| Pollution is one of the serious problems with the progress of industrialization. In recent years, because of the rapid increase of automobiles, the pollution of NOx has become a serious problem to the large cities in our country. Especially, the pollution of NOx will threaten people's health greatly. An atmosphere quality monitor network with appropriate distribution and rapid reaction in city area can ensure that the atmosphere pollution will be prevented and cured. Therefore, the Environmental Protection Agency of Guangzhou set up the project of "Research & Production of NOx Auto-Monitoring Analyzer for Atmosphere Quality". And we undertook this project and we had a lot of achievements.This paper is the sum-up of the design process and the achievements of NOi experimental analyzer. In the beginning, it briefly introduces some methods and principles of detecting NOx- And then, it emphasizes on the principles and the methods of chemiluminescence (CL) and it introduces the methods of converting NO? to NO in detail. In the second section, we deduced the formula for the linear relationship between the concentration of NO^ and power of the chemiluminescence by two ways and analyzed the influences on the efficiency of converting NOs to NO. The construction of Mo converter and its connection with other devices is explained in the third section. Also it introduces other devices in brief in this part, such as Reactor, Photo-Multiple Tube (PMT) and Ozonizer. In the fourth section, it expatiates the hardware and the software of the controlling circuit in this analyzer. In the last section, the paper states that the background signal has been reduced, after the system has been optimized, which makes it possible to improve the precision. And then, we respectively calibrated the analyzer with NO and NOi, which concentration is respectively 100PPM and 208PPM. Using these experimental data and the principles of chemiluminescence, we deduce the formula of computing the efficiency of converting NOa to NO. At last, the paper shows the results we got by the analyzer with which we measured the NOx in the air. And we found that the results are rational.The creative achievements shown in this paper are as follows:1. Optimize a new style Mo converter and do a lot of experiments about it, which shows a part of parameters of internal complicated construction and the relationship between the gas-circuit working parameters. The efficiency of converting NO2 to NO (87%) obtained from experiments, the best range of Mo working temperature (from 350 C to 370 C)and other properties of the NOx analyzer have not been found in any other articles.2. We realized that the background signal of O3 is intrinsic and stable.3. The best working parameters are that the ozone flow is 0.4LPM and the span flow is 0.8LPM. In these conditions the sensitivity of detection reaches the peak.4. When the counting time of PMT is 10 seconds, the ratio between the concentration of NO (PPB) and the counting rate (CPS) is 1:5.5. A series of parameters of NOx analyzer, including the temperature of reaction(50 C), converter(370 C) and PMT(5 C), the efficiency of the Mo converter(87%) and the ratio between the concentration of NOx (PPB) and the counting rate (CPS) (PPB:CPS=5:1) and so on, indicate that the PPB level NOx analyzer we are studying has entered into the period of turning it into applied instrument. |
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