Temporal variations and chemical characteristics of marine PM 2.5 at Dongsha Islands, South China Sea: Three-year measurement

The study of long-range transport effects on marine fine particles (PM 2.5 ), particularly in remote sites such as the Dongsha Islands, is pivotal for advancing our understanding of air pollution dynamics on a regional scale and for formulating effective environmental policies. PM 2.5 concentrations were examined over three consecutive years and grouped based on their transport routes. The backward trajectory simulation revealed that high PM 2.5 concentrations were observed in the West Channel, originating from North and Central China, the Korean Peninsula, and the Japanese Islands, opposed to the East Channel . High PM 2.5 concentrations, commonly observed in winter and spring, were mainly attributed to the Asian Northeastern Monsoons. Water-soluble inorganic ions constituted the major components, accounting for 37.8-48.7% of PM 2.5 , and followed by metal elements (15.5-20.0%), carbons (7.5-13.3%), levoglucosan (0.01-0.17%), and organic aerosols (0.2-2.2%). Secondary inorganic aerosols as the dominant source accounted for 8.3-24.7% of PM 2.5 , while sea salts were the secondary major contributor. High levoglucosan contribution (3.8-7.2%) in winter and spring was attributed to biomass burning, mainly from the Indochina Peninsula. Chemical mass balance receptor modeling resolved that major sources of PM 2.5 were secondary sulfate, sea salts, fugitive dust, and industrial boilers. This study concluded that the long-range transport of PM 2.5 gradually increased since fall, contributing 52.1-74.3%, highlighting its substantial impact on PM 2.5 in all seasons except summer.