氢氧自由基（OH）是大气中最重要的氧化剂之一，其反应活性是大气氧化能力强弱的标志。OH所引发并参与的氧化反应过程是以VOC为代表的大气污染物的主要降解途径，也是导致二次有机气溶胶和地表臭氧（O3）生成的重要机制。充分了解大气氧化能力，即OH自由基的来源特征及其相对贡献，是深度解读我国灰霾及光化学烟雾生成机理的根本途径。本项目拟使用化学电离质谱仪、光化学通量谱仪（290-660 nm）等先进观测技术对南京及周边地区大气中O3、甲醛（HCHO）、乙醛（CH3CHO）、亚硝酸（HONO）、VOC、氮氧化物（NOx）以及光分解频率进行高时间分辨率、高灵敏度的外场测量，获得OH主要前体物的时空分布和季节变化规律，并结合其它常规数据使用美国国家大气研究中心开发的MM化学模式评估各前体物对OH产率的贡献并区分一、二次源的相对强度，为制定有效的大气污染物减排、控制政策提供依据。

Hydroxyl radical (OH) is one of the most important oxidants in the atmosphere. OH reactivity indicates the strength of atmospheric oxidative capability. Atmospheric oxidation processes initiated and participated in by OH are the major degradation paths for air pollutants, especially the volatile organic compounds (VOCs), and are the essential mechanisms that drive the formations of secondary organic aerosol and ground level ozone (O3). Detailed understanding of the atmospheric oxidation capability, i.e., the characterization and apportionment of OH sources, is the fundamental way to fully elucidate the mechanisms underlying the formations of haze and photochemical smog in China. This project is proposed to perform field observations of O3, formaldehyde (HCHO), acetaldehyde (CH3CHO), nitrous acid (HONO), VOCs, nitrogen oxides (NOx), and photolysis frequencies in Nanjing and the surrounding area with high temporal resolution and high sensitivity using state-of-the-art instrumentations, including chemical ionization mass spectrometry and spectroradiometry (290-660 nm). The goal is to obtain the spatial, temporal and seasonal variation profiles of the major OH precursors. Using NCAR Master Mechanism (MM) box model constrained with the observation results, the detailed contribution of each precursor to the OH production will be evaluated and the primary and secondary sources will be resolved. The findings from this work will provide the bases for the formulation of effective air quality management and emission control strategies.