Characterization of toxic air pollutants in Hong Kong, China: Two-decadal trends and health risk assessments

Exposure to toxic air pollutants (TAPs) is linked to the development of cancer and various chronic health issues. While studies on the ambient characteristics of criteria air pollutants such as particulate matter, nitrogen oxides, and ozone have been extensively conducted, research on TAPs in China remains limited. In particular, there has been a lack of long-term observation studies on the potential health risks associated with ambient TAP concentrations. To address this gap, we characterize the long-term trends (2000-2020) of a wide range of TAPs in Hong Kong using ambient monitoring data derived from a TAP monitoring program that has been in operation since the late 1990s. We analyzed TAPs such as diesel particulate matter (DPM), volatile organic compounds, carbonyl compounds, polycyclic aromatic hydrocarbons, hexavalent chromium, and others. We found that most of the TAPs decreased notably over the last two decades, translating to a reduction in economic loss of over HK$2 billion per year in 2016-2020. However, the current state of TAPs still poses significant health risks. The total TAP concentrations in 2016-2020 exceeded the chronic reference guideline value for noncancer health hazard quotient of 1.0 (1.53). The aggregated inhalation cancer risks in the corresponding period were 562.8 in a million population. We found that the top ten TAPs disproportionately accounted for more than 80% of both health estimators. In contrast to earlier years where DPM dominated the cancer risks, the measured VOCs have grown in importance, and they pose cancer risks as significant as DPM in recent years. Our work identifies several areas in enhancing TAP monitoring, which have implications for expanding the monitoring across the Greater Bay Area for improving air quality management from a health-oriented perspective.