Fine particulate matter events associated with synoptic weather patterns, long-range transport paths and mixing height in the Taipei Basin, Taiwan

Abstract

Asian dust storms (ADS) and PM2.5 (particle pollution) events have an evident influence on air quality in Taiwan. However, the synoptic weather patterns and atmospheric conditions on ADS days are not entirely similar to those related to PM2.5 event days. The aim of this study is to clarify the weather characteristics such as synoptic weather patterns, long-range transport paths, and stagnant conditions that precipitate PM2.5 events. Air quality and meteorological data from 2006 to 2013 were obtained from government-owned observation stations, and the mixing height was estimated in relation to the Nozaki planetary boundary layer height. This study used back trajectories as simulated gridded analysis data, which were based on kinematic trajectory analysis using NASA's GMAO (Global Modeling Assimilation Office) and NCEP (National Centers for Environmental Prediction) analyses. For testing the differences between means of two large, independent samples, the confidence interval of a common statistical indicator was employed. The results show that in comparison to low PM2.5 level days, weather features such as stagnant conditions, including low mixing height and low wind speed, low rainfall amount, and high solar hours, are favorable for inducing PM2.5 events. Eighty percent of the synoptic weather patterns on PM2.5 days were associated with either polar continental high pressure, a high-pressure system in mainland China moving from the continent to the sea, or a stationary front stretching from southern China to the East Sea, and moving eastwards. More than 81% of the contributing factors of the causes of PM2.5 events were found to be related to stagnant conditions. The pattern of the contributing factors causing the maximum-recorded concentration of PM2.5, (73.90 μg/m3) was attributed to local emissions, and a long-range transport time that was extended for a longer period over the land than over the sea. The synoptic weather patterns were also found to affect the spatial distribution of PM2.5 concentrations in the basin.