基于CRDS系统对北京夜间大气边界层NO_3自由基观测与分析

夜间大气NO3自由基的氧化能力相当于白天OH自由基,鉴于NO3自由基在大气反应过程中的关键作用,准确测量其浓度及研究其夜间大气化学过程具有重大意义。采用以二极管激光器为光源(中心波长为662nm,半高宽0.3nm),两块高反射率镜片(R≥99.998 5%)形成的腔体为光学共振腔,有效光程达到约20km的腔衰荡光谱系统(CRDS)对夜间大气NO3自由基进行测量,并且针对秋冬季交通繁忙区域夜间大气边界层NO3自由基化学过程进行研究。采用该系统于2014年10月29日—11月15日在北京市中国科学院大学校园开展了NO3自由基连续外场观测实验,观测期间NO3自由基浓度相对较低,最大浓度约为50pptv,平均值为10pptv。并结合NO2,NO和O3等相关辅助数据对测量结果进行分析,分析表明在观测期间NO3自由基产率为0.04~1.03pptv·s-1,平均寿命约为68s。并且近一步分析了观测期间大气NO3自由基损耗途径,探讨了不同湿度及颗粒物浓度对其损耗的影响。即观测期间当大气中RH≥60%,PM2.5浓度大部分大于60μg·m-3时,ln(τss(NO3))与ln(NO2)的相关性达到0.79,大气中NO3自由基损耗主要以间接为主;然而在RH≤40%,PM2.5浓度大部分小于60μg·m-3时,因测量点靠近国道受局地污染源影响,直接损耗较显著;当大气中40%RH60%时,直接损耗与间接损耗途径都存在且不可忽视。

Nocturnal Atmospheric NO3 Radical Monitoring and Analysis in Beij ing with Cavity Ring Down System

The oxidizability of NO3 radical in the nocturnal atmosphere is comparable with that of diurnal OH radical.Given the importance of NO3 radical in the nocturnal chemical process,accurate measurement of its concentration and analysis its nocturnal chemical process have important significance.The article introduces cavity ring-down spectroscopy (CRDS)instrument which is applied to measure atmospheric NO3 radical.Light from a red laser diode (the wavelength is 662 nm and line width is 0.3 nm)is coupled on-axis into an optical cavity formed by a pair of high-reflectivity mirrors (R≥99.998 5%)to achieve an effective ab-sorption path length of approximately 20km.And it researches nocturnal chemical process of NO3 radical in view of the fall and winter heavy traffic areas.The measurement of NO3 radical with cavity ring-down spectroscopy was performed in Beijing from October 29 to November 15,2014.During the observation,the concentration of NO3 radical is relatively low with the maximum of NO3 radical concentration of 50pptv and the average of its concentration of approximately10 pptv.Combining of NO2 ,O3 and NO data,the observation results are analyzed.The NO3 production rates ranging from 0.04 to 1.03 pptv·s-1 were calculated throughout the observation,and NO3 lifetime averaged at 68 s.The NO3 loss process in the atmosphere is further analyzed. Combining of related auxiliary data,the influence of different humidity as well as particulate matter concentrates on the atmos-pheric NO3 removal is researched.When atmospheric RH≥60% and PM2.5 concentration mainly greater than 60μg·m-3 ,the correlation coefficient of the logarithmic correlation between NO3 lifetime and NO2 mixing ratio is 0.7 9 ,NO3 is mainly removed by the indirect loss process;however,when atmospheric RH≤40% and the concentration of PM2.5 mainly smaller than 60μg· m-3 ,because of the observation site is close to national highway and influenced by local pollution source,the direct loss process is main;When atmospheric 40%