Tracking Source Variations of Inhalation Cancer Risks and Ozone Formation Potential in Hong Kong over Two Decades (2000–2020) Using Toxic Air Pollutant Monitoring Data

Toxic air pollutants (TAPs) are a class of airborne chemicals known or suspected to cause serious health issues. This study, applying positive matrix factorization and inhalation unit risk estimates of TAPs, quantifies the changes in significant sources contributing to inhalation cancer risks (ICRs) from 2000 to 2020 in Hong Kong, China. Total ICR decreased from 1701 to 451 cases per million between 2000–2004 and 2016–2020, largely attributed to the reduction in diesel particulate matter (DPM), gasoline and solvent use-related volatile organic compounds (VOCs), and coal/biomass combustion-related polycyclic aromatic hydrocarbons and metal(loid)s. The regional contribution of VOCs associated with industrial and halogenated solvent sources increased substantially, representing the largest non-DPM ICR contributor (37%) in 2016–2020, stressing the need for a more comprehensive risk evaluation across the fast-growing and densely populated Greater Bay Area (GBA). ICRs in Hong Kong and the GBA will likely remain over 100 cases per million by 2050. The contributions to ozone formation potential of VOC/carbonyl sources were quantified, which show a notable shift from being solvent/gasoline-dominant in 2000–2004 to being more evenly shared by various sources in 2016–2020. Establishing a similar TAP monitoring network in the GBA is anticipated to provide the monitoring data needed to facilitate the development of more informed air quality management strategies.