|Author:||Cheung, Tsz-fai Vincent|
|Title:||Measurement of atmospheric hydrocarbons and air quality in Hong Kong|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Hydrocarbons -- China -- Hong Kong -- Measurement
Air quality -- China -- Hong Kong
Air -- Pollution -- China -- Hong Kong -- Measurement
|Department:||Department of Applied Biology and Chemical Technology|
|Pages:||viii, 149 leaves : ill. (some col.) ; 30 cm|
|Abstract:||A dedicated air sampling and gas chromatographic analysis system was built to measure parts-per-trillion (pptV) to parts-per-billion (ppbV) levels of non-methane hydrocarbons (NMHCs) at a coastal rural background air monitoring station in Hong Kong. The accuracy of analysis was successfully validated by inter-laboratory comparison of calibrated NMHC standards and ambient air samples provided by Dr. D.R. Blake, Department of Chemistry, University of California (Irvine), U.S.A. C2-C6 non-methane hydrocarbons (NMHCs) were measured at the Hong Kong Polytechnic University Regional Air Monitoring Station for the period October, 1995 to March, 1997 on a near daily basis. The annual total C2-C6 NMHC concentrations showed a clear high-winter and low-summer seasonal variation trends, though pollution episode days due to influence of micro-meteorological conditions were occasionally observed throughout the year. Monthly averages of total C2-C6 NMHC concentrations were in the range of 10 - 50 ppbC (on per carbon basis), with alkanes accounting for 60% of the total concentration, which are typical of the NMHC levels reported for rural/non-urban environments with emissions originating from anthropogenic sources. The seasonal variation of NMHCs is attributed to the dominant influence of outflow of Asian continental air masses in the winter, and inflow of Pacific maritime air masses in the summer. The origin of air masses reaching Hong Kong was analyzed and classified by 10-day back trajectory calculations. Relatively high levels of measured NMHCs, characterized by a higher % acetylene content, were associated with continental air masses encountered in Hong Kong. The winter NMHC concentrations show very good linear correlations (r2 > 0.8) with acetylene and CO, suggesting that fossil fuel combustion and biomass burning are a major contributory sources of NMHC pollution derived from the outflow of Asian continental air masses. Good linear correlations (r2 > 0.8) were also found between signature NMHC species derived from liquefied petroleum gas (LPG), suggesting the co-occurrence of LPG leakage as another NMHC contributory source. In summer, the NMHC levels were much lower than that in the winter and showed no clear or very weak correlation among NMHC species of known anthropogenic sources. This was supported by back trajectory analysis that maritime air masses from South and West Pacific Ocean could reach Hong Kong in the summer months. Thus the composition of C2-C6 NMHCs may serve as signature fingerprints of Pacific maritime air masses encountered in Hong Kong. At the monitoring site, the measured NMHC levels in some occasions could be strongly influenced by the changes in local meteorological conditions. More than 10 folds increase in total NMHC concentration was observed on local episode days when surface winds were sweeping urban pollutants direct onto the air monitoring station. During cold front days in the winter, the measured total NMHC levels were increased by 2 folds due to the greater anthropogenic emission loading in the continental air masses. The chemical composition and characteristics of the continental air masses vary with time of the cold front period. The surface wind speed increased to 14 m/s or higher, contribution from photochemical "less aged" air masses, as indicated by the highest % content of reactive species like propylene and ethylene, were observable in the associated NMHC measurements. Our data set is in quantitative agreement with the findings of the NASA Pacific Exploratory Missions (PEM-West A & B) which also observed higher NMHC levels during the late winter and early spring, and lower NMHC levels in the summer and early autumn. The PEM-West A & B studies were aircraft-based measurements with flight path stretching a large part of Western Pacific (north to Japan, and south to Singapore and Indonesia), but only of limited time span. In contrast, our data set is more comprehensive in providing information on meteorological, micro-meteorological, estimation of emission sources and time span effects on pollution levels at Hong Kong and its neighboring regions.|
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