A Nitrogen Dioxide Detector for the Clean Troposphere

这个小型企业创新研究第一阶段项目将开发一种检测对流层中二氧化氮(NO2)的方法，二氧化氮是对流层中氮氧化物(NOY)的最重要成分之一。直接测量NO2对于了解决定对流层臭氧自然水平的化学过程以及评估人类影响排放的潜在影响至关重要。直接测量未受污染的对流层中的NO2的困难来自于低浓度(100pptv)以及其他更丰富的氮化合物的潜在干扰。这项提议将开发一种直接光谱方法，利用可调谐半导体激光光源的红外吸收，直接探测清洁对流层中NO2的绝对水平。拟议研究计划的一个关键组成部分是开发一种长路径、低体积的吸收池，该吸收池具有足够的长度(600M)以提供足够的灵敏度，同时具有最小的体积(10升)以实现快速采样和最短的仪器响应时间。在细胞入口处对痕量物种的调制将允许实时背景减去以进一步提高灵敏度。对已知谱线参数进行曲线拟合的自动信号处理将提供绝对浓度水平，而无需使用校准气体。由此产生的仪器将具有4ppt的二氧化氮检测下限和100%的S信号平均时间。

This Small Business Innovation Research Phase I project will develop a method for detecting nitrogen dioxide (NO2), one of the most important components of nitrogen oxide species (NOy) in the troposphere. Direct measurements of NO2 are crucial for understanding the chemical processes that determine natural levels of tropospheric ozone and for assessing potential effects of human-influenced emissions. The difficulties associated with direct measurements of NO2 in the unpolluted troposphere arise from low ((100 pptv) concentrations and the potential for interferences from other more abundant nitrogen compounds. This proposal would develop a direct spectroscopic method using infrared absorption with a tunable diode laser light source which would directly detect absolute levels of NO2 in the clean troposphere. A key component of the proposed research plan is the development of a long path length, low volume absorption cell which would have sufficient length ( 600 M) to provide adequate sensitivity and yet have a minimal volume ((10 liters) to enable rapid sampling and a minimal instrument response time. Modulation of the trace species at the cell inlet would allow real-time background subtraction to further increase the sensitivity. Automated signal processing using curve fitting to known spectral line parameters would provide absolute concentration levels without using calibration gasses. The resulting instrument would have an NO2 detection limit of 4 ppt with a signal averaging time of 100 s.