Preprints
https://doi.org/10.5194/acp-2021-460
https://doi.org/10.5194/acp-2021-460

  24 Jun 2021

24 Jun 2021

Review status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Contribution of combustion Fe in marine aerosols over the northwestern Pacific estimated by Fe stable isotope ratios

Minako Kurisu1, Kohei Sakata2, Mitsuo Uematsu3,4, Akinori Ito5, and Yoshio Takahashi6 Minako Kurisu et al.
  • 1Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15, Natsushima-cho, Yokosuka, Kanagawa, 237-0061, Japan
  • 2Center for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan
  • 3Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba 277-8564, Japan
  • 4Center for Environmental Science in Saitama, Saitama 347-0115, Japan
  • 5Research Institute for Global Change, JAMSTEC, Yokohama, Kanagawa, 236-0001, Japan
  • 6Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Abstract. The source apportionment of aerosol iron (Fe), including natural and combustion Fe, is an important issue because aerosol Fe can enhance oceanic primary production in the surface ocean. Based on our previous finding that combustion Fe emitted by evaporation processes has Fe isotope ratios (δ56Fe) that are approximately 4 ‰ lower than those of natural Fe, this study aimed to distinguish aerosol Fe sources over the northwestern Pacific using two size-fractionated marine aerosols. The δ56Fe values of fine and coarse particles from the eastern or northern Pacific were found to be similar to each other, ranging from 0.0 to 0.4 ‰. Most of them were close to the crustal average, suggesting the dominance of natural Fe. On the other hand, particles from East Asia demonstrated lower δ56Fe values in fine particles (−0.5 to −2.2 ‰) than in coarse particles (on average 0.1 ‰). The correlations between the δ56Fe values and the enrichment factors of lead and vanadium suggested that the low δ56Fe values obtained were due to the presence of combustion Fe. The δ56Fe values of the soluble component of fine particles in this region were lower than the total, indicating the preferential dissolution of combustion Fe. In addition, we found a negative correlation between the δ56Fe value and the fractional Fe solubility in air masses from East Asia. These results suggested that the presence of combustion Fe is an important factor in controlling the fractional Fe solubility in air masses from East Asia, whereas other factors were more important in the other areas. By assuming typical δ56Fe values for combustion and natural Fe, the contribution of combustion Fe to the total (acid-digested) Fe in aerosols was estimated to reach up to 50 % of fine and 21 % of bulk (coarse + fine) particles in air masses from East Asia, whereas its contribution was small in the other areas. The contribution of combustion Fe to the soluble Fe component estimated for one sample was approximately twice as large as the total, indicating the importance of combustion Fe as a soluble Fe source, despite lower emissions than the natural. These isotope-based estimates were compared with those estimated using an atmospheric chemical transport model (IMPACT), in which the fractions of combustion Fe in fine particles, especially in air masses from East Asia, were consistent with each other. In contrast, the model estimated a relatively large contribution from combustion Fe in coarse particles, probably because of the different characteristics of combustion Fe that are included in the model calculation and the isotope-based estimation. This highlights the importance of observational data of δ56Fe for size-fractionated aerosols to scale the combustion Fe emission by the model. The average deposition fluxes of soluble Fe to the surface ocean were 1.4 and 2.9 nmol m−2 day−1 from combustion and natural aerosols, respectively, in air masses from East Asia, which suggests combustion Fe could be an important Fe source to the surface seawater among other Fe sources. Distinguishing Fe sources using the δ56Fe values of marine aerosols and seawater is anticipated to lead to a more quantitative understanding of the Fe cycle in the atmosphere and surface ocean.

Minako Kurisu et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-460', Anonymous Referee #1, 17 Jul 2021
    • AC1: 'Replies on RC1 and RC2 (acp-2021-460)', Minako Kurisu, 16 Sep 2021
  • RC2: 'Comment on acp-2021-460', Anonymous Referee #2, 01 Aug 2021
    • AC1: 'Replies on RC1 and RC2 (acp-2021-460)', Minako Kurisu, 16 Sep 2021
  • AC1: 'Replies on RC1 and RC2 (acp-2021-460)', Minako Kurisu, 16 Sep 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-460', Anonymous Referee #1, 17 Jul 2021
    • AC1: 'Replies on RC1 and RC2 (acp-2021-460)', Minako Kurisu, 16 Sep 2021
  • RC2: 'Comment on acp-2021-460', Anonymous Referee #2, 01 Aug 2021
    • AC1: 'Replies on RC1 and RC2 (acp-2021-460)', Minako Kurisu, 16 Sep 2021
  • AC1: 'Replies on RC1 and RC2 (acp-2021-460)', Minako Kurisu, 16 Sep 2021

Minako Kurisu et al.

Minako Kurisu et al.

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Short summary
Aerosol iron (Fe) input can enhance oceanic primary production. We analyzed Fe isotope ratios of size fractionated aerosols over the northwestern Pacific to evaluate the contribution of natural and combustion Fe. It was found that combustion Fe was an important soluble Fe source in marine aerosols and possibly in surface seawater when air masses were from East Asia. This study showed the applicability of Fe isotope ratios for a more quantitative understanding of Fe cycle in the surface ocean.
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