Non-methane hydrocarbon characteristics of motor vehicular emissions in the Pearl River Delta region

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Non-methane hydrocarbon characteristics of motor vehicular emissions in the Pearl River Delta region

 

Author: Tsai, Wai-yan
Title: Non-methane hydrocarbon characteristics of motor vehicular emissions in the Pearl River Delta region
Degree: Ph.D.
Year: 2007
Subject: Hong Kong Polytechnic University -- Dissertations.
Automobiles -- Motors -- Exhaust gas.
Air -- Pollution -- China -- Pearl River Delta.
Department: Dept. of Civil and Structural Engineering
Pages: xiv, 205 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2116718
URI: http://theses.lib.polyu.edu.hk/handle/200/2371
Abstract: Air pollution problem in Hong Kong and the Pearl River Delta (PRD) region has raised much concern from the public in recent years. The primary aim of this research is to use field measurement data to characterize non-methane hydrocarbons (NMHCs) in emission from motor vehicles. Fuel vapor compositions for several commonly used vehicular fuels in Hong Kong, Macau, Guangzhou and Zhuhai were analyzed in 2003, and they are believed to be the first one reported for the PRD region. These profiles were used to study the impact of evaporative loss of the fuels on air quality. High toluene contents were found in the gasoline fuel vapors in Hong Kong and Macau, and the values were much higher than those reported in other countries such as the US and Canada. The benzene contents in gasoline used in Hong Kong and Macau were strictly controlled below 1%, but the contents in Guangzhou and Zhuhai were 3 to 6 times higher due to their looser regulations, and it affected the benzene emission in auto-exhaust in these cities. Roadside samplings were conducted from 2000 to 2003 in the four cities mentioned above. The results showed that in all the four targeted cities, vehicular engine combustion was a main NMHC source, while gasoline evaporative losses also contributed much to the total NMHC. Vehicles in Guangzhou and Zhuhai were found having higher degrees of gasoline evaporative losses and we proposed this to be the result of poorer car maintenance and more old cars in these two cities. From the tunnel measurements conducted, evaporative loss of gasoline was responsible for the high i-pentane and toluene concentrations in all tunnel atmospheres; LPG leakage was also found to be significant from the measurement data collected in Hong Kong. Characteristics of vehicular engine exhaust emissions were studied in Hong Kong, Guangzhou and Zhuhai. Measurements of diesel emission before and after the introduction of low sulfur diesel in the Guangdong Province in 2004 showed a large influence on the emission profile due to the change of diesel compositions. The E/E ratios implied that gasoline-powered vehicles in Hong Kong were equipped with well functioning catalysts, while those in Guangzhou and Zhuhai, especially the motorcycles, were found dirtier in NMHC emission. Although the E/E ratios showed that private cars in Hong Kong had high combustion efficiency, the existence of significant amounts of unburned gasoline in their exhaust stream pointed out that they still had low fuel economy. From the results of a simple model, it was found that the evaporative losses of gasoline and LPG contributed much to the total NMHC pollution from vehicle. Gasoline-powered vehicles accounted to around 40% of total vehicle fleet, but gasoline evaporative losses already accounted to half of the total NMHC emission inside the tunnel, with another 15% contributions from engine combustion of gasoline-powered vehicles. The preliminary results from the dynamometer study conducted in Hong Kong showed large variations of exhaust characteristics for private cars and taxis during different driving speeds. Aromatics hydrocarbons (mainly toluene) were found to be the most dominant hydrocarbon class for potential ozone formation in private car emissions; while unburned LPG components were the major contributors for the potential ozone formation in taxi emissions. The results can be used as scientific basis for regulatory parties in designing standards and strategies to improve the air quality in this region, and will certainly add substantially to the scientific database for the international community.

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