Abstract
Criegee intermediates are reactive intermediates that are implicated in transforming the composition of Earth’s troposphere and in the formation of secondary organic aerosol, impacting Earth’s radiation balance, air quality and human health. Yet, direct identification of their signatures in the field remains elusive. Here, from particulate and gas-phase mass-spectrometric measurements in the Amazon rainforest, we identify sequences of masses consistent with the expected signatures of oligomerization of the CH2OO Criegee intermediate, a process implicated in ozonolysis-driven aerosol formation. We assess the potential contributions of oligomerization through laboratory ozonolysis experiments, direct kinetic studies of Criegee intermediate reactions, and high-level theoretical calculations. Global atmospheric models built on these kinetics results indicate that Criegee intermediate chemistry may play a larger role in altering the composition of Earth’s troposphere than is captured in current atmospheric models, especially in areas of high humidity. However, the models still capture only a relatively small fraction of the observed signatures, suggesting considerable underestimates of Criegee intermediate concentrations and reactivity and/or the dominance of other, presently uncharacterized, oxidation mechanisms. Resolving the remaining uncertainties in emission inventories and the effects of atmospheric water vapour on key chemical reactions will be required to definitively assess the role of Criegee intermediate oligomerization reactions.
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Data availability
The data supporting the findings of this study are shown as figures or tables available in the main text or Supplementary Information, and are available alongside the master equation input and output files at https://doi.org/10.5281/zenodo.10267863.
Code availability
The codes used for the theoretical kinetics work are available at https://tcg.cse.anl.gov/papr/, https://github.com/auto-mech, https://comp.chem.umn.edu/dint/ and https://github.com/Auto-Mech/PIPPy, or are commercially available. The codes used for the atmospheric modelling work are available at https://github.com/chmahk/stochem.
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Acknowledgements
We gratefully acknowledge K. Au, R. Almeida and P. Fugazzi for technical assistance with the MPIMS and JSR experiments. We are grateful to A. J. Eskola, J. D. Savee, O. Welz, M.-W. Chen and I. O. Antonov for early MPIMS attempts. We thank S. Carbone for maintaining the ozone, NOx and ACSM instruments during the field campaign, and the LBA central office at INPA in Manaus for field support. We are grateful to R. P. Evershed, A. J. Orr-Ewing, S. T. Pratt, S. P. Sander, L. Young and J. Zádor for useful discussions. This material is based on work supported by the Division of Chemical Sciences, Geosciences and Biosciences, Office of Basic Energy Sciences (BES), US Department of Energy (USDOE; R.L.C., A.C.R., A.W.J., D.L.O., N.H., S.J.K. and C.A.T.). Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for USDOE’s National Nuclear Security Administration under contract DE-NA0003525. Argonne National Laboratory is supported by the USDOE, Office of Science, BES, Division of Chemical Sciences, Geosciences, and Biosciences under contract no. DE-AC02-06CH11357. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. The contributions of R.L.C. were in part supported by an appointment to the National Aeronautics and Space Administration (NASA) Postdoctoral Program at the NASA Jet Propulsion Laboratory, administered by the Universities Space Research Association under contract with NASA. This research was carried out in part by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the NASA, supported by the Upper Atmosphere Research and Tropospheric Chemistry program (F.A.F.W. and C.J.P). D.E.S. and M.A.H.K. were supported by NERC (NE/K004905/1), the Primary Science Teaching Trust and Bristol ChemLabS. The fieldwork was supported by the FAPESP-University of Manchester SPRINT initiative (T.J.B., S.D.W., A.B., M.P., J.D.A., H.C. and C.J.P.). P.A. acknowledges funding from FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, 2017/17047-0 and 2023/04358-9). Y.J. was partly supported by grants from the DOE Plasma Science Center (DE-SC0020233), DOE BES (DE-AC0209CH11466), and the National Science Foundation (NSF-EFRI CBET-2029425). IMT Nord Europe (J.B.) acknowledges financial support from the Labex CaPPA project, funded by the French National Research Agency (ANR, contract ANR-11-LABX-0005-01) and the CPER ECRIN, financed by the Regional Council ‘Hauts-de-France’ and the European Regional Development Fund (ERDF). This Article describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the Article do not necessarily represent the views of the USDOE or the United States Government. The Sandia authors own all right, title, and interests in and to the article and are solely responsible for its contents. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this article or allow others to do so, for United States Government purposes. The DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan https://www.energy.gov/downloads/doe-public-access-plan.
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Conceptualization was provided by R.L.C., P.A., N.H., S.J.K., D.E.S., C.A.T. and C.J.P. Methodology was provided by F.A.F.W., M.A.H.K., A.W.J., Y.J., D.L.O., N.H., S.J.K., D.E.S., C.A.T. and C.J.P. Software was provided by F.A.F.W., M.A.H.K., A.W.J., D.L.O., S.J.K., D.E.S. and C.A.T. Validation was performed by R.L.C., T.J.B., F.A.F.W., P.A. and J.B. Formal analysis was carried out by R.L.C., T.J.B., F.A.F.W., M.A.H.K., A.W.J., S.D.W., N.H. and S.J.K. Investigations were carried out by R.L.C., T.J.B., F.A.F.W., M.A.H.K., A.C.R., A.W.J., M.P., N.H., S.J.K., D.E.S., C.A.T. and C.J.P. Resources were provided by F.A.F.W., A.C.R., A.W.J., M.P., D.L.O., N.H., S.J.K., D.E.S., C.A.T. and C.J.P. Data curation was carried out by R.L.C., T.J.B., F.A.F.W., M.A.H.K., A.C.R., A.W.J., S.D.W., J.B., N.H. and S.J.K. The original draft was written by R.L.C., T.J.B., F.A.F.W., M.A.H.K., N.H., S.J.K., D.E.S., C.A.T. and C.J.P. Review and editing was carried out by R.L.C., T.J.B., F.A.F.W., M.A.H.K., A.C.R., A.W.J., S.D.W., A.B., P.A., J.B., M.P., J.D.A., H.C., Y.J., D.L.O., N.H., S.J.K., D.E.S., C.A.T. and C.J.P. Visualization was provided by R.L.C., T.J.B., F.A.F.W., M.A.H.K. and S.J.K. Supervision was provided by R.L.C., J.D.A., Y.J., N.H., D.E.S., C.A.T. and C.J.P. Project administration was provided by R.L.C., P.A., J.D.A., D.L.O., N.H., S.J.K., D.E.S., C.A.T. and C.J.P. Funding acquisition was performed by R.L.C., A.W.J., P.A., J.D.A., H.C., Y.J., D.L.O., N.H., S.J.K., D.E.S., C.A.T. and C.J.P.
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Extended data
Extended Data Fig. 1 Complete time series of various measured species over the Amazon rainforest.
Complete time series from the 23rd June through 6th July 2015 of: (Upper) NO2 (grey), ozone (blue), isoprene (green). (Middle) Formic acid (grey) and gas-phase insertion products from n = 2–7. (Lower) particle-phase insertion products from n = 3–6. Note that missing TOF-CIMS data on the 30th June 2015 is a result of a power failure.
Extended Data Fig. 2 Average (mean) diurnal profiles of various species measured in our Amazon field measurements.
(Upper) Major precursors of our proposed insertion sequence: isoprene, formic acid, and ozone (scaled down for ease of comparison). (Middle) Isoprene, the n = 2 insertion product from our oligomerization sequence, and IEPOX (scaled down for ease of comparison, C5H10O3), a 2nd generation product of isoprene oxidation. (Lower) Formic acid (scaled down for ease of comparison), and the n = 1–6 insertion products resulting from sequential insertion of CH2OO into formic acid. The high background signal on the mass of the n = 1 insertion product precluded reliable extraction of its diurnal profile and analysis of its origin. Thus, this data is not presented in the main text and not discussed further in the manuscript. The diel patterns of IEPOX, a second-generation isoprene oxidation product, and of our insertion products are similar and indicative of a marker of a photochemical oxidation product. As indicated in the figure legends, the amplitudes of some species (for example, formic acid) have been scaled for ease of comparison of the species time profiles.
Extended Data Fig. 3 Correlation between the n = 4 product in the aerosol phase and its precursors.
Positive correlation between the integrated area of the n = 4 product (m/z 356.9 = C5H10O10 bound to I−) in the aerosol phase and the total measured organics, measured via ACSM and FIGAERO-CIMS respectively. The abundance of m/z 356.9 (=C5H10O10 bound to I−) is linked with the concentration of isoprene by the colour scale. The size of the circles is proportional to formic acid concentration. Data presented are the mean of measurements throughout the entire campaign. The correlation between the n = 4 abundance in the aerosol phase and critical gas-phase precursors suggests that sCI chemistry plays a central role in the generation of this sequence. In the aerosol phase, the integrated signal at the exact mass of the n = 4 product increases linearly with the total concentration of organic species measured via an aerosol chemical speciation monitor (ACSM). The abundance is moderately correlated with the gas-phase concentration of isoprene: other non-isoprene biogenic terminal alkenes can also produce CH2OO that leads to the formation of these highly oxygenated compounds, and their eventual partitioning into the aerosol-phase.
Extended Data Fig. 4 Pressure dependence of the rate coefficient for CH2OO + H2O2.
Plot of the pressure dependence of the theoretically predicted rate coefficients for the reaction of CH2OO with H2O2. The rates were calculated for room temperature. The symbol denotes the experimental data from the present study.
Extended Data Fig. 5 Temperature dependence of the rate coefficient for CH2OO + H2O2.
Plot of the temperature dependence of the theoretically predicted rate coefficients for the reaction of CH2OO with H2O2. The rates were calculated for 1 Bar of He. The lines are labelled according to their products, with the eff label corresponding to the effective rate coefficient obtained by summing the direct contributions with the contributions from the rapid decay of the initially formed CH2OO…H2O2 van der Waals complex.
Extended Data Fig. 6 Pressure and temperature dependence of the rate coefficient for CH2OO + HPMF.
Plot of the temperature and pressure dependence of the theoretically predicted rate coefficients for the stabilization of the vdW complex (dashed lines) and for the overall reaction of HPMF with CH2OO (solid lines). In these calculations, the bath gas is taken to be Ar, which is used as a surrogate for air. The pressures are as denoted in the legend, in units of bar.
Extended Data Fig. 7 Temperature dependence of the rate coefficient for CH2OO + HPMF.
Plot of the temperature dependence of the theoretically predicted rate coefficients for the reaction of HPMF with CH2OO at 1 bar of Ar, which is used as a surrogate for air.
Extended Data Fig. 8 Modelled total sCI concentration.
Modelled total sCI concentration after expanding the alkene inventory.
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Supplementary Notes 1–6, Figs. 1–28, Tables 1–12 and References.
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Caravan, R.L., Bannan, T.J., Winiberg, F.A.F. et al. Observational evidence for Criegee intermediate oligomerization reactions relevant to aerosol formation in the troposphere. Nat. Geosci. 17, 219–226 (2024). https://doi.org/10.1038/s41561-023-01361-6
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DOI: https://doi.org/10.1038/s41561-023-01361-6