Characterization of marine aerosols and precipitation through shipboard observations on the transect between 31° N–32° S in the West Pacific

To characterize the chemical composition, size distributions, and fractional Fe solubility of atmospheric particles over Asian marginal seas, South Indian Ocean and Australian coast, selected water–soluble inorganic and organic species in aerosols and precipitation, trace metals and soluble Fe in aerosols were analyzed by multi–instruments. Results showed that sea salt and non–sea–salt sulfate (nss–SO42–) were the main components in aerosols. Over Asian marginal seas, Cl– and Na+ were the dominant ions in precipitation, accounting for ˜;72% of the total ions. Both SO42– and NO3– accounted for −26% of the total anions, controlling the acidity of the precipitation. Non–sea–salt Ca2+ (nss–Ca2+) accounted for 6.9% of the total cations, dominating the neutralizing component in rainwater. Observed methane sulfonate (MSA) concentrations and MSA/nss–SO42– increased southward. The concentrations of sea salt were affected by wind speeds, which was mainly accumulated in particle size >10 μm. Particle size distributions of nss–SO42– and NH4+ mainly peaked in the fine mode, while NO3– was mainly accumulated in the coarse mode. Oxalate presented a bimodal size distribution pattern in both fine and coarse modes. Based on the air mass back trajectories, enrichment factors and Fe/Al, V/Al ratios, aerosol samples collected over Asian marginal seas could be affected by both long–range transported dust and anthropogenic emissions. Good relationship was found between total dissolved iron and nss–SO42–, indicating that acid processing during long–range transport could play an important role in fractional iron solubility in aerosols. The inverse relationship between atmospheric total Fe and fractional Fe solubility fitted in the global–scale trend. This study implicates that dust and acidic air pollutants from continental sources can interact and affect iron solubility in aerosols in the marine atmosphere. However, due to the small size of samples in this study, more investigations need to be conducted in future.