Chemical characterizations and sources of PM2.5 over the offshore Eastern China sea: Water soluble ions, stable isotopic compositions, and metal elements

Abstract

Marine aerosols are mainly sea salt or secondary-formation non-sea salt (nss) inorganic ions and organic compounds released from the ocean, which are modified by substances from terrestrial sources via long-distance transport. Atmospheric particulate matter (PM2.5) was collected during a ship campaign over the offshore eastern China Sea (OECS) from April 20, 2018 to May 18, 2018. Nine water-soluble ions (WSIs), organic carbon (OC), elemental carbon (EC), stable carbon/nitrogen isotopes, and twenty-six metal elements were analyzed. The average concentrations of WSIs, OC, and EC were 13.73 ± 4.89, 2.55 ± 1.95, and 0.72 ± 0.56 μg/m3, respectively. SO42−, NH4+, and NO3− were the predominant species among the WSIs, accounting for 53.2, 16.1, and 11.6% of the total ion mass, respectively. A strong correlation between OC and EC (r2 = 0.79) was found, indicating that they may be derived from common sources. The δ13CTC values ranged from −26.44 to −23.63‰, with an average of −25.82 ± 0.67‰, while δ15NTN values were in the range of −2.19 and 6.97‰, with an average of 5.40 ± 2.05‰. The overlapping isotopic ratios combined with the correlation results suggested that emissions from coal-fired activities and biomass burning were major factors affecting marine aerosols in the OECS. Twenty-six metal elements were classified into natural, anthropogenic, or mixed sources based on their enrichment factors, and more than 60% of the elements were affected by anthropogenic sources. Positive matrix factorization (PMF) analysis identified five potential source factors of PM2.5, including marine sources, vehicular exhaust, crustal sources, secondary formation, and combustion sources, while anthropogenic sources (vehicular exhaust, secondary formation, and combustion sources) accounted for 78.0% of all sources.