Aerosol in the atmosphere and dry deposition in Hong Kong

香港的大氣及懸浮泣 [i.e. 粒] 子/沉積物的分析

Student thesis: Doctoral Thesis

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  • Ka Yee LEUNG


Awarding Institution
Award date14 Jul 2006


The study focused on the aerosol in Hong Kong. The sources and factors affecting the variations in concentrations of aerosol and dry deposition samples were of interest because less previous studies were performed in Hong Kong. Hourly data were collected from the Hong Kong Environmental Protection Department (HKEPD) in CD-ROM format. The PM10 concentrations of five monitoring stations were analyzed and statistical analysis was done to find out any differences among the averaged PM10 for each monitoring station. There was no significant difference of the PM10 among the five sites. The episode days with high levels of PM10 were identified and the effects of the synoptic weather systems on PM10 were investigated. It was found that high levels of pollutants were found when there was an approaching cyclone. The PM10 concentrations were correlated with the meteorological parameters and it was found that multivariate linear regression model can be used to deduce the amount of PM10. PM10 and PM2.5 collected at CityU were also compared. PM2.5 and PM10 showed strong correlation, implying that they came from the same source. The chemical composition of the aerosol was analyzed by capillary electrophoresis. The aerosol samples were collected by three kinds of sampling equipment: cascade impactor, TSP-high volume sampler and filter holders with Teflon membrane. The findings from the cascade impactor were used to find out the individual ion size distribution and its corresponding mass median aerodynamic diameter was determined. This parameter is important for the interpretation of the ion deposition velocity. The results from all three sampling equipment were compared with the ambient gaseous pollutant concentrations. It was found that nitrates were strongly correlated to the NO2 concentrations in the ambient air. The sulphate was also strongly correlated to the SO2 concentrations. The morphological features of aerosol particles were characterized by scanning electron microscopy with X-ray energy dispersive spectrometry. The particle dimensions for the particles collected were determined and the size distributions of the deposited particles were discussed. Furthermore, the types of particles were categorized into soot aggregates, minerals from land, marine mineral, marine-sulphate and nitrate, coal flying ash and other particles. The major elements found in the particles were Aluminium, Silicon, Calcium, and these elements originate from the crustal sources. Pure salt such as sodium chloride was also found. Sodium sulphate and sodium nitrate particles were identified and they were originated from the product of secondary aerosols (H2SO4, HNO3). The EDS spectra gave the detailed information regarding the atomic mass percentage for the existing element in the particle. Lastly, the dry deposition samples were collected and the chemical composition was analyzed by capillary electrophoresis. The use of different surrogate surfaces for collecting dry deposition (Polystyrene Petri dish, glass Petri dish and polystyrene Petri dish filled with Milli-Q water) was discussed. The dry deposition velocities for the major ions were determined by the dry deposition fluxes obtained and the mass concentration of the corresponding ion. Then the Slinn and Slinn model (1980) was used to find out the theoretical value of deposition velocities of the major ions and compare the results with the experimental results and the results calculated from a mixed modeling. The horizontal study of dry deposition fluxes at 18 sampling sites in Hong Kong was discussed and the results were analyzed by Cluster analysis. From the studies, it was found that the chloride depletion process was not dominant and most of the components of the aerosol and dry deposition originate crustal sources.

    Research areas

  • Hong Kong, Environmental aspects, China, Aerosols, Atmospheric deposition