| 英文摘要 |
To understand the formation mechanism of fine particulate matters (PM2.5) and control them, this study reviews relevant papers and reports and investigates the trends in air pollutants by using Fourier decomposition and generalized site-specific trend model.
Literature review indicates that sulfate, ammonium, nitrate, and organic carbon (OC) constitute the major parts of PM2.5. The composition varies from site to site. The concentration of ammonium and nitrate in urban areas is higher than those in rural areas. The observation of nitrate concentration, also varying with the level of photochemical reaction, reveals the difference of concentrations between northern and southern Taiwan. The annual concentration of non-sea salt sulfate increased from 2002 to 2005, but no significant changes of other species were observed. Seasonal variation shows that nitrate constitutes less in summer but higher in winter and spring. In summer, high peak of sea salt sulfate of PM2.5 is observed in Taiwan, except Pingtung. EC concentration has no significant seasonal variation, but OC does. The highest ration of OC is observed in summer. The ratios of ammonium to sulfate in equivalent are greater than 2 in all reviewed literatures, indicating the existence in (NH4)2SO4. However, the ratios of ammonium to (2*sulfate+nitrate) in equivalent are less than one, except for Yun-Chia-Nan and Kao-Ping air basins. Sulfur oxidation rate (SOR) increases from southern toward northern Taiwan. The SOR in all air basins, except Yilan, are larger than 0.25, indicating that strong sulfur oxidation occurs and may result from long-range transportation. Though nitrogen oxidation rate (NOR) in Kao-Ping air basin is less than 0.1, the NOR in North, Central, and Yun-Chia-Nan are larger than 0.1, revealing nitrates transfer from local pollutants and may be produced by long-range transformation or transportation.
Fourier decomposition and generalized site-specific trend models are utilized to investigate the annul trends of PM2.5. The two approaches indicate similar results: the decrease in the concentration of PM2.5, PM10, NOx, and SO2 in almost every air basins, especially an enormous decrease in the north air basin.
MM5 and Models-3/CMAQ are used to simulate the meteorological and air quality, respectively. The results of both simulations pass the requirements of evaluation guidelines for model performance. The fractions of primary, secondary components, and water in fine particles are 35.2%, 31.3%, and 33.5%, respectively. The major source for primary component is crustal element and the major species for secondary fine particles are sulfate, nitrate, and ammonium. Note that the results for organic carbon are not consistent with simulation results and literature reviews. The contributions from point, line, and area sources in each air basins to sulfate, nitrate, and ammonium of fine particles are studies by using CMAQ-TSSA. The results show that the major sources for sulfate are from the point sources, and the line source in the north air basin is also a significant source for sulfate. The sources for nitrate are generally from the line source in each air basin itself, except for Chu-Miao and Yun-Chia-Nan air basins, in western Taiwan area. The sources of ammonium are all from area sources in each air basin itself, with contribution greater than 50% for each air basin itself and greater than 80% for combination with upwind air basin.
The effect of control measures in Taiwan is evaluated by the analysis of the relationship between air pollution emissions and ambient air quality. Primary PM2.5 emissions in line sources decrease largely from 2005 to 2011, while emissions from point sources increase slightly. The annual variation of primary PM2.5 emissions from point, line, and area sources vary by 0.25％, -3.31％, and -1.59％, respectively. The annual variation of line source SO2 emission decreases (-14.8%) largely, while there are slight decreases with emission categories of point and area sources (-1.21% and -0.17%, respectively). Since the line source SO2 counts little (2%) in total emissions, the total SO2 annual variation decreases slightly. The decreasing trend of line source NOx annual variation is consistent with the trend of line source SO2. The annual variation of SO2 from point, line, and area sources are -0.14％, -4.19％, and -0.71％, respectively. The decrease of NMHC emission from point and line sources is observed by -3.83% and -3.57%, while NMHC from area sources increases by +1.32%. In summary, variation of all emissions from every source decrease from 2005 to 2011, except for primary PM2.5 from point sources and NMHC from area sources.
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