Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility
<p>Atmospheric deposition is one of the main sources of dissolved iron (Fe) in the ocean surfaces. Atmospheric processes are recognized as controlling fractional Fe solubility (Fe<span class="inline-formula"><sub>sol</sub></span>%) in marine aerosol particles....
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2022-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/9461/2022/acp-22-9461-2022.pdf |
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| author | K. Sakata M. Kurisu M. Kurisu Y. Takeichi A. Sakaguchi H. Tanimoto H. Tanimoto Y. Tamenori A. Matsuki Y. Takahashi Y. Takahashi |
| author_facet | K. Sakata M. Kurisu M. Kurisu Y. Takeichi A. Sakaguchi H. Tanimoto H. Tanimoto Y. Tamenori A. Matsuki Y. Takahashi Y. Takahashi |
| author_sort | K. Sakata |
| collection | DOAJ |
| description | <p>Atmospheric deposition is one of the main sources of dissolved iron (Fe) in
the ocean surfaces. Atmospheric processes are recognized as controlling
fractional Fe solubility (Fe<span class="inline-formula"><sub>sol</sub></span>%) in marine aerosol particles.
However, the impact of these processes on Fe<span class="inline-formula"><sub>sol</sub></span>% remains unclear.
One of the reasons for this is the lack of field observations focusing on
the relationship between Fe<span class="inline-formula"><sub>sol</sub></span>% and Fe species in marine aerosol
particles. In particular, the effects of organic ligands on Fe<span class="inline-formula"><sub>sol</sub></span>%
have not been thoroughly investigated in observational studies. In this
study, Fe species in size-fractionated aerosol particles in the Pacific
Ocean were determined using X-ray absorption fine structure (XAFS)
spectroscopy. The internal mixing states of Fe and organic carbon were
investigated using scanning transmission X-ray microscopy (STXM). The
effects of atmospheric processes on Fe<span class="inline-formula"><sub>sol</sub></span>% in marine aerosol
particles were investigated based on the speciation results. Iron in
size-fractionated aerosol particles was mainly derived from mineral dust,
regardless of aerosol diameter, because the enrichment factor of Fe was
almost 1 in both coarse (PM<span class="inline-formula"><sub>>1.3</sub></span>) and fine aerosol particles
(PM<span class="inline-formula"><sub>1.3</sub></span>). Approximately 80 % of the total Fe (insoluble <span class="inline-formula">+</span> labile
Fe) was present in PM<span class="inline-formula"><sub>>1.3</sub></span>, whereas labile Fe was mainly present in
PM<span class="inline-formula"><sub>1.3</sub></span>. The Fe<span class="inline-formula"><sub>sol</sub></span>% in PM<span class="inline-formula"><sub>>1.3</sub></span> was not significantly
increased (<span class="inline-formula">2.56±2.53</span> %, 0.00 %–8.50 %, <span class="inline-formula"><i>n</i>=20</span>) by the
atmospheric processes because mineral dust was not acidified beyond the
buffer capacity of calcite. In contrast, mineral dust in PM<span class="inline-formula"><sub>1.3</sub></span> was
acidified beyond the buffer capacity of calcite. As a result, Fe<span class="inline-formula"><sub>sol</sub></span>%
in PM<span class="inline-formula"><sub>1.3</sub></span> (0.202 %–64.7 %, <span class="inline-formula"><i>n</i>=10</span>) was an order of magnitude higher
than that in PM<span class="inline-formula"><sub>>1.3</sub></span>. The PM<span class="inline-formula"><sub>1.3</sub></span> contained ferric organic complexes
with humic-like substances (Fe(III)-HULIS, but not Fe-oxalate complexes),
and the abundance correlated with Fe<span class="inline-formula"><sub>sol</sub></span>%. Iron(III)-HULIS was formed
during transport in the Pacific Ocean because Fe(III)-HULIS was not found in
aerosol particles in Beijing and Japan. The pH estimations of mineral dust
in PM<span class="inline-formula"><sub>1.3</sub></span> established that Fe was solubilized by proton-promoted
dissolution under highly acidic conditions (pH <span class="inline-formula"><</span> 3.0), whereas
Fe(III)-HULIS was stabilized under moderately acidic conditions (pH 3.0–6.0). Since the observed labile Fe concentration could not be
reproduced by proton-promoted dissolution under moderately acidic
conditions, the pH of mineral dust increased after proton-promoted
dissolution. The cloud process in the marine atmosphere increases the
mineral dust pH because the dust particles are covered with organic carbon
and Na. The precipitation of ferrihydrite was suppressed by Fe(III)-HULIS
owing to its high water solubility. Thus, the organic complexation of Fe
with HULIS plays a significant role in the stabilization of Fe that was
initially solubilized by proton-promoted dissolution.</p> |
| first_indexed | 2024-04-13T03:49:55Z |
| format | Article |
| id | doaj.art-60c21047b1d346f197d745a315a34076 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-13T03:49:55Z |
| publishDate | 2022-07-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-60c21047b1d346f197d745a315a340762022-12-22T03:03:51ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242022-07-01229461948210.5194/acp-22-9461-2022Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubilityK. Sakata0M. Kurisu1M. Kurisu2Y. Takeichi3A. Sakaguchi4H. Tanimoto5H. Tanimoto6Y. Tamenori7A. Matsuki8Y. Takahashi9Y. Takahashi10Center for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, JapanResearch Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japannow at: Research Institute for Marine Resources Utilization, Japan Agency for Marine-Earth Science and Technology, 2-15, Natsushima-cho, Yokosuka, Kanagawa 237-0061, JapanInstitute of Materials Structure Science, High-Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, JapanFaculty of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, JapanCenter for Global Environmental Research, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, JapanGraduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, JapanJapan Synchrotron Radiation Research Institute/SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5198, JapanInstitute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, JapanInstitute of Materials Structure Science, High-Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, JapanGraduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan<p>Atmospheric deposition is one of the main sources of dissolved iron (Fe) in the ocean surfaces. Atmospheric processes are recognized as controlling fractional Fe solubility (Fe<span class="inline-formula"><sub>sol</sub></span>%) in marine aerosol particles. However, the impact of these processes on Fe<span class="inline-formula"><sub>sol</sub></span>% remains unclear. One of the reasons for this is the lack of field observations focusing on the relationship between Fe<span class="inline-formula"><sub>sol</sub></span>% and Fe species in marine aerosol particles. In particular, the effects of organic ligands on Fe<span class="inline-formula"><sub>sol</sub></span>% have not been thoroughly investigated in observational studies. In this study, Fe species in size-fractionated aerosol particles in the Pacific Ocean were determined using X-ray absorption fine structure (XAFS) spectroscopy. The internal mixing states of Fe and organic carbon were investigated using scanning transmission X-ray microscopy (STXM). The effects of atmospheric processes on Fe<span class="inline-formula"><sub>sol</sub></span>% in marine aerosol particles were investigated based on the speciation results. Iron in size-fractionated aerosol particles was mainly derived from mineral dust, regardless of aerosol diameter, because the enrichment factor of Fe was almost 1 in both coarse (PM<span class="inline-formula"><sub>>1.3</sub></span>) and fine aerosol particles (PM<span class="inline-formula"><sub>1.3</sub></span>). Approximately 80 % of the total Fe (insoluble <span class="inline-formula">+</span> labile Fe) was present in PM<span class="inline-formula"><sub>>1.3</sub></span>, whereas labile Fe was mainly present in PM<span class="inline-formula"><sub>1.3</sub></span>. The Fe<span class="inline-formula"><sub>sol</sub></span>% in PM<span class="inline-formula"><sub>>1.3</sub></span> was not significantly increased (<span class="inline-formula">2.56±2.53</span> %, 0.00 %–8.50 %, <span class="inline-formula"><i>n</i>=20</span>) by the atmospheric processes because mineral dust was not acidified beyond the buffer capacity of calcite. In contrast, mineral dust in PM<span class="inline-formula"><sub>1.3</sub></span> was acidified beyond the buffer capacity of calcite. As a result, Fe<span class="inline-formula"><sub>sol</sub></span>% in PM<span class="inline-formula"><sub>1.3</sub></span> (0.202 %–64.7 %, <span class="inline-formula"><i>n</i>=10</span>) was an order of magnitude higher than that in PM<span class="inline-formula"><sub>>1.3</sub></span>. The PM<span class="inline-formula"><sub>1.3</sub></span> contained ferric organic complexes with humic-like substances (Fe(III)-HULIS, but not Fe-oxalate complexes), and the abundance correlated with Fe<span class="inline-formula"><sub>sol</sub></span>%. Iron(III)-HULIS was formed during transport in the Pacific Ocean because Fe(III)-HULIS was not found in aerosol particles in Beijing and Japan. The pH estimations of mineral dust in PM<span class="inline-formula"><sub>1.3</sub></span> established that Fe was solubilized by proton-promoted dissolution under highly acidic conditions (pH <span class="inline-formula"><</span> 3.0), whereas Fe(III)-HULIS was stabilized under moderately acidic conditions (pH 3.0–6.0). Since the observed labile Fe concentration could not be reproduced by proton-promoted dissolution under moderately acidic conditions, the pH of mineral dust increased after proton-promoted dissolution. The cloud process in the marine atmosphere increases the mineral dust pH because the dust particles are covered with organic carbon and Na. The precipitation of ferrihydrite was suppressed by Fe(III)-HULIS owing to its high water solubility. Thus, the organic complexation of Fe with HULIS plays a significant role in the stabilization of Fe that was initially solubilized by proton-promoted dissolution.</p>https://acp.copernicus.org/articles/22/9461/2022/acp-22-9461-2022.pdf |
| spellingShingle | K. Sakata M. Kurisu M. Kurisu Y. Takeichi A. Sakaguchi H. Tanimoto H. Tanimoto Y. Tamenori A. Matsuki Y. Takahashi Y. Takahashi Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility Atmospheric Chemistry and Physics |
| title | Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility |
| title_full | Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility |
| title_fullStr | Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility |
| title_full_unstemmed | Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility |
| title_short | Iron (Fe) speciation in size-fractionated aerosol particles in the Pacific Ocean: The role of organic complexation of Fe with humic-like substances in controlling Fe solubility |
| title_sort | iron fe speciation in size fractionated aerosol particles in the pacific ocean the role of organic complexation of fe with humic like substances in controlling fe solubility |
| url | https://acp.copernicus.org/articles/22/9461/2022/acp-22-9461-2022.pdf |
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