Hourly PM2.5 extremes variation in conjunction with meteorology in urban Hong Kong

Atmospheric aerosol particles with diameters of less than 2.5 mm (PM2.5) have significant health effects on both human and various ecosystems. With increasing traffic and energy consumption, PM2.5 has become the main type of air pollutant in Hong Kong, and extreme concentrations of PM2.5 appear to occur more frequently. This paper investigates the variations in the extreme hourly PM2.5 concentrations from the Air Pollution Index (API) monitoring station in Central - Hong Kong, which represents a typical urban area of Hong Kong. The hourly PM2.5 concentration exhibits the distinct seasonal and diurnal variations, which were impacted by traffic strength and meteorological conditions. The analysis results reveal that firstly, significant diurnal bimodal pattern of PM2.5 with peaks in morning (8:00-10:00am) and afternoon rush hours (18:00-20:00pm) are noted, lowest concentrations are generally found around noon time (12:00-14:00pm). Secondly, seasonal variations of PM2.5 concentrations with their highest concentration during winter and lowest during summer times, which are driven by seasonal variability in wind directions and temperatures. Thirdly, the pronounced variations are commonly contributed to anthropogenic factors, such as enhanced traffic density, yet meteorological conditions also have some significant influence in Hong Kong.