| dc.description.abstract | Recently, the China outflow and yellow-dust transport gained a lot of concerns globally. These pollutants and dusts moved by the weather system frequently influenced Taiwan air quality. In this study, aerosol observation was conducted at Shin-Men site, the northern tip of Taiwan, to investigate aerosol properties from long-range transport.
Aerosol concentration and SO2 were found elevated under the influence of cold continental high. In contrast, local emissions were dominant to result in low pollution level during non-cold-high period. The SO42- and NH4+ are dominant aerosol water-soluble ions and are higher than those in the time before and after the cold high event. Meanwhile, aerosol volatile organic carbon (OP) and low-temperature elemental carbon (EC1) were significantly increased in cold high event.
Among the four trajectory types, the transport along the China’s coast is with the highest aerosol level and the highest SO2/NOx ratio. The aerosols were distributed in 0.56-1.0 µm and 3.2-5.6 µm modes with SO42- and NH4+ as dominant aerosol water-soluble ions. The type of anti-cyclonic outflow is only less severe than the transport along the China’s coast in aerosol level and its aerosols are also distribution in 0.56-1.0 µm and 3.2-5.6 µm modes. The main difference between these two types is higher aerosol nitrate in anti-cyclonic outflow than the transport along the China’s coast. The local source contribution and oceanic transport are the two types with lower aerosol level. However, the ratio of PM2.5/PM10 is only 0.4 in oceanic transport as compared to 0.6 in local source contribution. In addition, the NOx concentration is the highest for local source contribution among all types. In aerosol carbon fractions, the second low-temperature elemental carbon (EC2) is the greatest in local source contribution among all types. The oceanic transport is featured with very low EC level but high organic fraction. The OP and EC1 are found significantly in the transport along the China’s coast. The anti-cyclonic outflow is with higher fractions in middle to high temperature OC.
The PM2.5 level in 2005 was found increased before the touch down of yellow dusts due to the contributions of industrial emissions forced by the frontal system. Coarse particles in the size range of 3.2-5.6 µm were significantly increased in contrast to the enhancement of 0.32-0.56µm and 0.56-1.0 µm in fine particles during the dust period. For the time periods when the dusts were significant, Ca2+, CO32-, and PM2.5-10 varied consistently which indicates that dusts are mainly in the coarse fraction and in the form of CaCO3. For aerosol carbons, the fraction of OC was decreased but EC1 was increased during the yellow-dust affected period. The most abundant low molecular-weight dicarboxylic acid was oxalic acid, which was slightly increased in the dust period. It indicates that oxalic acid could be in the air mass of the long-range transport.
For aerosol properties classified by trajectory types, the distinction was found for each type of aerosols both in concentration as well as in mass fraction. This demonstrates the usefulness of classification of aerosol properties by trajectory type. In addition, we can find that the influences of Asian-dust distinctly by classifying Asian-dust events into three periods. The compositions and the characterics of ratio in “non-yellow-dust” are different from “yellow-dust” obveriously. | en_US |