大气HONO垂直分布特征及其形成机制研究

As a significant photochemical precursor of OH radical, interest in atmospheric HONO arises from the fact that it plays an important role in enhancing the formation of ozone and photochemical smog. However, the exact mechanisms leading to HONO formation are still not completely understood at present, especially not for its daytime source. Such uncertainties are critical in estimating the contribution of HONO to the HOx budget and therefore to the whole VOC/NOy/O3 chemistry involved in photochemical pollution. There is still a considerable lack of information on typical HONO distribution in both urban and rural environments.. With high primary pollutants and aerosol concentrations, the photochemical system in China can be expected to be sometimes quite different from the one observed in developed countries. To evaluate the atmospheric HONO budget under the prevailing air quality conditions in China, intercomparison among different techniques (IBBCEAS technique and the established DOAS method, etc.) will be performed to validate the performance of all systems for HONO measurement. an incoherent broadband cavity enhanced absorption spectroscopy (BBCEAS) system will be established for atmospheric HONO accurate quantification. Furthermore the method will be applied to investigate the vertical distribution of atmospheric HONO in urban and suburban area. The variation and the vertical distribution characteristics of atmospheric HONO will be investigated. With high NOx emissions in urban area, the evaluation of HONO direct emission via vehicle exhaust will be performed by a tunnel experiment. And the possible formation sources of HONO and its impact to air quality involving regional and complex air pollution in China will be discussed.

HONO作为OH自由基的重要前体物以及对O3和光化学烟雾形成的促进作用而引起广泛关注；关于其来源问题，特别是白天HONO的来源及光化学污染中对HOx基团的贡献以及在整个VOC/NOy/O3大气化学中的角色还存在诸多不确定，各不同大气环境下的数据仍然相当缺乏。. 针对我国一次排放污染物和气溶胶浓度高、成分复杂的大气污染特征，结合国际上普遍关注的大气HONO收支的前沿问题，开展大气HONO测量技术对比，建立准确测量HONO的宽带腔增强吸收光谱（BBCEAS）定量方法。开展城市及城郊大气不同下垫面的HONO垂直梯度观测，通过联合外场实验，揭示我国不同环境大气下HONO的垂直浓度分布信息和变化规律，并针对我国城市区域高NOx排放特征开展隧道实验，探究我国大气复合污染条件下HONO的主要形成途径，评估其对大气复合污染及区域空气质量的影响。

本项目针对目前我国大气复合污染特征，结合国际上普遍关注的HONO 反应途径来源的前沿问题，建立了准确测量HONO 的宽带腔增强吸收光谱（BBCEAS）定量方法并开展HONO 垂直分布观测，分析了我国不同环境大气下HONO 的垂直浓度分布信息和变化规律，探究了我国大气复合污染条件下HONO的主要形成途径。. 通过研究 IBBCEAS 系统参数对 HONO 测量灵敏度的影响，确定了光谱测量的最佳性能参数，通过与光谱学和湿化学方法HONO测量的一致性和准确性对比，建立了准确测量HONO宽带腔增强吸收光谱定量方法，系统在30s光谱采集时间下的探测灵敏度分别为60ppt和100ppt（1δ）。采用宽带腔增强系统结合325m气象观测塔的吊舱平台测量了HONO和NO2的高分辨率垂直廓线，获得了我国城市环境下大气HONO的垂直浓度分布信息和变化规律，分析了直接排放、气溶胶表面非均相反应和地表非均相反应对观测地点夜间HONO的贡献，探究了观测地点夜间HONO的主要来源。边界层内HONO和NO2有明显负梯度变化。气溶胶表面NO2非均相转化HONO浓度累积不足以解释高空HONO浓度水平，HONO主要来源于地面交通和地表NO2非均相转化，然后传输到高空。雾霾期间，午夜时段（22:30-01:30）随着边界层的发展，HONO的干沉降损耗和地表扩散和输送达到平衡，夜间地表面即是HONO的源也是汇。清洁期间和雾霾期间的地面HONO产率分别为0.13和0.12，表明每8-9个NO2分子沉降会释放1个HONO到大气中。同时本项目研制了一种双动态箱系统，首次结合宽带腔增强吸收光谱(BBCEAS) 系统成功应用于华北平原农田中的HONO排放通量测量。通过2017年在河北望都县的农田HONO通量外场观测，获得了施肥期间HONO排放通量。农业施肥的初期会导致土壤高浓度的HONO排放，HONO高排放期间，HONO通量表现出明显的日变化，计算最大值达到10-5mol·m-2·h-1，比文献中报道的外场观测结果高一个数量级，排除了来自与NO2相关的均相和非均相反应，揭示了农业施肥活动具有很强的HONO排放潜势。