Characteristics and source apportionment of volatile organic compounds (VOCs) at a coastal site in Hong Kong

Highlights: • VOCs concentrations were measured online by PTR-MS during autumn in Hong Kong. • OVOCs were the dominant species with potential for ozone formation. • The largest contributor to ambient VOCs was biomass burning during campaign. • The air pollution in Hong Kong was strongly influenced by urban plumes from GBA/PRD and by oceanic emissions. Volatile organic compounds (VOCs) that are emitted from biomass burning, vehicle exhaust, and industrial emissions play a vital role in the formation of ozone (O₃) and secondary organic aerosols (SOA). Since VOCs are the precursors of O₃ and aerosol pollution which have become the world's most emergent environmental problems, a field measurement study focused on VOCs was carried out from 27 August to 10 October 2018 in a rural coastal site in Hong Kong. During the campaign, 13 VOC species were detected continuously with proton-transfer-reaction quadrupole mass spectrometry, and their effects on photochemical air pollution were studied. Methanol was the most abundant species among the measured VOCs (average concentration, 3.73 ± 3.26 ppb), and higher concentrations of oxygenated VOCs were found than reported in previous studies of atmospheric chemistry in rural areas. Diurnal variations were observed in the concentrations of various VOC species, indicating that the VOC concentrations were influenced by photochemical reactions. The amount of O₃ formation was estimated based on the maximum incremental reactivity scale of the VOCs. The top five contributors to O₃ formation in Hong Kong (in order) were isoprene (13.46 μg/m³), methyl ethyl ketone (12.74 μg/m³), xylene (8.52 μg/m³), acetaldehyde (8.22 μg/m³), and acrolein (4.32 μg/m³). Receptor model positive matrix factorization (PMF) was used to identify the dominant emission sources and evaluate their corresponding contributions to VOCs. Five major VOC sources were identified with the PMF method, including (1) industry and vehicle-related sources (8.1%), (2) biogenic emissions (5.5%), (3) biomass burning (63.7%), (4) secondary formation (9.2%), and (5) ship-related emissions (13.5%). The source apportionment results from PMF analysis show that the sampling site at the southeastern tip of Hong Kong was strongly influenced by urban plumes from the Guangdong–Hong Kong–Macao Greater Bay Area/Pearl River Delta region and by oceanic emissions.