The objective of this project is to (1) investigate the relationship between the weather conditions and the air pollution problem; (2) support the daily air quality forecast; (3) propose the air quality forecast operation strategy. The result of the classification identified six weather types. Cluster 1, 2 and 3 (C1-C3) are typical winter weather types and appears from October to next March, and are associated with high air pollutants concentrations. C3 is affected by a weak synoptic weather pattern and associated with the lowest wind speed and the highest PM2.5, PM10 and O3 concentrations. C3 is also the most prevalence weather type that is prone for the occurrence of the PM2.5 event. C4 occurs mostly during the season transitional month and is associated with high O3 concentrations. C5 and C6 are summer weather types and with low air pollutant concentrations. Analysis of the 39-year ERA-interim reanalysis dataset (1979–2017) reveals a weakening of East Asia winter monsoons, a reduction in the northeasterly monsoonal flow, and an overall stably stratified atmospheric structure from surface to 300-hPa level in the Taiwan area. The observed surface wind speed also appears to be in a long-term decline. Attempts to reduce high PM2.5 concentrations are the least effective in Western Taiwan from the central to southern parts, situated on the leeside of a mountain range, where stagnant wind conditions and strong subsidence are often exhibited.

Synoptic weather pattern, PM2.5, O3, long-term trend analysis