Ship Emissions as the Largest Contributor to Coastal Atmospheric Black Carbon at a Receptor Island in Southern China

Abstract

Atmospheric black carbon (BC) over coastal regions poses a threat in terms of both climate change and human health. However, the provenance of aerosol BC, particularly its subfractions (char-BC and soot-BC, which have different physicochemical properties), is poorly constrained. Here, we apportioned the sources of char-BC and soot-BC in year-round PM_2.5 samples from a coastal receptor island off southern China. Char-BC dominated, accounting for 88.6 ± 13.2% of the total BC. The two BC subfractions exhibited distinct seasonal variation patterns, which may be attributed to differences in their sources and hydrophilicity. Combustion of liquid fossil fuels, including bunker fuel, diesel, and gasoline, contributed more highly to soot-BC (71.4%) than to char-BC (53.9%). Conversely, combustion of solid fuels, including biomass and coal, contributed more highly to char-BC (44.6%) than to soot-BC (6.7%). Bunker fuel combustion, the dominant portion of ship emissions, was the largest contributor to total BC (46.0%), char-BC (45.2%), and soot-BC (56.4%). This indicates that marine ship emissions, rather than land-based sources including biomass and coal combustion, were the dominant source of atmospheric BC in coastal areas, highlighting the importance of controlling maritime ship emissions.