Abstract
Meteorological factors can result in air pollution. Some studies have indicated that the leeward side effect’s weak flow and subsidence play major roles in inducing high PM10 (particulate matter with a diameter of ≤ 10 µm) in southern Taiwan during winter due to topographic blocking. However, the results of this research showed that the rapid build-up of high PM10 in Kaohsiung city (KHC) during evenings is not completely explained by weak flow and subsidence. In northern Taiwan, topographic blocking on northwesterly enhances a significant pressure gradient force (PGF) induced strong winds. According to the Froude number (above 0.5), the flow in northern Taiwan can pass the terrain, producing subsidence warming in central Taiwan, which is located at the leeward side of the northeastern Central Mountain Range (CMR). In addition, strong winds blew river dusts in the middle of Taiwan under a stable atmosphere and stimulated density current, transporting PM10 to southern Taiwan. A large horizontal pressure gradient was still formed in central western Taiwan between the cold flow originating from northern Taiwan and the warm flow by subsidence warming. The strong PGF and the interaction between the flow and the terrain in northern Taiwan should favor the density current. After PM10 was transported into KHC efficiently in a short time by the density current, the local effect of weak rear flow and subsidence in KHC enhanced and maintained PM even more than it did in central Taiwan.
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