Source characterization of VOCs at a coastal site in Hong Kong

Volatile organic compounds (VOCs) are important gaseous constituents in the troposphere, impacting local and regional air quality, human health, and climate both directly and indirectly (IPCC, 2013). With the participation of nitrogen oxides (NO_x), oxidation of VOCs leads to tropospheric ozone (O₃) formation, causing regional photochemical smog (Atkinson, 2000). In recent years, with the decline of ambient concentrations of other pollutants (e.g., fine particulate matter), the concentrations of O₃ in many locations increased. Therefore, accurately apportioning the emission sources of ambient VOCs and then controlling them more effectively will play an important role in reducing O₃ and secondary organic aerosol pollution in the atmosphere and improving public health.

  In this study, field measurements were conducted at a coastal site (Hok Tsui; HT) in Hong Kong from October to November 2020 with proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS). VOC data coupled with air mass back trajectory cluster analysis and receptor modelling were applied to discuss the pollution pattern, regional transport, and emission sources of ambient VOCs at Hok Tsui in autumn 2020. Seven sources were identified from positive matrix factorization (PMF) analysis, namely vehicular + industrial, solvent usage, primary oxygenated VOCs (OVOCs), secondary OVOCs 1, secondary OVOCs 2 (aged), biogenic emissions, and background + biomass burning, contributing on average to 20.8%, 10.5%, 13.1%, 33.6%, 6.7%, 4.3%, and 10.9% of total VOC mixing ratios, respectively. Secondary OVOCs and vehicular + industrial emissions are the vital sources of ambient VOCs at Hok Tsui supersite. Integrated with backward trajectory analysis, long-range transport of air masses from inland and coastal regions of Southeast China brought more hydrocarbons from vehicular and industrial sources, and consequently more OVOCs in aged air masses. The results of this study highlighted the regional transport of anthropogenic VOCs should be considered in control strategies of VOCs and secondary air pollutants.