| Summary: | 碩士 === 國立中央大學 === 環境工程研究所 === 104 === In this study, PM2.5 water-soluble inorganic ions (WSIIs) were monitored using an in-situ Particle-Into-Liquid-Sampler coupled to an Ion Chromatograph (PILS-IC) system at Lulin Atmospheric Background Station (LABS, 2,862 m a.s.l.) in spring 2015. Meanwhile, PM2.5 and PM10 mass concentrations, PM1 and PM10 light-scattering and -absorption coefficients, trace gas concentrations, and dynamic variations of aerosol number concentrations and size spectra monitored at LABS were also adopted for discussion.
PM2.5 mass concentraions were averaged at 3.2±0.3 μg m-3 during the period without been affected by the transported biosmass burning (BB) smoke, upslope wind, and fog event. Among PM2.5 chemical components, anion dominated WSIIs with SO42- averaged at 0.7±0.1 μg m-3 as the predominant component in contrast to relative low concentration of cation with NH4+ incapable of complete neutralizing SO42- and NO3-. Meanwhile, LABS was frequently affected by the upslope wind accompanying with the rises of CO, O3, RH, PM10, and PM2.5. Three cloud events happened in the afternoon to result in the rises of pollutant levels by having the mean values of CO, O3, and PM2.5 at 0.13±0.04 ppm, 48.3±9.4 ppbv, and 16.5±4.1 μg m-3, respectively, and that of SO42-, NH4+, and NO3- at 3.6±0.8, 2.2±1.1, and 1.5±0.8 μg m-3, respectively. The values of Dissolved Gas over Measured Ions (DIGMI) were calculated by dividing the dissolved SO42- concentrations in fog droplets in equilibrium with atmospheric SO2 over SO42- measured by PILS-IC. The DIGMI values were frequently greater than 1 before the occurrence of a cloud event in contrast to less than 1 during and after a cloud event. It indicated that SO42- was transported by the upslope wind from the hill to reduce the DIGMI values in the cloud events.
Durning the four BB events (including upslope and cloud events), mean levels of CO, O3, PM2.5, K+, SO42-, NH4+, and NO3- were 0.26±0.3 ppm, 74.2±7.9 ppbv, 28.8±6.7 μg m-3, 0.6±0.1 μg m-3, 4.1±0.8 μg m-3、3.0±1.0 μg m-3、1.9±0.4 μg m-3, respectively. In most occasions, excess NH4+ (ExNH4+) was found enough to complete neutralizing SO42- to form (NH4)2SO4 and (NH4)2SO4. The DIGMI values were often less than 1 with a mean value of 0.71±0.16 during the fog peroid when influenced by the transported BB smoke. This implied that SO42- in the transported smoke was more than that of the dissolved SO2 in the fog droplets.
Take mean values of NH4+, K+, NO3-, and SO42- during the time period not affected by the transported BB smoke, upslope wind, and fog events as the base case for comparing with that of the other time periods in terms of percentage differences are shown as follows. For the period not affected by the transported BB smoke but under the influence of the upslope wind, the differences for NH4+, K+, NO3-, and SO42- were 98.7%, 57.4%, 88.8%, and 40.8%, respectively. Similarly, the differences for the period not affected by the transported BB smoke but under the influence of fog events were 100.0%, 83.6%, 98.6%, and 68.8%, respectively. Moreover, the differences of NH4+, K+, NO3-, and SO42- for the period affected purely by the transported BB smoke were 100.0%, 96.6%, 98.8%, and 69.2%, respectively. In the case for the period affected by the transported BB smoke and upslope wind, the differences of the aforementioned WSIIs were 100.0%, 96.6%, 98.8%, and 77.0%, respectively. Finally, the differences of the precedent WSIIs were 100.0%, 96.1%, 99.1%, and 74.6%, respectively, for the period affected by the transported BB smoke and fog events.
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