Castellanos Patricia, Luke Winston T, Kelley Paul, Stehr Jeffrey W, Ehrman Sheryl H, Dickerson Russell R
Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland 20742, USA.
Rev Sci Instrum. 2009 Nov;80(11):113107. doi: 10.1063/1.3244090.
Nitrogen dioxide (NO(2)) plays a central role in atmospheric chemistry, air pollution, and biogeochemical cycles. Many analytical techniques have been developed to detect NO(2), but only chemiluminescence-based instruments are commonly, commercially available. There remains a need for a fast, light, and simple method to directly measure NO(2). In this work we describe the modification and characterization of a small, commercially available cavity ring-down spectroscopy (CRDS) NO(2) detector suitable for surface and aircraft monitoring. A metal oxide scrubber was added to remove NO(2), and provide a chemical zero, improving the detection limit (3sigma of the background noise) from several parts per billion by volume (ppbv) to 0.06 ppbv, integrated over 60 s. Known interferences by water and particles were removed using Nafion tubing and a 1 microm Teflon filter, respectively. A 95% response time of 18+/-1 s was observed for a step change in concentration. The CRDS detector was run in parallel to an ozone chemiluminescence device with photolytic conversion of NO(2) to NO. The two instruments measured ambient air in suburban Maryland. A least-squares fit to the comparison data resulted a slope of 0.960+/-0.002 and R of 0.995, showing agreement within experimental uncertainty.
二氧化氮（NO₂）在大气化学、空气污染和生物地球化学循环中起着核心作用。已经开发了许多分析技术来检测NO₂，但只有基于化学发光的仪器在商业上普遍可用。仍然需要一种快速、轻便且简单的方法来直接测量NO₂。在这项工作中，我们描述了一种适用于地面和飞机监测的小型商用腔衰荡光谱（CRDS）NO₂探测器的改进和特性。添加了金属氧化物洗涤器以去除NO₂，并提供化学零点，将检测限（背景噪声的3σ）从体积分数十亿分之几（ppbv）提高到0.06 ppbv，积分时间为60秒。分别使用纳滤管和1微米的聚四氟乙烯过滤器去除已知的水和颗粒干扰。对于浓度的阶跃变化，观察到95%的响应时间为18±1秒。CRDS探测器与将NO₂光解转化为NO的臭氧化学发光装置并行运行。这两种仪器测量了马里兰州郊区的环境空气。对比较数据进行最小二乘拟合，得到斜率为0.960±0.002，R为0.995，表明在实验不确定度范围内具有一致性。
