Seven sets of samples that were taken from sites upwind and downwind of Hong Kong during the summer and winter seasons were analyzed. The solvent extractable organic compounds (SEOC) were separated into four major fractions (n-alkanes, fatty acids, alkanols and (polycyclic aromatic hydrocarbons (PAHs)) and identified using gas chromatography-mass spectrometry (GC-MS). Five different wind directions were detected during the two seasons: southwest, southeast, east, east-northeast and northeast. At one extreme, the southwest wind brought clean aerosols from the South China Sea to Hong Kong, diluting the urban aerosols, and the anthropogenic contribution was found to be fresh and local. At the other extreme, when the northeast wind prevailed, there was a significant increase (10-14 times) in the total SEOC yield and the characteristics of the aerosols indicated a greater impact from outside Hong Kong (i.e., more PAHs, plant wax contribution, and lower C18:1/C18:0 ratios), suggesting the presence of aged aerosols. In the samples taken during prevailing east-northeast winds in November, the loading was low and bore resemblance to the summer samples. In addition, there were changes in the characteristics of the aerosols, such as an increased plant wax contribution in the fatty acid and alkanol fractions, signifying a change in season. The characteristics and loading of the PM2.5 at the downwind site were found to be significantly influenced by the accumulation of locally emitted air pollutants due to no wind conditions and the transport of long-distance (from surrounding regions) and short-distance (within Hong Kong) plumes.
Continuous measurements of aerosol number size distributions from 3 nm to 10 mum have been first performed within the city area of Beijing since March 2004. Size distributions of the first 45 measurement days (March 05 to April 18, 2004) were investigated in terms of their high variability. Two dust storm events were observed indicated by high number concentrations greater than 1 mum and mass concentrations around 1 mg m(-3). Continental highly polluted air was observed during 12 days indicated by a number peak in the accumulation mode range, and submicrometer volume concentrations above 150 mum 3 cm(-3) were observed. Newly formed particles with more than 100,000 cm(-3) were observed on 25 days when the particle surface area concentration drops below a critical value (100-2000 mum 2 cm(-3)) because of clean air from the north. Measurements show only a slight growth (similar to1 nm h(-1)) of the particles indicating that they are produced within the city area of Beijing.