Abstract

This study conducted a cluster analysis on the fine particulate matter (PM2.5) data over Taiwan from 2006 to 2015 and diagnosed their association with the synoptic weather patterns. Five clusters are identified via a hierarchical clustering algorithm; three of them correspond to severe events, each with a distinct pattern of temporal evolution within the 240-h window. The occurrence of the different clusters exhibits strong seasonal variation. Two of the polluted clusters are more frequently associated with weak synoptic weather, while the other one is related to northeasterly winds and fronts. Detailed case studies show that the weather patterns’ temporal evolutions clearly modulate the transition among various pollution clusters by influencing the changes in local circulation and atmospheric stability. In winter, the clusters characterizing severe PM2.5 pollution events occur when Taiwan is influenced by persistent weak synoptic condition, while in autumn, the long-range transport by strong northerly winds leads to the occurrence of severe PM2.5 pollution. The current results shed light on the potential of combining the data-driven approach and the numerical weather forecasting model to provide extended range forecasts of local air pollution forecasts.

Highlights

  • Pollution of fine particulate matter with a diameter smaller than 2.5 microns (PM2.5 ) is a crucial environmental and public health issue in Taiwan, and the influence of the weather systems on PM2.5 pollution has been studied extensively

  • We further examined the number of extreme events with the Air Pollution (API) values exceeding 60%, which is the threshold of the 99th percentile in the API data

  • We applied the hourly PM2.5 concentration data observed at 73 Taiwan EPA ground stations from 2006 through 2015 to develop an air pollution indicator that depicts the overall state of air pollution within a spell over Taiwan island

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Summary

Introduction

Pollution of fine particulate matter with a diameter smaller than 2.5 microns (PM2.5 ) is a crucial environmental and public health issue in Taiwan, and the influence of the weather systems on PM2.5 pollution has been studied extensively. The PM2.5 concentrations are contributed by both local emission sources and long-range transport, and the severe PM2.5 pollution conditions often occur from autumn to the following spring [2,3]. The regional environmental conditions, such as temperature, humidity, atmospheric stability, boundary layer features, and local circulation affected by terrain, could influence the transport and accumulations of pollutants (e.g., [6]). Over the East Asia monsoon region, the above regional ambient conditions are mainly modulated by different types of synoptic weather systems seasonally [7].

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