Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NOₓ from the atmosphere
Abstract
The formation of a suite of isoprene-derived hydroxy nitrate (IHN) isomers during the OH-initiated oxidation of isoprene affects both the concentration and distribution of nitrogen oxide free radicals (NOₓ). Experiments performed in an atmospheric simulation chamber suggest that the lifetime of the most abundant isomer, 1,2-IHN, is shortened significantly by a water-mediated process (leading to nitric acid formation), while the lifetime of a similar isomer, 4,3-IHN, is not. Consistent with these chamber studies, NMR kinetic experiments constrain the 1,2-IHN hydrolysis lifetime to less than 10 s in deuterium oxide (D₂O) at 298 K, whereas the 4,3-IHN isomer has been observed to hydrolyze much less efficiently. These laboratory findings are used to interpret observations of the IHN isomer distribution in ambient air. The IHN isomer ratio (1,2-IHN to 4,3-IHN) in a high NOₓ environment decreases rapidly in the afternoon, which is not explained using known gas-phase chemistry. When simulated with an observationally constrained model, we find that an additional loss process for the 1,2-IHN isomer with a time constant of about 6 h best explains our atmospheric measurements. Using estimates for 1,2-IHN Henry's law constant and atmospheric liquid water volume, we show that condensed-phase hydrolysis of 1,2-IHN can account for this loss process. Simulations from a global chemistry transport model show that the hydrolysis of 1,2-IHN accounts for a substantial fraction of NOₓ lost (and HNO₃ produced), resulting in large impacts on oxidant formation, especially over forested regions.
Additional Information
© 2020 Published under the PNAS license. Edited by Mark Thiemens, University of California San Diego, La Jolla, CA, and approved November 3, 2020 (received for review August 17, 2020). First published December 10, 2020. Development of the GC-CIMS was supported by the NSF Major Research Instrumentation Program under Grant AGS-1428482 and the field and laboratory studies it participated in were supported by additional NSF funding (Grant AGS-1240604). We thank the Caltech campus and affiliated staff for accommodating our 2017 field study. Work performed by K.T.V. and H.M.A. was also supported by NSF through the Graduate Research Fellowship. Author contributions: J.D.C. and P.O.W. designed research; K.T.V., J.D.C., B.C.S., K.H.B., A.P.T., L.X., H.M.A., and P.O.W. performed research; J.D.C. and P.O.W. contributed new reagents/analytic tools; K.T.V., J.D.C., and A.P.T. analyzed data; and K.T.V., J.D.C., and P.O.W. wrote the paper. Data Availability. Atmospheric trace gas measurements and model output data have been deposited in the California Institute of Technology Research Data Repository CaltechDATA. IHN isomer concentration data used here are available online (http://doi.org/10.22002/D1.971) along with the chromatograms collected at the field site (http://doi.org/10.22002/D1.1671), the output results of the 1-D atmospheric model (http://doi.org/10.22002/D1.1672), and the updated isoprene mechanism used in the global chemical transport model (http://doi.org/10.22002/D1.247). GEOS-Chem is available for public use at http://geos-chem.org/. The authors declare no competing interest. This article is a PNAS Direct Submission. This article contains supporting information online at https://www.pnas.org/lookup/suppl/doi:10.1073/pnas.2017442117/-/DCSupplemental.Attached Files
Published - 33011.full.pdf
Supplemental Material - pnas.2017442117.sapp.pdf
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Additional details
- Alternative title
- Rapid hydrolysis of tertiary isoprene nitrate efficiently removes NOx from the atmosphere
- PMCID
- PMC7777079
- Eprint ID
- 107029
- Resolver ID
- CaltechAUTHORS:20201210-160240365
- AGS-1428482
- NSF
- AGS-1240604
- NSF
- NSF Graduate Research Fellowship
- Created
-
2020-12-11Created from EPrint's datestamp field
- Updated
-
2023-07-18Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences