Anthropogenic sources and air mass transport affect spatial and seasonal variations of ambient halocarbons in southeastern China

Halocarbons play a vital role in ozone depletion and global warming, and are regulated by the Montreal Protocol (MP) and its amendments. China has been identified as an important contributor to the halocarbon emissions, but the regional sources of halocarbons in China are not yet well comprehended. To investigate the characteristics, emissions, and source profiles, this study conducted a field campaign in Xiamen, a coastal city in southeastern China. Higher enhancements were found in the unregulated halocarbons (CH₃Cl, CH₂Cl₂, CHCl₃) than in the MP eliminated species (CCl₄, CH₃Br) and the MP controlled species (HCFCs, HFCs). Many of the measured halocarbons varied seasonally and regionally, depending on the anthropogenic sources and atmospheric transport. Backward trajectory analysis showed that the air masses from inland were polluted over Shandong, Hebei, and northern Fujian in the cold season, while the air masses from the sea in the warm season were clean. Different air masses in two seasons were associated with the halocarbon patterns in the study area. Industrial activities, especially solvent usage, were the primary sources of halocarbons. The emission hot spots in Fujian Province were concentrated in Sanming, Fuzhou, and Xiamen, and the unregulated halocarbons made the largest contribution. This study provides an insight for a deep understanding of the characteristics and potential sources of halocarbons, and for strengthened management of halocarbons in China.