Relationship of Visibility and Chemical Properties of Ambient Aerosols in Urban and Coastal Areas of Central Taiwan

Autor: Ying-I Tsai, 蔡瀛逸
Rok vydání: 1999
Druh dokumentu: 學位論文 ; thesis
Popis: 87
In this study, we investigate the past data of prevailing visibility and analyze the ambient aerosol components, scattering coefficient, and meteorological factors in Taichung urban and coastal areas from December 199 to January 1998 in order to interpret the degradation of visibility in central Taiwan. Prevailing visibility (Lv, km) and aerosol scattering coefficient (Ssp, km-1) in Taichung urban and coastal areas have a good inverse correlation. The relationships between prevailing visibility and scattering coefficient in the two areas areLV1= 2.82/(Ssp^0.81) and LV2= (3.71/Ssp^0.45), respectively, indicating prevailing visibility can be utilized for the study in relation of visibility and aerosol chemical property. Average concentrations of PM10 mass in urban and coastal areas are, respectively, 109.0+/-54.1 ug/m3 and 84.1+/-36.3 ug/m3. The dominant components in aerosols are carbonaceous materials, SO42- and NO3-, accounting for 55.8 % and 50.9 % of PM10 aerosols, respectively. The result reveals the anthropogenic pollution in urban area is worse than in coastal area. Visibility in urban and coastal areas reduces from 12 km and 16 km on clear days to only 4 km and 5 km on hazy days, respectively. In urban area during hazy days, the amounts of NO3- and organics in PM10 aerosols formed by atmospheric photo-oxidation reaction of traffic NOx emission significantly increase more than other chemical species. Comparing PM10 components on clear and hazy days in coastal area, the amount of SO42-, which is the product of atmospheric photo-oxidation reaction of SO2 originated from oil-burning and coal-fired emission, apparently increase on hazy days. During high-polluted periods, the weather environment usually situates high humidity and low wind speed. PM10 SO42-, NO3-, NH4+ and OC in the two areas highly correlate with O3 under humidity below 70 %, indicating there are strong photo-oxidation reaction and formation of secondary aerosols. Meanwhile, SO42- and NO3- have no significantly correlation with O3 under high humidity since the secondary aerosols had deliquesced. The amounts of aerosol mass and chemical species at dominant size range of 0.56-1.0 um in urban area are higher on hazy days than on clear days. In coastal area, the dominant peak of aerosol mass and chemical species shifts from the size range of 0.56-1.0 um on clear days to 1.0-1.8 um on hazy days and the amounts at this size range increase on hazy days. PM10 aerosols appear in neutral and alkalized forms on most days in urban and coastal areas, but particularly during episodes the aerosols contain more acidic properties, since the sulfur and nitrogen oxidation ratios (SOR and NOR) increase rapidly during smoggy days. The scattering coefficients of urban and coastal PM10 mass are 2.7+/-0.3 m2/g and 1.7+/-0.4 m2/g, respectively. Moreover, ammonia sulfate and elemental carbon are the most important contributors for scattering coefficient. In urban area, ammonia sulfate has the most significant scattering efficiency of 8.8 m2/g. Meanwhile, ammonia nitrate has the most significant scattering efficiency of 6.8 m2/g. Taichung urban atmosphere is influenced by secondary aerosols, marine sprays and road dusts. Secondary species and carbonaceous materials in PM10 at various wind speed significantly affect the urban visibility. In addition to secondary aerosols, marine sprays and road dusts, Taichung coastal atmosphere is also influenced by agricultural burning, oil-burning and coal-fired emission. The secondary aerosols with humidity increase apparently affect the coastal visibility. Moreover, the empirical models for Taichung urban and coastal visibility detect the variation of PM10 aerosol sulfate is the most sensitive to visibility change among all of the parameters, indicating that to decrease the urban and coastal aerosol sulfate formation can be helpful to local visibility improvement.
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