| dc.description.abstract | Taiwan is located to the southeast of the East Asian continent. In winter, the northeast monsoon can transport air pollutants from East Asian continent to Taiwan. Taiwan is surrounded by ocean; the effect of ocean is remarkable. Since the wind blowing, the sea-salt containing aerosols exist in atmosphere, and finally aerosols and pollutants deposit on ground via precipitation. The purpose of this study is to understand the long-term trends of precipitation chemistry and its correlation with regional climate pattern.
This study analyzes the rain water data collected from 2005 to 2013 at Taiwan acid rain monitoring sites. Pengjia Islet, Hsinwu and Chenggong are background stations, where the main source is ocean. The ratio of nss-SO42-/Na+ is lower than 1 at Pengjia Islet and Chenggong. In winter, the variability and seasonality in nss-SO42- is noticeable at Taipei, Yilan and Chungli. The ratio of nss-SO42-/NO3- is more than 1 at 6 stations which presents the relative importance of long-range transport.
The effect of transport depends on the strength of northeast monsoon, so higher Na+ concentration appears when northeast monsoon become stronger, while sea surface temperature (SST) is one of the factors determining the strength of northeast monsoon. It was found that the correlation between Na+ concentration and Niño 3.4 region SST is opposite in phase which indicates precipitation chemistry is indirectly affected by SST.
In order to further investigate the impact caused by northeast monsoon on precipitation chemistry, we choose the rain water data associated with the weather types NE (northeast monsoon) and FA (winter front). It shows that Hsinwu is close to sea so it is easy to affect by long-range transported pollution and the variability in nss-SO42- at Hsinwu is higher than Chungli. The variability in nss-SO42- at Chenggong is lower because Chenggong is not affected by northeast monsoon so significantly.
We analyzed the wind field and found extreme Na+ concentrations appear under the type NE at Pengjia Islet. The Na+ concentration maximum occurs when the wind speed over three days is larger than average. Meanwhile, the continental cold High still remains in continent so its intensity and wind speed are strong.
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