Development of Automated and Continuous Measurement Equipment for Air Pollution Gases by Using Miniature Diffusion Scrubber and LED Photometer

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In recent years, air environment pollution has become a big problem. While various analytical instruments have been used for the measurement of air pollution gases, but it is not convenient for the on-site analysis. Because analytical instruments are expensive and need to be set in a laboratory. Therefore, the simple and convenient equipment is required for measuring air pollution gases.In this study, we developed "miniature diffusion scrubber", which became more compact in size. This devise is very simple structure as a double tube, and it can efficiently collect only gases. This device uses PPTFE (porous poly tetra fluoro ethylene) tube for the inside tube and a poly-carbonate tube for the outside tube. The miniature diffusion scrubber can collect pollution gases into only 1ml of trapping solution. Therefore, colorimetric method with LED-PM (Light Emitting Diode-Photometer) can determined these gases without a concentration process.The concentration of formaldehyde and nitrogen dioxide in ambient air were actually measured by this equipment and the conventional method. It showed a good agreement between the measured values by both methods.Next, we developed a new automated continuous measurement system of air pollution gases. This system consists of the miniature diffusion scrubber and LED-PM. A trapping solution feeds into the PPTFE tube and an air is drawn into the annular space between the PPTFE tube and the glass tube. The PPTFE tube also acts as an absorption cell. The absorbance of trapping solution inside the scrubber can be measured in parallel with air sampling. The LED for the light source can also work as a wavelength selective photodetector.We compared nitrogen dioxide and oxidants concentrations in ambient air measured by this equipment with those measured by conventional methods. The concentrations of nitrogen dioxide and oxidants in ambient air measured by both methods showed a good agreement, respectively, during the same period.