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Lewis, TR, Gómez Martín, JC, Blitz, MA et al. (3 more authors) (2020) Determination of the absorption cross sections of higher-order iodine oxides at 355 and 532 nm. Atmospheric Chemistry and Physics, 20 (18). pp. 10865-10887. ISSN 1680-7316
Abstract
Iodine oxides (IxOy) play an important role in the atmospheric chemistry of iodine. They are initiators of new particle formation events in the coastal and polar boundary layers and act as iodine reservoirs in tropospheric ozone-depleting chemical cycles. Despite the importance of the aforementioned processes, the photochemistry of these molecules has not been studied in detail previously. Here, we report the first determination of the absorption cross sections of IxOy, x=2, 3, 5, y=1–12 at λ=355 nm by combining pulsed laser photolysis of I2∕O3 gas mixtures in air with time-resolved photo-ionization time-of-flight mass spectrometry, using NO2 actinometry for signal calibration. The oxides selected for absorption cross-section determinations are those presenting the strongest signals in the mass spectra, where signals containing four iodine atoms are absent. The method is validated by measuring the absorption cross section of IO at 355 nm, σ355nm,IO=(1.2±0.1) ×10−18 cm2, which is found to be in good agreement with the most recent literature. The results obtained are σ355nm,I2O3<5×10−19 cm2 molec.−1, σ355nm,I2O4= (3.9±1.2)×10−18 cm2 molec.−1, σ355nm,I3O6= (6.1±1.6)×10−18 cm2 molec.−1, σ355nm,I3O7= (5.3±1.4)×10−18 cm2 molec.−1, and σ355nm,I5O12= (9.8±1.0)×10−18 cm2 molec.−1. Photodepletion at λ=532 nm was only observed for OIO, which enabled determination of upper limits for the absorption cross sections of IxOy at 532 nm using OIO as an actinometer. These measurements are supplemented with ab initio calculations of electronic spectra in order to estimate atmospheric photolysis rates J(IxOy). Our results confirm a high J(IxOy) scenario where IxOy is efficiently removed during daytime, implying enhanced iodine-driven ozone depletion and hindering iodine particle formation. Possible I2O3 and I2O4 photolysis products are discussed, including IO3, which may be a precursor to iodic acid (HIO3) in the presence of HO2.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © Author(s) 2020. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Chemistry (Leeds) > Physical Chemistry (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 24 Sep 2020 15:14 |
Last Modified: | 24 Sep 2020 15:14 |
Status: | Published |
Publisher: | Copernicus Publications |
Identification Number: | 10.5194/acp-20-10865-2020 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:165915 |
Available Versions of this Item
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Determination of the absorption cross-sections of higher order iodine oxides at 355 nm and 532 nm. (deposited 26 Jun 2020 11:05)
- Determination of the absorption cross sections of higher-order iodine oxides at 355 and 532 nm. (deposited 24 Sep 2020 15:14) [Currently Displayed]