Novel Triple-Oxygen Isotope Study Indicates Unprecedented Ozone-Particulate Interaction Pathways in Atmospheric Pollution Chemistry - PubMed (original) (raw)
Novel Triple-Oxygen Isotope Study Indicates Unprecedented Ozone-Particulate Interaction Pathways in Atmospheric Pollution Chemistry
Mao-Chang Liang et al. ACS Omega. 2025.
Abstract
Ozone plays a fundamental role in the chemistry of the atmosphere, mediating oxidation reactions in phases and at phase boundaries. Here, we investigate the least-explored solid-phase heterogeneous processes involving ozone to understand the reaction pathways of O3 with airborne aerosols. Using triple oxygen isotope ratios as tracers, we found that the ozone reaction oxidizes organic particles and produces carbon dioxide, with oxygen atoms largely from O3. Along with the formation of CO2, an equal amount of O2 from water decomposition is inferred. Chemical reaction kinetics, however, is yet to be identified. One hypothetical pathway is through Criegee intermediates, formed by the reaction of ozone with aldehyde/ketone-like organic compounds (unsaturated hydrocarbons) catalyzed by metal oxides. Inclusion of the process in a chemistry-transport model could yield a significant change in the ozone budget. The study shows the importance of ozone-induced heterogeneous chemical reactions on aerosol surfaces occurring in polluted atmospheres.
© 2025 The Authors. Published by American Chemical Society.
Conflict of interest statement
The authors declare no competing financial interest.
Figures
Figure 1
(A) The Δ17O values of CO2 are a function of CO2 produced against the ratio of the excess and total amount of CO2 (ΔAmnt/Amnt(CO2)). The two are well correlated with _R_2 = 0.98. The more the CO2 produced, the higher the Δ17O values. The experimental points fall along a line, showing that the Δ17O value of the final CO2 is determined by two end members: excess CO2 with nonzero Δ17O produced from O3 oxidation and the pre-existing CO2 with essentially zero Δ17O. (B) Following the binary mixing calculation of the aforementioned two endmembers, the experimental data are well reproduced, following closely the slope of unity (solid line). The least-squared linear regression yields a slope of 0.99 ± 0.03 and an intercept of 0.66 ± 0.13 with _R_2 = 0.99. The slope of 3/4 denoted by the dashed line is expected if the terminal ozone atoms are only involved.
Figure 2
(A) The deviation of the Δ17O value of the final O2 + O3 from the initial O3 (ΔΔ17Ο(Ο2 + Ο3)), as a function of the amount of CO2 produced (ΔAmnt(CO2)). The _R_2 value (with intercept zero) is 0.94. This suggests that in the final O2 + O3, there are two components: ozone-derived (counting O2 + O3) one having high Δ17O from the initial O3 and another one with an amount likely affected by the new CO2 with a different Δ17O value. (B) Assuming simple two-component mixing (from O3 with nonzero Δ17O and from water with zero Δ17O; see text for details), the experimental values of the final O2 + O3 are well reproduced, following closely the solid line (1:1). The least-squared linear regression (with zero intercept) yields a slope of 0.98 ± 0.02 with _R_2 = 0.99.
Figure 3
MOZART-4 simulation results with the inclusion of O3 + PM at the reaction probability γO3 0.001; see the
Supporting Information
for the results with reduced γO3. (Top) The annually averaged heterogeneous reaction rate (μgC/m3/day) that oxidizes PM to CO2, compared to a typical ∼10–100 μg/m3 PM loading in the polluted atmosphere. (Middle) The annually averaged surface O3 concentration (ppb). (Bottom) The annually averaged surface O3 concentration (ppb) from the standard model. (The figures are made using the GEOV geophysical visualization tool. Copyright: University Corporation for Atmospheric Research and Max Planck Institute for Meteorology, Hamburg.)
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