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A case study for the NO_x photolytic convertor and its application in the field campaign

摘要：将一套基于NO₂光解原理自主设计的光解室与Thermo 42i系列氮氧化物分析仪的化学发光检测室联用,应用于四川资阳乡村站的外场观测中.结果发现,在进样流量170 mL·min^-1、光源温度20℃、光源功率约60 W的条件下,该套自主设计的光解室对NO₂的转化效率可连续30 d稳定在80%.同时,与传统钼转化炉法进行了比对,发现两种方法得到的NO浓度测量结果趋于一致(误差5%以内,R²=0.99);而NO₂的测量结果则是钼转化炉法显著偏高于光解法,偏差约为3.72 ppbv(R²=0.86).将两种方法的测量差值(ΔNO₂)与O₃、NO_z([NO_z]=[NO_y]-[NO_x])及NO₂光解速率J(NO₂)等数据进行分析,推论出ΔNO₂由钼转化炉中部分NO_z热转化所致,且ΔNO₂在NO₂低浓度段偏差的不确定性也初步归因于NO_z浓度测量的不确定性.利用观测中获得的HONO、HNO₃、PAN浓度代表NO_z对NO₂进行修正后,再次与光解法测量结果比对,结果证实钼转化炉法的高估值确由部分NO_z物种导致,同时证实光解法测量结果更接近NO₂的真实值.

Abstract：A set of photolytic convertor based on the principle of nitrogen dioxide photolysis reaction was coupled with a chemiluminescence detector(Model 42i-TL NO-NO₂-NO_x, Thermo Fisher Scientific Inc.)and tested in a field campaign at rural site of Ziyang, Sichuan. Under the conditions of 170 mL·min^-1 injection flow rate, 20℃ light source temperature and 60 W source power, a high and stable conversion efficiency of NO₂ was obtained (more than 80% up to 30 days). The photolytic convertor was compared with the molybdenum convertor from December 2012 to January 2013. A good consistence was found in NO concentrations (error within 5%,R²=0.99), while the NO₂ measurement results by the photolytic convertor was about 3.72 ppbv (R²=0.86) lower. By subtracting concentrations of the main NO_z components(e.g. HONO、HNO₃、PAN)from that of NO₂ by the molybdenum convertor, we can further confirm that the NO₂ measurement results by the photolytic convertor was closer to the actual values.