Photochemistry of 2-butenedial and 4-oxo-2-pentenal under atmospheric boundary layer conditions

Newland, Mike J.; Rea, Gerard J.; Thüner, Lars P.; Henderson, Alistair P.; Golding, Bernard T.; Rickard, Andrew R.; Barnes, Ian; Wenger, John

Photochemistry of 2-butenedial and 4-oxo-2-pentenal under atmospheric boundary layer conditions

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c8cp06437g1.pdf(2.67 MB)

Supplementary Information

Date

2018-12-21

Authors

Newland, Mike J.

Rea, Gerard J.

Thüner, Lars P.

Henderson, Alistair P.

Golding, Bernard T.

Rickard, Andrew R.

Barnes, Ian

Wenger, John

Publisher

Royal Society of Chemistry

Published Version

https://doi.org/10.1039/C8CP06437G

Abstract

Unsaturated 1,4-dicarbonyl compounds, such as 2-butenedial and 4-oxo-2-pentenal are produced in the atmospheric boundary layer from the oxidation of aromatic compounds and furans. These species are expected to undergo rapid photochemical processing, affecting atmospheric composition. In this study, the photochemistry of (E)-2-butenedial and both E and Z isomers of 4-oxo-2-pentenal was investigated under natural sunlight conditions at the large outdoor atmospheric simulation chamber EUPHORE. Photochemical loss rates, relative to j(NO2), are determined to be j((E)-2-butenedial)/j(NO2) = 0.14 (±0.02), j((E)-4-oxo-2-pentenal)/j(NO2) = 0.18 (±0.01), and j((Z)-4-oxo-2-pentenal)/j(NO2) = 0.20 (±0.03). The major products detected for both species are a furanone (30–42%) and, for (E)-2-butenedial, maleic anhydride (2,5-furandione) (12–14%). The mechanism appears to proceed predominantly via photoisomerization to a ketene–enol species following γ-H abstraction. The lifetimes of the ketene–enol species in the dark from 2-butenedial and 4-oxo-2-pentenal are determined to be 465 s and 235 s, respectively. The ketene–enol can undergo ring closure to yield the corresponding furanone, or further unimolecular rearrangement which can subsequently form maleic anhydride. A minor channel (10–15%) also appears to form CO directly. This is presumed to be via a molecular elimination route of an initial biradical intermediate formed in photolysis, with an unsaturated carbonyl (detected here but not quantified) as co-product. α-Dicarbonyl and radical yields are very low, which has implications for ozone production from the photo-oxidation of unsaturated 1,4-dicarbonyls in the boundary layer. Photochemical removal is determined to be the major loss process for these species in the boundary layer with lifetimes of the order of 10–15 minutes, compared to >3 hours for reaction with OH.

Keywords

2-butenedial and 4-oxo-2-pentenal , Atmospheric boundary layer conditions , Photochemistry

Citation

Newland, M. J., Rea, G. J., Thüner, L. P., Henderson, A. P., Golding, B. T., Rickard, A. R., Barnes, I. and Wenger, J. (2019) 'Photochemistry of 2-butenedial and 4-oxo-2-pentenal under atmospheric boundary layer conditions', Physical Chemistry Chemical Physics, 2(3), pp.1160-1171. Available at: https://doi.org/10.1039/C8CP06437G