Variability and risk analysis of Hong Kong air quality based on Monsoon and El Niño conditions

This study presents an exploratory analysis aimed at improving understanding of the variability of Hong Kong air quality associated with different climate conditions. Significantly negative correlations were found when Niño 3 led particulate matter ⩽10 μm PM10) and NO2 by 2–3 months over the Hong Kong territory, while the other pollutants (e.g., O3, SO2) showed modest correlations. A significant decreasing trend in visibility was observed during the autumn and winter, which has potential implications for the air-quality degradation and the endangerment of human health in Hong Kong. In an El Niño summer, the visibility was relatively better, while visibility in other seasons was diminished. On the other hand, in La Niña events, significant changes occurred in visibility in winter and autumn. Air pollution indices were less sensitive to the South China Summer Monsoon (SCSM), but a relatively high correlation existed between the East Asian Winter Monsoon (EAWM) and air pollutants. Rainfall was lower during most of the strong EAWM years compared to the weak years. This result suggests that the pollutants that accumulate in Hong Kong are not easy to wash out, so concentrations remain at a higher level. Finally, based on the conditional Air Pollution Index (API) risk assessment, site-specific vulnerabilities were analyzed to facilitate the development of the air-quality warning systems in Hong Kong.