An Integral Spectroscopic Method For Measuring Concentration Of Nitrogen Dioxide Gas

Nitrogen dioxide is poisonous gas. The principle human-related sources of nitrogen dioxide are fuel combustion, industrial processes and vehicle exhaust in urban areas. Nitrogen dioxide can affect human health and is hazardous to vegetation. High concentration of nitrogen dioxide may contribute to formation of acid rain and photochemical smog. Environmental protection departments and law enforcement authorities have put great emphasis on the current situation of nitrogen dioxide pollution. Policy and laws have been released to control emissions of nitrogen dioxide to the atmosphere. The purpose of this study is to establish a method of monitoring nitrogen dioxide concentration featuring high precision, low cost and strong capabilities of anti-interference.The method of measuring the concentration of nitrogen dioxide was studied. This method is based on Beer-Lambert Law. A theoretical model for measuring the concentration of nitrogen dioxide called integral spectroscopic method was developed after analyzing the spectral properties of nitrogen dioxide gas, and software was created for data processing. Nitrogen dioxide gas measurement system was designed and built. The concentration of nitrogen dioxide gas could be automatically and continuously measured by the system, through program control. In spectral range of 400.96-474.57nm, the measurement is precise to 0.4ppm per meter with a detection limit of 1ppm per meter. The influence of spectrometer resolution variations on measurement of nitrogen dioxide was also studied. During the measurement process, the system had very strong anti-interference capability to changes in light intensity.Research on extending the effective optical path was carried out. In theory, based on the principle of integrating sphere, the proportion of photons which reflected different times to the total light in the integrating sphere was acquired, and the contribution of photon which reflected different times to average optical path was studied. For experiment part, nitrogen dioxide concentrations were measured by using integrating sphere and the effective optical path was expanded by 7.7-9.5 times. It was found that integrating sphere well coating reacted with nitrogen dioxide, and that nitrogen dioxide could be absorbed by integrating sphere well coating. The rapid decay of nitrogen dioxide was caused by both reasons.