EGU2020-423
https://doi.org/10.5194/egusphere-egu2020-423
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Role of Oxalic acid on Fractional Solubility of Aerosol Iron over Coastal Ocean: Evidence from compound-specific stable carbon isotopic composition and diagnostic mass ratios

Srinivas Bikkina1,2,3, Kimitaka Kawamura1,3, Manmohan Sarin2, and Eri Tachibana3
Srinivas Bikkina et al.
  • 1Chubu Institute for Advanced Studies, Chubu University, Kasugai, 487-8501, Aichi, Japan
  • 2Physical Research Laboratory, Ahmedabad, 380 009, India
  • 3Institute of Low Temperature Science, Hokkaido University, Sapporo, 060-0819, Japan

Atmospheric transport and the subsequent air-to-sea deposition of water-soluble iron (Fews), an essential micronutrient for the phytoplankton growth, have a profound influence on the biogeochemical cycles of carbon and nitrogen. Sources of Fews include contributions from poorly soluble natural mineral dust and highly soluble anthropogenic aerosols from biomass burning emissions and fossil-fuel combustion in the continental outflows. Apart from the source/emission contributions, atmospheric processing of aerosol iron (FeTot) by inorganic acidic species (e.g., non-sea-salt or nss-SO42- and NO3-) and/or organic acids also affect the supply of Fews to the surface waters that are downwind of pollution sources. Among these, the least understood process is the oxalic acid-mediated photochemical cycling of Fews. Laboratory studies have clearly demonstrated an enhancement in the fractional solubility of aerosol iron (i.e., Fews (%) = Fews/FeTot ×100) via the oxalic acid complexation with FeTot and subsequent photochemical reduction process. However, lacking support from the field measurements limits our ability to incorporate the proposed mechanism in the current biogeochemistry models. This study is designed with the overarching goal of investigating the role of oxalic acid on the Fews (%) over a coastal ocean (i.e., the Bay of Bengal: BoB) influenced by the atmospheric outflow from the Indo-Gangetic Plain (IGP) and South-east Asia (SEA) during the winter season. We analysed 31 PM2.5 samples for the mass concentrations of FeTot, Fews and other chemical composition including nss-SO42-, NO3-, oxalic acid and related polar compounds as well as stable carbon isotopic composition of oxalic acid (δ13Coxalic). Strong positive linear relationship of oxalic acid with FeTot and significant inverse linear relationship between δ13Coxalic and Fews over the BoB clearly emphasize the role of oxalic acid on the Fews (%).  These findings comply with the notion that oxalic acid formed from the precursor water-soluble organic acids in the deliquescent aerosols, is complexed with aerosol-Fe and undergoes through successive photochemical reactions, contributing to an overall increase in the Fews (%). 

How to cite: Bikkina, S., Kawamura, K., Sarin, M., and Tachibana, E.: Role of Oxalic acid on Fractional Solubility of Aerosol Iron over Coastal Ocean: Evidence from compound-specific stable carbon isotopic composition and diagnostic mass ratios , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-423, https://doi.org/10.5194/egusphere-egu2020-423, 2019

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