Impact of motor vehicles on roadside air quality in Hong Kong

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Impact of motor vehicles on roadside air quality in Hong Kong

 

Author: Cheng, Kwan Yuen
Title: Impact of motor vehicles on roadside air quality in Hong Kong
Degree: M.Sc.
Year: 2012
Subject: Air -- Pollution -- China -- Hong Kong.
Motor vehicles -- Environmental aspects -- China -- Hong Kong.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Civil and Environmental Engineering
Pages: 56 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2551490
URI: http://theses.lib.polyu.edu.hk/handle/200/6875
Abstract: According to the statistics done by Hong Kong Government, roadside air pollution had been the problem for a long time. Among the pollutants, nitrogen dioxide (NO₂) was believed the rapidest rise. The major reason have been found out that is related to the exhaust after-treatment devices retrofit program. The installation of diesel oxidation catalyst (DOC) leads to the increment of f-NO2, based on the oxidation process done on NO which emits from the diesel engine. Other reasons of increasing roadside NO2 are because the high level of ozone causes NO to NO₂ and the increase in total fuel consumption of vehicles. Besides DOC, selective catalytic reduction (SCR) and exhaust gas recirculation (EGR) had also been installed in some diesel vehicles. However, they have been investigated that there are some disadvantages on each of them. SCR has only the highest efficiency (undergo fast SCR reaction) when the NO/NO₂ ratio is equal to 1:1, while the ratio from diesel exhaust is 9:1 which can only undergo NO₂SCR reaction which got lower conversion rate than fast SCR. And EGR is hard to control because of the varying operation conditions within diesel engine. Also, the range of temperature is another consideration for the improvement. NOx HyCat is introduced to solve the problem, with its combination of the conventional SCR (CSCR), it is able to operate at a wide range of temperature. And there is a new catalyst indeed which is cerium-manganese oxide. This is used to convert the 9:1 NO/NO₂ ratio to optimum 1:1 so as to activate the highest efficiency, fast SCR reaction afterwards. Also, for the policies recommendation, government should not only restricting the standard since it may meaningless if there is no new invention, but strengthening the inspection and maintenance program with introducing PEMS also. Lastly, "to replace rather than to retrofit" is recommended to provide a better environment.

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