城市大气NO3自由基和N2O5的夜间化学过程研究

NO3 radical and N2O5 are key species of the nighttime tropospheric chemistry, that play a central role in the tropospheric chemistry issues such as atmospheric self-cleaning capacity, secondary aerosol formations, Nitrogen Oxides removal mechanism, etc. Due to the extremely low concentration, high reactivity and short life time, 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 carry out the field observation of NO3 radical and N2O5 in the urban area. Low loss sampling technique is studied for atmospheric environment of high particulate matter. The calibration method of the loss in the inlet system is discussed for accurate measurement. Synchronous real-time online measurements of NO3 radical and N2O5 with high sensitivity and high time resolution are achieved. Using the non-steady state approximation, NO3 radical and N2O5 lifetimes in different environments are analyzed. Nighttime loss mechanism of NO3 radical and its contribution to the SOA formation are investigated. N2O5 uptake coefficients in aerosol surface settlement are studied, and the relationship between the N2O5 non homogeneous reaction and nitrate, sulfate, humidity (etc.) is analyzed. Further analysis of NO3 radical and N2O5 nocturnal chemical process is carried out, and the nighttime NOx removal mechanism is explored.

NO3自由基和N2O5是夜间对流层大气化学反应的关键物种，对于理解大气氧化性、二次有机气溶胶生成、NOx清除机制等对流层大气化学研究的关键问题具有非常重要的意义。由于它们活性高、寿命短、浓度低，大气NO3自由基和N2O5的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。.本项目拟开展城市大气NO3自由基和N2O5的外场观测研究。针对高颗粒物的大气环境，开展低损耗采样技术研究；探究进气损耗绝对定标方法，准确标定系统进气损耗；实现城市大气NO3 和N2O5的同步实时在线高灵敏准确探测。采用非稳态近似分析不同大气环境下NO3和N2O5的稳态寿命，探究NO3自由基夜间损耗机制，分析其对SOA生成的贡献；研究N2O5在气溶胶表面非均相沉降的摄取系数，分析硝酸盐、硫酸盐、湿度等因素与N2O5非均相反应的关系；揭示NO3自由基和N2O5的夜间大气化学过程，并进一步探究夜间NOx清除机制。

NO3自由基和N2O5是夜间对流层大气化学反应的关键物种，对于理解大气氧化性、二次有机气溶胶生成、NOx清除机制等对流层大气化学研究的关键问题具有非常重要的意义。由于它们活性高、寿命短、浓度低，大气NO3自由基和N2O5的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。突破了高颗粒物条件下的低损耗采样、光源与热高反腔的高效耦合、N2O5热解稳定性控制等关键难题，研制了腔衰荡探测系统（NO3/N2O5-CRDS），实现了NO3自由基和N2O5的同步高灵敏在线测量，探测限分别为0.8ppt（2.5s）和1.4ppt（2.5s），测量误差分别为8%、15%。解决了进气损耗标定难题，研究了进气损耗的整体定标方法，建立了整体标定系统，准确获得了NO3自由基和N2O5的进气损耗系数，实现了高颗粒物条件下NO3自由基和N2O5的准确探测。为了进一步探究测量准确性，开展了N2O5的综合外场测量对比（CRDS/CEAS）实验，两套系统具有很好的一致性，相关性系数R2为0.97，斜率为0.94。开展了综合外场观测实验，实现了夜间不同大气环境下（城市和城郊）NO3自由基和N2O5实时在线同步测量，分析了其浓度分布及变化特征；探究了夜间NO3自由基的氧化性及其对SOA生成的贡献，明确了N2O5气溶胶表面非均相反应的摄取系数及其影响因素，揭示了夜间硝酸盐形成的控制因素和NOx去除机制。.本项目的开展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，尤其对于认识我国区域性灰霾污染夜间形成机制具有重要作用。