Characteristics and source origin analysis of halogenated hydrocarbons in Hong Kong.

Despite being regulated globally for almost three decades, halocarbon continues to play a vital role in climate change and ozone layer because of its long lifetime in the ambient air. In recent years, unexpected halocarbon emissions have been found in Asia, raising concerns about ozone recovery. As a number of studies focused on halocarbon variations and source profiles, there is an increasing need to identify halocarbon source origins. In this study, an eight-month regular air sampling was conducted at a coastal site in Hong Kong from November 2020 to June 2021, and seventeen halocarbon species were selected for extensive investigation after advanced sample analysis in our laboratory. The temporal variations of halocarbon mixing ratio enhancements were analyzed, and the spatial variations of source origins were investigated by wind sectors and backward trajectory statistics. 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. The source apportionment analysis estimates the contributions from six emission sectors on measured halocarbons, including solvent usage (43.57 ± 4.08 %), refrigerant residues (17.05 ± 5.71 %), cleaning agent/chemical production (13.18 ± 4.76 %), refrigerant replacements (13.06 ± 2.13 %), solvent residues (8.65 ± 3.28 %), and foaming agent (4.49 ± 1.08 %). Trajectories statistical analysis suggests that industrial solvent was mainly contributed by eastern China (i.e., Shandong and YRD), cleaning agent/chemical production was spread over southeast China (i.e., YRD and Fujian), and refrigeration replacements were dominant in Hong Kong surrounding regions. 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.

Molecular and elemental marker-based source apportionment of fine particulate matter at six sites in Hong Kong, China.

Source apportionment of PM2.5 was performed using positive matrix factorization (PMF) based on chemical speciation data from 24-h filters collected throughout 2015 at six sampling sites of varying urban influences in Hong Kong. The input data include major inorganic ions, organic and elemental carbon, elements, and organic tracers. Nine factors were resolved, including (1) secondary sulfate formation process, (2) secondary nitrate formation process, (3) industrial emissions, (4) biomass burning, (5) primary biogenic emissions, (6) vehicle emissions, (7) residual oil combustion, (8) dust, and (9) aged sea salt. The PMF-resolved factor contributions in conjunction with air mass back trajectories showed that the two major sources for PM2.5 mass, secondary sulfate (annual: 41%) and secondary nitrate (annual: 9.9%), were dominantly associated with regional and super-regional pollutant transport. Vehicular emissions are the most important local source, and its contributions exhibit a clear spatial variation pattern, with the highest (6.9 µg/m3, 24% of PM2.5) at a downtown roadside location and the lowest (0.4 µg/m3, 2.0% PM2.5) at two background sites away from city centers. The ability of producing a more reliable source separation and identifying new sources (e.g. primary biogenic source in this study) was a direct advantageous result of including organic tracers in the PMF analysis. PMF analysis conducted on the same dataset in this study but without including the organic tracers failed to separate the biomass burning emissions and industrial/coal combustion emissions. PMF analysis without the organic tracers would also over-apportion the contribution of vehicular emissions to PM2.5, which would bias the evaluation of the effectiveness of vehicle-related control measures. This work demonstrates the importance of organic markers in achieving more comprehensive and less biased source apportionment results.