| Summary: | 碩士 === 中山醫學大學 === 公共衛生學系碩士班 === 104 === This study examined the temporal and spatial variations of PM2.5 concentrations in Mailiao and Douliou, Yunlin, as well as the effects of synoptic weather types on the concentrations and compositions of PM2.5. Aerosols were collected in 11 sampling periods during 2013-2015. The compositions of aerosols, including water-soluble ionic components, EC, OC, and metals were then analyzed. In addition, hourly water-soluble ionic components were measured by an in situ IC system.
The transport/stagnant weather types are determined by hourly variations of the wind speed and direction, while 14 synoptic weather patterns were categorized by a weather chart. The stagnant weather conditions showed a higher probability of PM2.5 episode days (≥35μg/m3) occurring. The episode occurring percentage (episode days/total days, in each weather pattern) was the highest on type P3 (cold high-pressure system moving eastward to the Pacific Ocean with a center beyond 125°E longitude) among the 14 synoptic weather patterns. It was about 42% and 67% in Mailiao and Douliou, respectively.
The percentages of SNA (Sulfate, Nitrate, and Ammonium) in PM2.5 ranged from 29% to 43%, while the mean percentage of SNA in the stagnant weather type was higher than that in the transport weather type. Nitrate and ammonium concentrations were the highest for type P3, while sulfate concentration was the highest for P10 (prevailing southwesterly wind flows associated with the existence of a typhoon around South Korean Peninsula or Japan). The mean concentrations of PM2.5 for transport, stagnant, and P3 weather types were respectively 2.3, 3.0, and 4.0 times higher than those of the control group (PM2.5 < 20μg/m3 and temperature < 20°C). Compared to the control group, the increased levels of nitrate and ammonium were the highest on P3, while those of sulfate were highest on P10.
Variations of hourly water-soluble ionic components show that the daily maximum increase in levels of nitrate for the stagnant weather type was the highest among SNA. Results of excess ammonium (NH4+excess) indicated that higher values in the stagnant weather type were obtained than those for the transport weather type. Among the 14 synoptic weather patterns, the highest excess ammonium was found in type P3. In addition, when NR values of aerosol are lower than 0.7 (acid aerosol), the remaining nitrate ions (subtracting those combined with ammonium ions) combined mainly (65%) with sodium, while about 22% combined with calcium.
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