Solubility Of Iron In Atmospheric Aerosols And Related Factors In Marginal Seas, China

The concentration of trace element iron can be the limiting factor of marine primary production. Atmospheric aerosol dry or wet deposition is globally a rather major fraction of the total Fe inputs to the oceans. Solubility of the iron in the aerosol is one of the key factors to the ocean primary production. Many studies have been conducted to study the solubility of iron in atmospheric aerosol. Compared with sub-Saharan Africa dust, solubility studies of trace elements in Asia dust is very limited.In this study,69 total suspended particulate (TSP) samples were collected in china’s Marginal Seas (Bohai Sea 6, Yellow Sea 16, East China Sea 33, South China Sea 14). The total and soluble concentrations of iron were analyzed to investigate the distribution characteristics of iron solubility in different Marginal Seas. This study was concentrated on the related factors of the aerosol iron solubility (e.g. Acid processing, Gravitational setting, Cloud processing, Sea salt loading, transport history, biomass burning.) and eventually evaluate the influence of Asian dust deposition on marine primary production.The results showed that the total concentration of aerosol iron ranked as Bohai Sea (2024ng/m3)>Yellow Sea (1064 ng/m3)>East China Sea (607 ng/m3)>South China Sea (435 ng/m3) in a decreasing order. Iron solubility ranged from 1.5% to 21.3% with the average value of 8.7% in Marginal Seas, China. The solubility of aerosol iron (Fe%) is roughly the same (Bohai Sea:7.4%; Yellow Sea:10.4%; East China Sca:9.7%; South China sea:7.2%).In South China Sea, this study found that the nature source contributed most to the total concentration of iron (FeT). Soluble iron (Fes) exhibited a significantly positive correlation with acid species (nss-SO42-; NO3- and Oxalate), suggesting that iron solubility may be increased by acid processing. Positive correlation between soluble iron and nss-K+ indicated that biomass burning may influence the iron solubility. Biomass burning aerosol makes no contribution to the soluble iron. And biomass burning aerosol was an important source of cloud condensation nuclei associated with clouding processing to enhancing solubility of iron. The correlation between soluble iron and soluble trace elements (As, Pb and Cd) which derived from anthropogenic sources was better than the correlation between the total iron concentration and the corresponding trace elements (As, Pb and Cd). This result indicated that trace elements might undergo similar atmospheric process, which could be explained by the cloud processing.In East China Sea, the concentration of the total iron, soluble iron and anthropogenic pollution were much higher in high-dust samples compared with low-dust samples. In high-dust samples, the solubility of iron in slow and polluted type samples (SP-type) was much higher than fast and clean type samples (FC-type), but close to the low-dust samples. The concentration of total iron ranked as autumn> spring> summer in a decreasing order, and the solubility ranked as summer> spring> autumn. The concentration of soluble iron was positive correlated with acid components suggested that acid processing might increase the solubility of aerosol iron. And the huge difference of iron solubility between FC-type and SP-type samples came to the same conclusion. On the other hand, sea salt may inhibit the dissolution of iron from dust particles.The total suspended particle samples collected in Yellow Sea were classified into two groups:samples were from a northern continental source zone (NCS); samples were mainly from the marine and coastal environments (no-NCS). The solubility of aerosol iron in no-NCS samples (13.5%) was about two times of the NCS samples (7.3%). Cloud processing could increase solubility of iron in NCS samples; the acid processing probably enhanced Fe solubility in no-NCS samples. Significant positive correlation was found between the solubility and surface area to volume (S/V), which suggested that greater solubility at lower dust mass concentration could be due to a larger surface area to volume ratio of the finer dust particles.