請用此 Handle URI 來引用此文件: http://hdl.handle.net/11455/5496
標題: 大氣中硝酸氣體採樣誤差及多環芳香族化合物(PAHs)健康風險評估之研究
Study of Sampling Artifacts for Measurement of Nitric Acid Gas by Annular Denuder System and Health Risk Impact of Ambient Air Polycyclic Aromatic Hydrocarbons (PAHs)
作者: 張冠甫
Chang, Kuan-Foo
關鍵字: Nitric acid
硝酸
annular denuder system
sampling artifact
particles
PAHs
size distribution
nano-particle
環型擴散採樣器
採樣誤差
微粒
多環芳香族化合物
粒徑分布
奈米微粒
出版社: 環境工程學系
摘要: 本研究主要分為兩大部分,分別為第一部分:利用環型擴散採樣器(annular denuder system, ADS)採集大氣中硝酸氣體採樣誤差之研究以及第二部分:大氣環境中多環芳香族化合物(polycyclic aromatic hydrocarbon, PAH)之特性分析與健康風險評估之研究。第一部分主要是以數值模式以及實際大氣採樣方式來推估硝酸氣體採樣時所受到採樣誤差之影響。第二部分為大氣中多環芳香族化合物之粒徑分布、濃度特性以及利用毒性等值因子(toxicology equivalency factor, TEF)將所分析之21種多環芳香族化合物轉換為等值benzo(a)pyrene(BaP)之濃度,以了解到不同採樣點間所受到大氣中PAH之影響。 在利用數學模式模擬環型擴散採樣器採集大氣中硝酸氣體時結果發現,溫度越高、入流微粒數目濃度越大、微粒粒徑越大、小於2.5 m微粒中硝酸根離子之濃度越高以及入流硝酸氣體濃度越小時,會有較多之相對誤差產生。因此,未來在類似大氣環境下採樣時應注意到採樣誤差的產生。 本研究同時利用四根串聯塗覆相同NaCl吸附劑之環型擴散採樣器採樣管組裝方式來推估採樣誤差之情形,結果發現,採樣過程中,會有採樣正誤差以及負誤差同時發生在採樣管中。同時,正負誤差可以相互被抵銷,而導致採樣總誤差發生。採樣負誤差在硝酸氣體濃度較低以及採樣溫度較高時有較高之誤差值產生。而採樣正誤差主要會受到微粒中硝酸根離子濃度以及大氣中含氮氣體之影響。 由於模式模擬值以及實際大氣採樣所推估之總採樣誤差值之間仍有一段差距,因此本研究推估,在採樣過程中也會受到大氣中其餘含氮氣體(N-containing gas)之影響,如NOx、PAN以及HNO2等等。研究結果顯示,採樣過程中微粒揮發、擴散以及含氮氣體所造成之誤差百分比分別為77、9以及14 %。由研究結果中發現,微粒的揮發作用是採樣誤差的主要來源。而影響微粒揮發作用的主要因子,則是微粒中硝酸根離子濃度及大氣中硝酸濃度。 大氣中固相21種PAH的濃度值在工業區、都會區以及郊區分別為102.4、93.4以及81.3 g/m3。而氣相21種PAH的濃度在工業區、都會區以及郊區分別為1530、1030以及758 ng/m3。2-4環PAH在氣相中佔絕大部分,約為95 %以上,相反的在固相PAH中分子量較大之PAH所佔之比例較大,約為50 %左右。 在BaP毒性等值因子的研究方面,氣相PAH的毒性等值因子在工業區、都會區以及郊區分別為118、115以及75.3 ng/m3。而在固相PAH中,毒性等值因子則為4.24、8.97以及4.56 ng/m3。氣相PAH的毒性可以用BaP來作為代表,而固相PAH的毒性則可以利用DBA來作為代表性之PAH。此結果顯示,台中地區受到氣相PAH之影響較固相PAH為嚴重。 本研究利用MOUDI採樣器以及PS-1採樣器來估計大氣中之粒徑分布,同時配合Noll and Fang模式來推估大氣微粒之乾沉降速度。結果顯示,工業區之微粒乾沉降量為最高,都會區次之,郊區最低。同時,PAH的乾沉降量在工業區、都會區以及郊區之乾沉降量分別為58.5、48.8以及38.6 ug/m2/day。
This study contains two major parts. Part 1 focused on the sampling artifacts of nitric acid gas by using annular denuder system (ADS). A theoretical model was developed in this part to evaluate the theoretical sampling artifact. Four denuder tubes coated with the same NaCl adsorption in an annular denuder system was also applied in the field experiment to evaluate the positive and negative errors. Part 2 concentrated on the characteristic (including gaseous and particulate concentrations and size distribution) of ambient air polycyclic aromatic hydrocarbon (PAH) and its health risk assessment in different sampling sites of central Taiwan. The result of theoretical model indicated that the sampling artifact of nitric acid gas was more serious under situation of higher ambient temperature, higher inlet particle number concentration, larger inlet particle diameter, higher nitrate concentration in diameter less than 2.5 m particle and lower inlet nitric acid gas concentration. Field study was conducted to evaluate degrees of positive and negative errors as well as possible error sources of one NaCl-denuder system for HNO3 measurement. The results indicated that both negative error and positive error could simultaneously exist, but they might cancel each other and lead to less remarkable overall error concentrations. The negative errors could be important for sampling relatively low HNO3 concentrations or at high ambient temperatures. On the other hand, the positive errors could be due to both N-containing gases and nitrate particles. This study also intended to quantitatively determine the contribution of positive error from either particle phase (evaporation error and diffusion error) or gas phase (N-gas error). The result indicated that the evaporation, diffusion and N-gas error was 77 %, 9 % and 14 %, respectively to the total positive error. The nitrate concentration in less than 2.5 m particles and the true HNO3 gas concentration were the key factors that influence the degree of evaporation error. High values of these two factors could cause significant error concentrations and must be avoided in the field measurement of atmospheric HNO3 gas by a denuder system. The particulate total PAH concentration was 93.4, 81.3 and 102.4 ng/m3 in the urban, rural and industrial sampling site, respectively. The gaseous total PAH concentration was 1030, 758 and 1530 ng/m3 in the urban, rural and industrial sampling site, respectively. The result indicated that the influence of gaseous PAH was more serious than the particulate PAH in central Taiwan. 2-4 rings PAH contributed about 95 % of total gaseous PAH and medium molecular weight PAH (5-6 rings) occupied about 50 % in the total particulate PAH. The gaseous PAHs in central Taiwan carcinogenic activity can be explained by individual BaP concentration because it is high percentage of carcinogenicity to the total carcinogenic activity. The 21 particle-bound PAHs concentrations were 118, 75.3 and 115 ng/m3 for industrial, rural and urban, respectively. For carcinogenic activity of particle-bound PAHs, the BaP equivalent concentrations were 4.24, 8.97 and 4.56 ng/m3 for industrial, rural and urban, respectively.
URI: http://hdl.handle.net/11455/5496
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