Influences of natural and anthropogenic particles on ambient particulate air quality during typhoon season: From Bashi Channel to Kaoping River Valley

摘要

Aeolian dust episode (ADE) is an emerging disaster occurred from the bare lands of the Kaoping River Valley in southern Taiwan because of typhoons. Four manual sampling sites located along the Kaoping River Valley conducted to collect PM_(10) (aerodynamic diameter ≤ 10 μm) with high‐volume samplers during the ADE occurred by Typhoon Doksuri, and on regular days. Mass percentages of sea‐salt particles (SSs) in PM_(10) accounted for 5.47–8.91% on regular days and 11.66–14.05% in phase II. Average mass percentage of Ca~(2+) in phase I increased twice than those on regular days. Cl~(?) deficit percentages were much lower during the ADE (7.37–14.13%) than on regular days (31.69–42.78%), indicating acidic particles mainly produced by chemical reactions of acidic aerosols with aeolian dust and SSs. Even alkaline aeolian dust is a dominant source of the ADE, the atmospheric particles are attributable to acidic particles in the air. Hence, anthropogenic sources play a key role for the worst air quality during typhoon season. In this present study, four PM_(10) manual sampling sites (MS1, MS2, MS3, and MS4) were employed at the potential area of aeolian dust in the middle stream of Kaoping River valley since the ADE was difficult to predict in southern Taiwan after Typhoon Morakot in 2009. In addition, the meteorological data were recorded by ambient air quality monitoring stations (Linyuan [LY], Daliao [DL], Pingtung [PT], and Meinong [MN]) stations established by Taiwan Environmental Protection Administration (Taiwan EPA) along the Kaoping River valley. While the Typhoon Doksuri passed through Bashi Channel on June 29, 2012, its anticyclone outflow circulation entered into the estuary of the Kaoping River. Since the Kaoping River flows southwards, huge amounts of accumulated fine sands on the surface of Kaoping River were blown by the airflow and then suspending in the air for several hours at least. According to the meteorological data recorded by four Taiwan EPA's automatic monitoring stations (LY, DL, PT, and MN) during the ADE, southern winds were dominant at the downstream of Kaoping River. The wind directions at MN station were obviously distinguished from the others. Thus, the blowing aeolian dust was restricted by the topography of the Kaoping River valley.