发光二极管LED非相干宽带腔增强吸收光谱技术对大气HONO的定量方法研究

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 prevaliling air quality conditions in China, an incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) system based on LED light source will be established for atmospheric HONO quantification. To ensure the system optimal performance with high sensitivity for spectroscopic identification, the effects of the system parameters on HONO measurement will be investigated. In order to caculate the concentrations of trace gases, a multi-component concentration retrieval algorithm will be developed. Furthermore the method will be applied to the in-situ detection of HONO and NO2 with high sensitivity in real atmosphere. Intercomparison between IBBCEAS technique and the established DOAS method will be performed to validate the performance of both systems for HONO measurement. The levels and the variation characteristics of atmospheric HONO and its possible formation sources will be investigated under different environment conditions.

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，开展发光二极管非相干宽带腔增强吸收光谱（LED-IBBCEAS）技术对大气HONO的定量方法研究，通过研究系统参数对测量灵敏度的影响，确定光谱测量最佳的性能参数，建立应用于IBBCEAS技术的多组分痕量气体浓度反演算法模型，实现对大气HONO及NO2等痕量成分的实时在线高灵敏探测，通过与已有的差分吸收光谱（DOAS）技术进行比对、验证，开展我国不同大气环境下HONO浓度分布特征研究，探究不同大气环境下HONO的来源途径。

本项目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，开展发光二极管非相干宽带腔增强吸收光谱（LED-IBBCEAS）技术对大气HONO的定量方法研究。通过研究非相干宽带腔增强吸收光谱（IBBCEAS）系统参数（光源稳定性、光源耦合效率、增强腔壁效应及采样损耗、光谱波段选择及气体交叉干扰等）对HONO测量灵敏度的影响，确定了光谱测量的最佳性能参数，评估了增强腔镜片反射率标定方法，结合多组分痕量气体浓度反演算法模型，建立了基于365nm发光二极管（LED）光源的非相干宽带腔增强吸收光谱（IBBCEAS）HONO测量系统，实现对大气HONO 及NO2等痕量成分的实时在线高灵敏探测。系统在60s光谱采集时间下的探测限分别为80和150ppt（2σ）。与湿化学点式采样以及已有的差分吸收光谱（DOAS）等技术进行比对、验证，IBBCEAS系统测量结果与上述方法显示了较好的一致性。. 通过2014年在河北望都县开展的国际外场观测以及2014/2016年在北京怀柔国科大校园开展的外场观测，获得了不同大气环境下HONO浓度分布特征，对夜间NO2非均相反应以及交通来源对HONO的贡献开展分析。两地实验中均发现夜间NO2非均相反应中水汽的增加会加速提高该反应转化速率，但过高的水汽浓度（>75%）会阻碍该反应，而颗粒物浓度的变化对测量期间NO2非均相反应生成HONO的途径影响较小。在受交通影响相对较大的怀柔站点，测量期间观测到来自直接排放途径的平均贡献率达到了30%；在交通影响较小的望都站点，白天观测到HONO最高浓度可达到3ppb，计算的HONO未知源强可达到14ppb/h，排除其来自于非均相以及交通排放的影响，推断该未知源可能与当地农业活动有关。