Variations of respirable suspended particulates in Hong Kong: cross-boundary and local effects

Abstract

Analysis of the spatial and temporal variability of respirable suspended particulates (RSP) observed in 11 Hong Kong general stations over the period 2000–2008 shows a high concentration in the northwest and low concentration in the southeast and coastal areas, with the central area in between. Seasonally, RSP concentration is highest in winter, followed by autumn, and is lowest in summer. A bimodal peak in diurnal cycle with peaks in the morning (7–8 a.m.) and early evening (6–7 p.m.) can be attributed to rush-hour traffic flows as well as local land–sea breeze circulations. The effect of vehicular emission is also demonstrated in a distinct weekly cycle, with a Sunday minimum. Analysis of RSP concentration for different wind directions shows the importance of cross-boundary transport of pollutants from the Pearl River Delta area, with 43% of noncompliant cases associated with cross-boundary transport. An empirical orthogonal function (EOF) analysis shows that the first EOF pattern of RSP changes is characterized by changes of the same sign for all 11 general stations, with the second pattern dominated by changes in the Yuen Long station. Time series analysis shows that changes in the second EOF leads the first, indicating that changes in Yuen Long (northwest) precede changes elsewhere. Stations located in the coastal area change last. Tap Mun shows significant increasing trends in RSP concentration, particularly for incidences of high RSP occurrences, which may be attributed to increases in shipping in the Yan Tian International Container Terminal. Raymond Kwok-Cheung Lok is currently affiliated with the HK Transport Department.