dc.description.abstract | Atmospheric fine particulate matter (with aerodynamic diameter less than or equal to 2.5 μm, PM2.5) have a great impact on both the environment and human health. PM2.5 mass concentration and chemical composition vary significantly in different times and places. To understand PM2.5 temporal and spatial variations systematically, aerosol samples collected at various places in a fixed time interval is preferred. This study collected 41 PM2.5 mass concentrations at the eight air quality monitoring stations of Taiwan Environmental Protection Administration (TEPA) and resolved PM2.5 chemical composition at the Xinzhuang, Chungming, and Siaogang stations from March 9 to November 16, 2011. The aim of this study is to investigate PM2.5 mass concentration and chemical composition in Taiwan metropolitan area. The subjects studied include deviations between manual collection and continuous monitoring, the conversion of PM2.5 from continuous monitoring to manual collection, field and trip blanks analysis, the artifact corrections from adsorbed gases and semi-volatilized particles, mass closure for analyzed and modeled aerosol components, source apportionment for urban aerosol, derivation for potential compound forms, and factors affecting urban haze and visibility.
The results show that temporal variation of PM2.5 from R&P 2000 federal reference method (FRM) is consistent with continuous monitoring at the eight air quality stations. The coefficient of determination (R2) from linear regression for the whole data could reach at 0.87. However, most R&P 2000 FRM PM2.5 concentration are lower than that of continuous monitoring with an average of absolute deviation at 32%. By contrast, the manual collection of PM2.5 from R&P 2300 and R&P 2000 are correlated well with an R2 value at 0.87 and an average of absolute deviation at 21%. The deviations of PM2.5 mass concentration between two manual collectors are affected by honeycomb denuders and filter package installed in R&P2300.
Blank analysis for chemical composition reveals that field blanks for carbonaceous content and the water-soluble ions in the second and the third filters frequently exceeded two times of method detection limit. SO42- was the major chemical component of PM2.5 at the three speciation sites in spring and fall. By contrast, organic carbon (OC) was the major chemical component in summer. The volatilized percentage of NO3- was lower in spring but higher in summer and fall although the volatilized concentration was not high. The volatilized NO3- and NH4+ concentrations can be estimated with the highest R2 at 0.84 by the collected PM2.5 mass concentration and the highest ambient temperature during collection. Absolute Principal Component Analysis showed that PM2.5 was mainly contributed by photochemical pollution followed by gasoline vehicle emissions. Aerosol water content occupied a considerable fraction of aerosol mass even under 35% RH from mass closure assessment and model simulation. For aerosol compound forms, (NH4)2SO4(S) and NH4NO3(S) were derived for spring and summer; while (NH4)2SO4(S), NH4NO3(S), and NH4Cl(S) were reasoned for fall. Multiple regression analysis (MRA) for atmospheric visibility showed that NO3- and SO42- were major PM2.5 components at the Xinzhuang and Siaogang stations and NH4+ and Cl- were significant at the Chungming station. Among the environmental factors, relative humidity was selected as a significant factor for visibility impairment in MRA. For the haze event during observation period, aerosol components and gaseous pollutants were significantly increased with the increase of NO3-. This indicates vehicle emissions were mainly responsible for haze event. The major chemical species affecting the visibility at the Siaogang station were NO3- and NH4+ during haze event period.
In the present study, PM2.5 mass concentration and composition were investigated systematically to obtain PM2.5 geographical and seasonal variations. In addition, the relationship between manual measurement and continuous monitoring was established and volatilization of semi-volatiled species was evaluated. Finally, source apportionment for PM2.5 and factors affecting visibility degradation were resolved.
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