First X-ray Spectroscopic Observations of Atmospheric Titanium Species: Size Dependence and the Emission Source

Takahashi, Yoshio; Takano, Shotaro; Matsuki, Atsushi; Sakaguchi, Aya; Tanimoto, Hiroshi

doi:10.1021/acs.est.1c02000

Cited by 8 publications

(3 citation statements)

References 70 publications

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“…5d). This result is consistent with previous studies because Asian dust, especially aluminosilicate, in PM 1.3 is internally mixed with sulfate (Sullivan et al, 2007;Fitzgerald et al, 2015;Li et al, 2017;Sakata et al, 2021). Therefore, the acidification of mineral dust by coal-derived SO 2 or H 2 SO 4 during transport in East Asia is the dominant reason for the high Fe sol % in PM 1.3 collected in the WPO.…”

Section: Size Distributions Of Fe and Al Concentrationssupporting

confidence: 92%

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

et al. 2022

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Abstract. 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 (Fesol%) in marine aerosol particles. However, the impact of these processes on Fesol% remains unclear. One of the reasons for this is the lack of field observations focusing on the relationship between Fesol% and Fe species in marine aerosol particles. In particular, the effects of organic ligands on Fesol% 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 Fesol% 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>1.3) and fine aerosol particles (PM1.3). Approximately 80 % of the total Fe (insoluble + labile Fe) was present in PM>1.3, whereas labile Fe was mainly present in PM1.3. The Fesol% in PM>1.3 was not significantly increased (2.56±2.53 %, 0.00 %–8.50 %, n=20) by the atmospheric processes because mineral dust was not acidified beyond the buffer capacity of calcite. In contrast, mineral dust in PM1.3 was acidified beyond the buffer capacity of calcite. As a result, Fesol% in PM1.3 (0.202 %–64.7 %, n=10) was an order of magnitude higher than that in PM>1.3. The PM1.3 contained ferric organic complexes with humic-like substances (Fe(III)-HULIS, but not Fe-oxalate complexes), and the abundance correlated with Fesol%. 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 PM1.3 established that Fe was solubilized by proton-promoted dissolution under highly acidic conditions (pH < 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.

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Section: Size Distributions Of Fe and Al Concentrationssupporting

confidence: 92%

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

et al. 2022

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“…Transition metal oxides in dust act as a photocatalyst that yields electronhole pairs, followed by the formation of reactive oxygen species (ROS) such as hydroxyl radicals ( q OH), superoxides (O q − 2 ), hydroperoxyl radicals (HO q 2 ), and dissociated active oxygen species (O * ) (Chen et al, 2012;Abou-Ghanem et al, 2020;T. Wang et al, 2020b;Sakata et al, 2021). Apart from the site-blocking effect under dark conditions, irradiated Al-bearing constituents additionally facilitate the sulfate formation.…”

Section: Driving Factors Of the Dust Surfacementioning

confidence: 99%

Significant formation of sulfate aerosols contributed by the heterogeneous drivers of dust surface

et al. 2022

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Abstract. The importance of dust heterogeneous oxidation in the removal of atmospheric SO2 and formation of sulfate aerosols is not adequately understood. In this study, the Fe-, Ti-, and Al-bearing components, Na+, Cl−, K+, and Ca2+ of the dust surface, were discovered to be closely associated with the heterogeneous formation of sulfate. Regression models were then developed to make a reliable prediction of the heterogeneous reactivity based on the particle chemical compositions. Further, the recognized gas-phase, aqueous-phase, and heterogeneous oxidation routes were quantitatively assessed and kinetically compared by combining the laboratory work with a modelling study. In the presence of 55 µg m−3 airborne dust, heterogeneous oxidation accounts for approximately 28.6 % of the secondary sulfate aerosols during nighttime, while the proportion decreases to 13.1 % in the presence of solar irradiation. On the dust surface, heterogeneous drivers (e.g. transition metal constituents, water-soluble ions) are more efficient than surface-adsorbed oxidants (e.g. H2O2, NO2, O3) in the conversion of SO2, particularly during nighttime. Dust heterogeneous oxidation offers an opportunity to explain the missing sulfate source during severe haze pollution events, and its contribution proportion in the complex atmospheric environments could be even higher than the current calculation results. Overall, the dust surface drivers are responsible for the significant formation of sulfate aerosols and have profound impacts on the atmospheric sulfur cycling.

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“…Recent studies proposed that transition metal oxides in dust act as photocatalyst that yields electron-hole pairs (Chen et al, 2012;Abou-Ghanem et al, 2020;Sakata et al, 2021), as reflected by the positive correlation between the content of Ti and the sulfate production enhanced by the simulated solar irradiation. The abundance of Al associates positively with the photoinduced sulfate enhancement as well.…”

Section: Driving Factors Of Dust Surfacementioning

confidence: 99%

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2022

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First X-ray Spectroscopic Observations of Atmospheric Titanium Species: Size Dependence and the Emission Source

Cited by 8 publications

References 70 publications

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

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

Significant formation of sulfate aerosols contributed by the heterogeneous drivers of dust surface

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