The relationship between typhoon features and fine particulate matter: events in Metropolitan Taipei

The fine particulate matter (PM2.5) events occurring in a basin, where the subsidence of local emissions outside the periphery of a typhoon is coupled with pollutants transported by the horizontal airflow, threaten public health. The hourly concentrations of PM2.5 in metropolitan Taipei, Taiwan, from 2006 to 2016 were obtained for 17 sites from the Environmental Protection Administration. Hourly meteorological data were obtained for 29 sites from the Central Weather Bureau. The life stages of each of the 60 alerted typhoons studied were divided into seven time periods. The data were analysed using the z statistics and t tests, as well as Duncan's multi-range test and back-trajectory tracks. The main aims of this study are (1) to determine the relationships between the PM2.5 concentrations in the Taipei Basin and the life stage, strength and event rate in the position (ERP) of an alerted typhoon and (2) to determine the relationship between the PM2.5 events and long-range transport during the typhoon period. The results show that in comparison to the PM2.5 events, conditions such as the strength of weak and tropical depression in the typhoons and the life stages of not in the affected scope of the storm were of greater importance for the occurrence of serious PM2.5 events. Furthermore, in relation to the PM2.5 events, the typhoons were further from Taipei when the serious PM2.5 events occurred. Multiple factors like terrain blocking, sea breeze, poor air dispersion due to subsidence and long-range transport could induce a PM2.5 event or serious PM2.5 event.