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Air Quality Part 5

Tham khảo tài liệu 'air quality part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Methods for online monitoring of air pollution concentration 93 Fig. 7. SO2 monitoring device schematic according UV fluorescence principle Baumbach 1997 . 3.3 Chemiluminescence Chemiluminescence is related to UV fluorescence. The difference between the two is that in chemiluminescence molecules are not excited by UV radiation but are excited by a chemical reaction. Thus the measuring principle is a chemo-physical one. The intensity of the radiation created is a measure for the concentration of the reacting gas in a mixture of gases if the external conditions pressure temperature and volume flow of the measuring gas are kept constant. Just as is the case in UV fluorescence the radiation created is recorded by a photomultiplier acting as radiation detector and is transformed into an electric signal. This method is used mainly for measuring NO NO NO2 i.e. NOx and O3. To measure the NO and NO2 concentration into the atmosphere the TUV EU and U.S. EPA requirements are fulfilled only by chemiluminescence s method. The instrument must provide continuous and unattended monitoring of NO NO2 and NOx with individual determinations and high reliability and accuracy. An internal NO2 to NO converter permit NOx analysis and an integral ozone supply system which puts filtered dehumidified ambient air through an ozonator to generate the ozone necessary for reaction with NO to give chemiluminescence s reaction. The instrument must have a flow-chopping modulation system to give continuous NOx and NO analysis. With this system the sample gas is divided into two separate lines. One sample gas line passes through the N02 to NO 94 Air Quality converter while the other leads directly to the detector. Also a permeation tube in which only moisture is passed through is used for the sample line is needed. This tube functions so that an influence from the moisture is reduced by minimizing difference of moisture concentration between sample gas and reference gas. Inside the reaction chamber NO