|Title:||The characteristics and source identification of airborne particles at the roadside of Hong Kong-PolyU (PU) supersite|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
Air -- Pollution -- China -- Hong Kong.
Automobiles -- Motors -- Exhaust gas -- China -- Hong Kong.
|Department:||Department of Civil and Structural Engineering|
|Pages:||xix, 311 leaves : ill. (some col.) ; 30 cm.|
|Abstract:||With the rising environmental and resultant health awareness, there are increasing concerns on particulate emissions due to the continuously growing vehicle numbers and kilometers driven in Hong Kong. Thus, investigation on particulate emissions related to vehicles is needed in order to improve urban air quality. This thesis is aimed to explore the characteristics and sources of airborne particles in ultrafine (Dp<0.1 um), fine (Dp<2.5 um), and coarse (2.5 um < Dp < 10 um) size ranges in the urban roadside environment. Investigation on the chemical compositions and abundance of aerosols shows distinct differences between ultrafine, fine and coarse particles at PU (PolyU) Supersite, a typical roadside site with heavy traffic. Aerosol mass and number concentrations are studied in different scenarios (daily cycles, large-scale weather systems and aerosol episodes). Distinct variations are shown on a daily basis in the number concentrations of ultrafine particles. In addition, high number concentrations of ultrafine particles are found in winter and low in summer. The diurnal cycles of fine particle mass concentrations track the fluctuations of the local vehicle numbers, on the other hand, the seasonal cycles are influenced by East Asia monsoons, which bring pollutants from upwind areas. For coarse particles, a good relationship is found between the hourly mean mass concentration and wind speed. The study of aerosol chemical compositions in each scenario indicates substantial variations for each fraction. Due to unfavorable synoptic systems, particulate episodes are observed in both summer and winter. The PSCF (Potential Source Contribution Function) receptor model identifies the coastal areas of southeastern China and the PRD (Pearl River Delta) region as the source areas of regional pollution in cold and warm seasons respectively. By analyzing the emissions from vehicles in the Shing Mun tunnel, a higher emission rate for diesel-fueled vehicle and unique chemical profiles for vehicles with different fuels are found. To better understand the sources of particles at PU Supersite, various techniques, including OC/EC ratios, linear/multilinear regression, PMF (Positive Matrix Factorization) and CMB (Chemical Mass Balance) receptor model, are applied in this study. Vehicle exhaust is identified as the major source for both ultrafine and fine particles, while resuspensions being the main source for coarse particles. Regional-scale pollution is another important source for fine particles. The contributions from regional pollution can increase to nearly half of the total fine particulate mass when air masses are from Mainland China.|
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