大气NO3自由基和N2O5的高灵敏探测方法研究

NO3 radical is known as a dominant oxidant in the atmosphere at night, its chemical process attracts more and more attentions. N2O5 is an important reaction intermediate in nocturnal nitrogen oxidation process, and also temporary reservoir for NO3 radical. Due to the extremely low concentration and the limitation of the detection method of NO3 radical and N2O5, the data for concentration measurement and nocturnal chemical process research of NO3 radical and N2O5 in different atmospheric condition is insufficient, its atmospheric chemical behavior has lots of uncertainty. . This project is aimed to utilize the diode laser cavity ring-down (CRD) spectroscopy for the high sensitivity quantitative detection of atmospheric NO3 radical and N2O5. A dual-cavity ring-down detection system is built, which uses the diode laser as light source, and the influence caused by different system parameter for NO3 radical and N2O5 measurement is tested. The method of calibration of the loss in the inlet system is discussed, and the accurate measurement of the loss is carried out for the CRD system. After studying the NO3 radical and N2O5 detection sensitivity by CRD technology, synchronous real-time online measurement of NO3 radical and N2O5 with high sensitivity and high time resolution are achieved. Using the steady state approximation, NO3 radical and N2O5 steady-state lifetimes in different environment are analyzed. Nighttime loss mechanism of NO3 radical and N2O5 uptake coefficients are investigated, and further analysis of NO3 radical and N2O5 nocturnal chemical process are carried out.

NO3自由基是夜间大气最重要的氧化剂，其化学过程备受关注；N2O5是氮氧化物夜间大气化学过程中重要的反应中间体，也是NO3自由基的临时储库。由于它们的浓度比较低及一般探测方法的局限性，大气NO3和N2O5的测量方法及其夜间化学过程研究都相当缺乏，其大气化学行为具有较多不确定性。.本项目拟采用二极管激光腔衰荡光谱技术研究大气NO3自由基和N2O5高灵敏定量探测问题。建立二极管激光双腔式腔衰荡光谱(CRD)探测系统，研究系统参数对NO3和N2O5测量的影响；探究进气损耗标定方法，准确标定系统进气损耗。通过开展实验室CRD系统测量灵敏度研究，实现大气NO3和N2O5的同步实时在线高灵敏探测。采用稳态近似法分析不同环境下NO3和N2O5的稳态寿命，探究国际上普遍关注的NO3自由基夜间损耗机制和N2O5气溶胶表面多相沉降的摄取系数及其影响因素，并进一步分析NO3自由基和N2O5的夜间大气化学过程。

NO3自由基是夜间大气最重要的氧化剂，其化学过程备受关注；N2O5是氮氧化物夜间大气化学过程中重要的反应中间体，也是NO3自由基的临时储库。由于它们的浓度比较低及一般探测方法的局限性，大气NO3和N2O5的测量方法及其夜间化学过程研究都相当缺乏，其大气化学行为具有较多不确定性。.本项目基于二极管激光腔衰荡光谱方法开展了环境大气NO3自由基和N2O5的高灵敏探测技术研究。重点解决了低损耗采样、光源与高反腔的高效耦合、弱信号探测及数据处理等关键问题，研制了腔衰荡探测系统（NO3/N2O5-CRDS），实现了NO3自由基和N2O5的高灵敏测量，探测限分别为2.3ppt（2.5s）和3.1ppt（2.5s），测量误差分别为8%和15%。首次建立了NO3自由基和N2O5的采样损耗标定方法，突破了实验室N2O5的高纯度合成问题，解决NO3自由基没有标准气体的难题；研制了相应的标定系统，实现了对NO3/N2O5-CRDS探测系统进气损耗的准确标定。开展了综合外场观测实验，准确获得了不同大气条件下（京津冀/长三角，城市/郊区）NO3自由基和N2O5的浓度分布和变化特征；采用稳态近似法分析了不同环境下NO3自由基和N2O5的稳态寿命；探究了NO3自由基对BVOC氧化和N2O5气溶胶表面非均相反应的摄取系数及其影响因素，并进一步分析了NO3自由基和N2O5损耗速率及直接损耗占比，明确了夜间硝酸盐生成速率及NOx沉降机制。.本项目的开展解决了夜间大气化学过程的关键探测技术瓶颈，推动了夜间自由基化学研究的全面开展，提升了夜间大气化学研究能力，促进了对大气复合污染成因的精细认知，对于认识我国区域性污染形成和改善空气质量具有重要作用。