請用此 Handle URI 來引用此文件: http://hdl.handle.net/11455/5679
標題: 台灣中部都會及沿海地區能見度與大氣氣膠化學特性關係之研究
Relationship of Visibility and Chemical Properties of Ambient Aerosols in Urban and Coastal Areas of Central Taiwan
作者: 蔡瀛逸
Tsai, Ying-I
關鍵字: 能見度
大氣氣膠
化學組成
出版社: 環境工程學系
摘要: 本研究以能見度歷史資料及1996年12月至1998年1月之台中都會與沿海地區的大氣氣膠成分、散光係數及氣象參數,探討兩地能見度不佳之原因。 台中都會及沿海地區之盛行能見度(Lv, km)與氣膠散光係數(Ssp, km-1),具良好負相關,都會及沿海地區之兩者關係分別為LV1= 2.82/(Ssp^0.81)及LV2= (3.71/Ssp^0.45),顯示盛行能見度可運用在能見度與氣膠特性關係之研究上。 都會地區PM10 mass為109.0+/-54.1 ug/m3,沿海地區則為84.1+/-36.3 ug/m3,兩地區之氣膠成分均以碳粒、SO42-及NO3-為主,其組成在都會及沿海地區,各佔PM10 mass之55.8 %及50.9 %,顯示都會地區之人為污染較沿海地區嚴重。 在高污染狀態,都會及沿海地區之能見度,分別由良好空氣品質之12 km及16 km降至僅4 km及5 km,在都會地區之氣膠組成,尤以交通排放,經光化反應所形成之NO3-及Organics,增加特別明顯。沿海地區之氣膠,在高污染時,以鍋爐燃燒或燃煤電廠之污染排放,經光化反應形成的SO42-,更是顯著增加。 高污染時期,大氣多處在高濕度且擴散不易的低風速狀態。以相對濕度RH 70 %作分界,在RH<70 %,兩地PM10 SO42-、NO3-、NH4+及OC與O3呈現高度正相關,顯示低濕度下,有強烈O3光化反應,二次氣膠生成。而高濕度狀態,SO42-、NO3-等二次氣膠已潮解,與O3之關連性較低。 都會地區在高污染事件發生時,0.56-1.0 um之微粒所佔質量粒徑分率,明顯高於良好空氣品質狀態。沿海地區在高污染狀態之粒徑分率,從良好空氣品質之0.56-1.0 um粒徑範圍,略增為1.0-1.8 um之粒徑區間,其區間濃度明顯增加。兩地PM10氣膠,平均呈現中性偏鹼性之特性,但在高污染狀況下,PM10之硫轉化強度(SOR)及氮轉化強度(NOR)快速增加,其氣膠轉變成酸性。 都會及沿海地區之PM10 mass的散光效率分別為2.7+/-0.3 m2/g及1.7+/-0.4 m2/g,硫酸銨及元素碳,乃是造成散光係數上升之主要原因,其氣膠物種之散光效率,在都會地區以PM10硫酸銨最高,達8.8 m2/g,沿海地區之PM10氣膠物種,以硝酸銨的散光效率最高,其效率為6.8 m2/g。 都會地區大氣受到二次氣膠、海水飛沫及塵土之影響,其能見度在不同風速下,二次氣膠及含碳物質之影響明顯。而沿海地區之大氣,尚受農廢燃燒、燃煤或重油燃燒之污染排放影響,而能見度受到濕度變化而成長之二次氣膠影響較大。此外,台中都會及沿海地區能見度之經驗模式,均以硫酸鹽對能見度變化最具敏感性,顯示降低都會及沿海地區之氣膠SO42-之生成,可進而改善能見度。
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.
URI: http://hdl.handle.net/11455/5679
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