Spatio-seasonal characterization and emissions estimation of ozone-depleting substances in the Pearl River Delta, China

Although chlorofluorocarbons (CFCs), CH3Br and chlorinated solvents such as CH3Cl3 and CCl4 have been entirely phased out in the Pearl River Delta (PRD) region, these compounds still exist chronically in atmosphere. In this study, ambient air samples were collected at twenty sites in the PRD region in winter (November to December 2019) and summer (August 2020) to characterize the spatio-seasonal variation of ozone-depleting substances (ODS), including CFC-11, CFC-12, CFC-113, CFC-114, CH3CCl3, CCl4, and CH3Br, and to estimate their emissions. Our observation showed that the average mixing ratios of the target ODS in the PRD region were 16.5%-92.5% lower compared with their reported levels in 2001 except for CFC-114, which basically remained at a constant level. Among the seven ODS, the average mixing ratio of CH3CCl3 declined most rapidly. The mixing ratios of the target ODS were higher in summer than in winter. Higher mixing ratios of the target ODS were observed in the two PRD urban background sites than the northern hemisphere background level, suggesting the existence of local emission sources. The spatial distribution indicated that the Foshan-Guangzhou-Dongguan-Shenzhen corridor area had the highest mixing ratios of the target ODS. Based on the CO-tracer ratio method, the estimated emissions of CFC-11, CFC-12, CFC-113, CFC-114, CH3Br, CH3CCl3 and CCl4 were 1.2, 0.8, 0.3, 0.2, 0.1, 0.1 and 0.4 kt/year, respectively. CFCs showed a very slow reduction in emission since 2008 in general, and the estimated emissions of CH3CCl3 and CCl4 gradually declined from the high value reported in 2004 while CH3Br kept the same level. The findings of this study can help to get a better understanding of the emissions status of ODS in the PRD region and provide valuable information for further reduction processes.