾颗粒物在大气中演变规律，着重研究中度和重度雾霾天气中颗粒物在大气氧化过程中其组分变化与雾霾持续时间的关系。通过分析雾霾颗粒物关键组分，并现场实验研究雾霾颗粒物氧化反应、光解反应以及微量气体与雾霾颗粒物反应，以雾霾观测和实验研究结果为基础，结合文献调研和气象条件分析，利用气－粒分配和颗粒物沉降模型等评估氧化反应与雾霾持续时间的关系。研究结果为雾霾大气模式提供有用的物理化学参数，为预警和治理中度和重度雾霾提供科学依据。

雾霾天气是灾害性天气之一，对大气能见度、工农业活动、交通运输、人体健康和生态环境产生诸多不利影响。严重雾霾天气危害很大，往往引起公众的极大关注。近年来我国雾霾天出现频次增加，持续时间增长，但原因尚不完全清楚。本项目从大气化学角度出发，开展这一方面研究。我们通过对大气氧化剂、羰基化合物与PM2.5颗粒物之间关系的外场观测研究，以及微量气体（过氧化物、二氧化硫、挥发性含氧有机物）在颗粒物表面非均相反应动力学特征和机理的实验室模拟研究，探究中度和重度雾霾持续时间的化学机制。研究发现颗粒物表面具有强氧化能力，即使在气态氧化反应受到抑制的条件下，也能使二氧化硫（SO2）和含氧挥发性有机物（OVOCs）发生非均相氧化反应生成二次颗粒物组分，增加颗粒物质量浓度，使得雾霾得以持续。颗粒物的氧化能力主要来源于两个方面。① 颗粒物表面固有的氧化能力。矿质颗粒物表面含有的活性位点（羟基基团和晶格氧）和过渡金属（Fe、Cu、Mn和Ti等）能与到达表面的反应性气体（SO2、OVOCs等）发生反应。② 大气气态氧化剂在颗粒物表面摄取和转化。本研究发现PM2.5颗粒物能够有效地摄取过氧化物，过氧化氢（H2O2）和过氧乙酸（PAA）的摄取系数为10–4量级；还发现有机过氧化物可以在二次有机气溶胶（SOA）表面发生快速转化生成H2O2。颗粒物也能够摄取HO2自由基，并使HO2自由基在颗粒物表面生成H2O2。H2O2和HO2自由基非均相反应增强了颗粒物表面氧化能力。颗粒物从气相中摄取氧化剂（H2O2等）与颗粒物表面固有氧化能力相结合，显著促进SO2和OVOCs非均相反应生成二次硫酸（盐）和SOA，使得这些二次颗粒组分在颗粒物表面不断累积，从而导致颗粒物质量浓度增长，加重和持续雾霾天气。本研究为大气雾霾形成机制研究和大气化学模式研究提供了重要的基础数据以及新的化学动力学参数和反应机理，为预警和治理中度和重度雾霾提供科学依据。