Morphological features and water solubility of iron in aged fine aerosol particles over the Indian Ocean
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Published:2023-09-11
Issue:17
Volume:23
Page:10117-10135
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Ueda SayakoORCID, Iwamoto Yoko, Taketani Fumikazu, Liu MingxuORCID, Matsui HitoshiORCID
Abstract
Abstract. Atmospheric transport of iron (Fe) in fine anthropogenic aerosol
particles is an important route of soluble Fe supply from continental areas
to remote oceans. To elucidate Fe properties of aerosol particles over
remote oceans, we collected atmospheric aerosol particles over the Indian
Ocean during the RV Hakuho Maru KH-18-6 cruise. After aerosol particles were collected
using a cascade impactor, particles of 0.3–0.9 µm aerodynamic diameter
on the sample stage were analyzed using transmission electron microscopy
(TEM) with an energy-dispersive X-ray spectrometry analyzer. The particle
shape and composition indicated that most particles collected north of the
Equator were composed mainly of ammonium sulfate. Regarding the particle
number fraction, 0.6 %–3.0 % of particles contained Fe, which mostly
co-existed with sulfate. Of those particles, 26 % of Fe occurred as metal
spheres, often co-existing with Al or Si, regarded as fly ash; 14 % as
mineral dust; and 7 % as iron oxide aggregates. Water dialysis analyses of
TEM samples indicated Fe in spherical fly ash as being almost entirely insoluble
and Fe in other morphological-type particles as being partly soluble (65 % Fe
mass on average). Global model simulations mostly reproduced observed Fe
mass concentrations in particulate matter with a diameter of less than 2.5 µm (PM2.5) collected using a high-volume air sampler,
including their north–south contrast during the cruise. In contrast, a
marked difference was found between the simulated mass fractions of Fe
mineral sources and the observed Fe types. For instance, the model
underestimated anthropogenic aluminosilicate (illite and kaolinite) Fe
contained in matter such as fly ash from coal combustion. Our observations
revealed multiple shapes and compositions of Fe minerals in particles over
remote ocean areas and further suggested that their solubilities after
aging processes differ depending on their morphological and mineral types.
Proper consideration of such Fe types at their sources is necessary for
accurately estimating atmospheric Fe effects on marine biological activity.
Funder
Ministry of Education, Culture, Sports, Science and Technology Environmental Restoration and Conservation Agency
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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