Sources of Chloride in Marine Aerosol over the Yellow Sea and Bohai Sea

Abstract:

Due to significant contribution of anthropogenic sources to fine particles in China, more acidic species and chloride are transported into adjacent seas under westerly, playing an important role in marine atmospheric chemistry. However, studies on particulate chloride pollution and sources in costal China seas are still very limited, especially for cruise measurements. To investigates the source characteristics and spatial distribution of particulate chloride over the Bohai Sea (BS), North Yellow Sea (NYS) and South Yellow Sea (SYS), offline PM_2.5 samples were collected by a high-volume sampler and a low-volume sampler in November 2012. Multiple chemical species were analyzed including organic carbon, elemental carbon, metals, and water-soluble inorganic ions including chloride.

Our results show that (1) the average Cl^- concentration in BS (0.79 mg/m³) was higher than that in NYS (0.26 mg/m³) and SYS (0.20 mg/m³). Such spatial pattern was also found for Pb, Zn, Fe, K, Mn, (2) with the increase of latitude, the ratio of Cl^- to Na⁺ exhibited an increasing trend. The ratio of most samples in Bohai Sea exceeded 1.80 (Cl^-/Na⁺ ratio in seawater), indicating a strong anthropogenic source input of Cl^- in Bohai Sea, (3) contrary to the Cl^- enrichment in BS, clear Cl^- depletion was found in South Yellow Sea with the average percentage of Cl^- depletion up to 71%, (4) from north to south, the acidic species that contributed to Cl^- depletion varied, (5) from the comparison of the ratio of Cl^- to Na⁺ and Cl^- to Pb between source profiles and ambient cruise measurement, the chloride enrichment in Bohai Sea was primarily due to residential coal combustion, (6) combined with the result of the backward trajectory, the air mass changes from a land source to an ocean source from north to south, confirming that marine aerosol in the Bohai Sea was more affected by anthropogenic pollutants.