| 英文摘要 |
This study conducted an assigned mission of PM2.5 chemical speciation monitoring at Douliu, Chiayi, and Hualien air quality monitoring sites of Environmental Protection Administration for continuous eight days from the end of November to early December in 2016. In contrast, regular PM2.5 chemical speciation monitoring at Banqiao, Zongming, Douliu, Chiayi, Xiaogang, and Hualien were implemented on a shift of every 6 days starting from January to November in 2017. PM2.5 mass concentrations from these two types of collection varied consistently with those of continuous monitoring stations which indicated the achievement of representative collections of PM2.5.
PM2.5 daily averages, from January to November 2017, were 11, 20, 23, 28, 28, and 29 μg m-3, respectively, at the sites from east and north and south of Taiwan. Seasonal variations of PM2.5 mass concentration are with a pattern of the lowest in summer, higher than summer in autumn, and further up in winter and spring. In the winter time, the Xiaogang site was with the highest concentration due to bad environmental ventilation and the influence from upstream transport. In spring, the Douliu site ranked the highest but Chiayi was close to it especially for high concentration events. The Banqiao site became the highest in summer, while Xiaogang site claimed the highest in autumn. Volatilization and adsorption of PM2.5 chemical components were evaluated during collection. Underestimates of 6%~20% from NH4+, 4%~54% from NO3-, and 19%~62% from Cl- were found if only a single filter was installed for PM2.5 collection. Carbonaceous contents were with more negative interferences (volatilizations) in high PM2.5 mass concentrations in contrast to prominent positive interferences (adsorptions) in low PM2.5 mass concentrations. The highest levels of PM2.5 chemical component at each site for various seasons are as follows. In winter, SO4- was the highest chemical component at the Banqiao and Zongming sites, NO3- at the sites of Douliu, Chiayi and Xiaogang, and OC at the Hualien site, respectively. Whereas SO4- was the greatest component at the Banqiao, Zongming, and Hualien sites and NO3- at Douliu, Chiayi, and Xiaogang sites in spring. The OC was the highest component at the Banqiao and Zongming sites in contrast to SO4- at the other sites in summer. Interestingly, a unanimous highest SO4- level of chemical components was found for all sites in autumn. Splitting from daily average at 35 μg m-3, the ratio of NO3- to PM2.5 for low PM2.5 concentrations (17 μg m-3, n=266) relative to high PM2.5 concentrations (46 μg m-3, n=70) was elevated from 11% to 24% while other components shrank or unchanged. This indicates a need of stringent control of NOx emission sources, which is PM2.5 NO3- precursor. The highest two of PM2.5 metal elements are Na and K with the implication of the significant influences of sea-salt, fugitive crustal dust, and biomass burning. The computations of enrichment factor across all sites showed that fugitive crustal dust, coal combustion, and traffic emissions were important sources. Summarizing all events of PM2.5 concentrations greater than 35 μg m-3, this study found most events were under the influence of regional transport, bad ventilation, and photochemical reactions with only few from transboundary transport.
In summarizing PMF receptor modeling results for the 6 sites, the major pollution factors across all sites are derivative types of factor such as secondary nitrate and secondary sulfate. Secondary nitrate contributed high PM2.5 concentration ratios to most sites in spring and winter, while secondary sulfate contributed mostly in summer and autumn. The estimation of atmospheric visibility showed that corrected NH4+ or SO42- was the major PM2.5 chemical species influencing visibility at each individual site. This implies that the effects from derivative pollutants on atmospheric visibility are significant. For the assessment of PM2.5 chemical speciation techniques, 34 related international papers were collected and reviewed.
|