Volatile organic compounds (VOCs) are high volatility gaseous organic compounds across multiple chemical classes, typically in trace concentrations. VOCs and their photochemical reaction product ozone (O₃) in the troposphere can lead to health and environmental impacts. Despite the decreasing VOCs and NO_x in Hong Kong, increasing O₃ was observed. Under a VOC-limited regime, Hong Kong warrants further VOC studies. In addition, some halocarbons are ozone-depleting compounds that contributed to the ozone hole, while others serve as source tracers. Alkyl nitrates (RONO₂) can be emitted or photochemically formed and are reservoirs of reactive nitrogen. Hence, both groups were also measured in this study. To explore the temporospatial VOC concentration and composition variations, its O₃ forma...[ Read more ]

Volatile organic compounds (VOCs) are high volatility gaseous organic compounds across multiple chemical classes, typically in trace concentrations. VOCs and their photochemical reaction product ozone (O₃) in the troposphere can lead to health and environmental impacts. Despite the decreasing VOCs and NO_x in Hong Kong, increasing O₃ was observed. Under a VOC-limited regime, Hong Kong warrants further VOC studies. In addition, some halocarbons are ozone-depleting compounds that contributed to the ozone hole, while others serve as source tracers. Alkyl nitrates (RONO₂) can be emitted or photochemically formed and are reservoirs of reactive nitrogen. Hence, both groups were also measured in this study. To explore the temporospatial VOC concentration and composition variations, its O₃ formation potential, and the impact of regional transport, 587 and 35 whole air canister samples were collected in HKUST and at sea to quantify 86 VOCs via GC-FID/ECD/MSD. The analysis results showed seven C_1-4 VOCs contributing to 62.2% total average concentration in HKUST. Alkanes contributed to the highest concentration portion (> 50%). Thus, its seasonal and diurnal variations governed total concentration variations. Despite the lower concentrations, alkenes and aromatics yielded higher ozone formation potential (OFP) than alkanes. Isoprene was the primary contributor towards concentration and OFP fluctuations of alkenes. In contrast, opposite seasonal variation patterns were observed for aromatics. Benzene, toluene, ethylbenzene, and xylenes (BTEX) saw the highest concentration and OFP enhancement in December, with solvent usage as the major source in HKUST. The remaining C_8-9 aromatics exhibited the opposite pattern, except styrene. Further investigation of toluene-to-benzene ratio (T/B) indicated complex source contributions in September and consistent vehicular emission in December. Seven correlated spikes of CFC-11, CFC-113, and methyl chloroform were observed in HKUST (Rp > 0.6). Solvent usage was the likely source, as indicated by the simultaneous enhancements of tracers TEX. Furthermore, enhancement of halon and CFC-113 in marine samples implied potential emissions from seaborne vessels. In contrast, bromoform was the sole halocarbon primarily contributed by oceanic emission. Overall, most samples yielded air mass age below 24 hours, indicating an origin within the Pearl River Delta. The highest air mass age and variations were observed in September, while December exhibited the lowest. Marine samples in polluted days yielded lower air mass age alongside significant enhancements of alkanes, substituted cycloalkanes, TEX, dichloromethane, and chloroform compared to the ground samples, suggesting local seaborne emissions. These findings highlighted the necessity of comprehensive monitoring to better capture long-term VOC emission patterns in the region.