Study of ambient halocarbons in Hong Kong: temporal variability and implication on source origins

Halocarbons have been recognized for their role as major ozone-depleting substances (ODSs) since the 1970s, and some also function as greenhouse gases (GHGs). International agreements, such as the Montreal Protocol, Kyoto Protocol, and Paris Agreement, were established for worldwide cooperation to gradually reduce the production and use of halocarbons. Initial success was achieved in phasing out global chlorofluorocarbon (CFC) production, but recent studies found an unexpected decrease in the rate of decline in the atmospheric concentration of trichlorofluoromethane (CFC-11) after 2012.

Historically, halocarbons have been emitted from various anthropogenic sources (e.g., the dry cleaning industry, electronic industry, and refrigeration) in Hong Kong. Emission sources in the Pearl River Delta (PRD) region, such as chemical manufacturing, also have remarkable impacts on the ambient halocarbons in Hong Kong. The ambient mixing ratios of major CFCs were declining in Hong Kong and the PRD region before 2010. However, no continuous measurements of ambient halocarbons were conducted in Hong Kong after 2010. Given that CFC emissions from the PRD region account for up to 25% of their total emissions in China, any unexpected CFC emissions in recent years will have significant impacts on the atmospheric abundance of halocarbons worldwide.

We have been continuously monitoring ambient halocarbons in Hong Kong since Fall 2020. The temporal variability of major halocarbons and their source origins have been extensively investigated using multiple approaches. Our results indicate lower enhancements beyond the background values for major regulated CFCs and CCl₄ than later controlled HCFCs and HFCs, suggesting the greater progress of Montreal Protocol implementation for the former species. The notable high enhancement values of non-regulated halocarbons from the north direction indicate their widespread usage in China. This work provides insight into the progress made in implementing the Montreal Protocol in Hong Kong and the surrounding region and the importance of continuous emission control.