|dc.description.abstract||Atmospheric fine particulate matter (aerodynamic diameter less than or equal to PM2.5) will pose human health risk and cause atmospheric environmental change. In order to understand PM2.5 variation trends in Northern, Middle, and Southern Taiwan, this study summarized the results of PM2.5 mass and chemical components manually collected at Xinzhuang, Banqiao, Chungming, Qianzhen, Qianjin, and Siaogang, respectively from 2011 to 2015. The correctness of aerosol components is affected by volatilization of semi-volatile species and the adsorption of volatile organic gases during PM2.5 collection. In this study, a three-filter series was adopted to correct the interference of volatile species and affecting factors. Source apportionment of PM2.5 was conducted by using Positive Matrix Factorization (PMF) with the assistance of Conditional Probability Function (CPF) for local source evaluations. In the final step, the effects of meteorological factors and polluted sources were regressed on ambient visibility.
The results show that PM2.5 mass level was highest in March and SO42- was a predominant species in all seasons in Northern Taiwan. However, the corrected organic carbon (OC) competed with SO42- as the predominant component in summer which indicated organic compounds were important in summer. PM2.5 mass level is highest in autumn and SO42- is a predominant species in all seasons in Middle Taiwan. In addition, PM2.5 mass level is highest in winter and SO42- is a predominant species in all seasons in Southern Taiwan.
The volatilization of NO3- and Cl- are significant as the volatile ratio is greater than one in most occasions. The fraction of NO3- to PM2.5 mass level increased from 6% to 13% when PM2.5 mass level was low (<35μg m-3) as compared to high (>35μg m-3). In implies that the reduction of NO3- and Cl- precursor sources will help reduce high pollution events. Meanwhile, NH3(g) was found to penetrate from denuder adsorption as the equivalence of volatile NH4+ was greater than the equivalence of volatile (NO3-+Cl-) most of the time.
The fractions of volatile OC to retained OC level in the first filter were 9%, 11, and 8% in Northern, Middle, and Southern Taiwan, respectively. Moreover, the fractions of adsorbed volatile organic gases to retained OC level were 18, 16%, and 14% in Northern, Middle, and Southern Taiwan, respectively. If no correction was made, the OC fractions in retained OC mass level would overestimate 9%, 5%, and 6%, respectively. The volatilized NO3- and NH4+ are related to maximum ambient temperature and corrected PM2.5 mass level; however, the volatilized Cl- is not significantly affected by maximum ambient temperature.
The source apportionment using PMF and aided by using CPF showed that sources of secondary sulfate, nitrate, and chloride contributed greatly in Northern, Middle, and Southern Taiwan. It indicates fossil fuel combustion is the most significant source in affecting urban PM2.5 air quality. The degradation of atmospheric visibility is most serious in Southern Taiwan with visibility averaged at 7.5±3.16 km. In contrast, the visibilities in Northern and Middle Taiwan are better with values at 12.57±4.13 km and 12.72±3.4 km, respectively. From multiple regression analysis on ambient visibility by using PM2.5 chemical components, pollution sources, and meteorological factors, water-soluble inorganic ions and meteorological factors are found significant in affecting the visibility in Northern, Middle, and Southern Taiwan.