Oxidation of Catechols at the Air-Water Interface by Nitrate Radicals.

Authors

Md. Sohel Rana, USDA
Marcelo I. Guzman, University of Kentucky

Abstract

Abundant substituted catechols are emitted to, and created in, the atmosphere during wildfires and anthropogenic combustion and agro-industrial processes. While ozone (O₃) and hydroxyl radicals (HO^•) efficiently react in a 1 μs contact time with catechols at the air–water interface, the nighttime reactivity dominated by nitrate radicals (NO₃) remains unexplored. Herein, online electrospray ionization mass spectrometry (OESI-MS) is used to explore the reaction of NO₃(g) with a series of representative catechols (catechol, pyrogallol, 3-methylcatechol, 4-methylcatechol, and 3-methoxycatechol) on the surface of aqueous microdroplets. The work detects the ultrafast generation of nitrocatechol (aromatic) compounds, which are major constituents of atmospheric brown carbon. Two mechanisms are proposed to produce nitrocatechols, one (equivalent to H atom abstraction) following fast electron transfer from the catechols (QH₂) to NO₃, forming NO₃^– and QH₂^•+ that quickly deprotonates into a semiquinone radical (QH^•). The second mechanism proceeds via cyclohexadienyl radical intermediates from NO₃ attack to the ring. Experiments in the pH range from 4 to 8 showed that the production of nitrocatechols was favored under the most acidic conditions. Mechanistically, the results explain the interfacial production of chromophoric nitrocatechols that modify the absorption properties of tropospheric particles, making them more susceptible to photooxidation, and alter the Earth’s radiative forcing.

Document Type

Article

Publication Date

11-1-2022

Notes/Citation Information

Published in Environmental Science and Technology v. 56, issue (22):p. 15437-15448

Digital Object Identifier (DOI)

10.1021/acs.est.2c05640

Funding Information

Funding from the USA National Science Foundation under award 1903744 to M.I.G. is greatly acknowledged.

Repository Citation

Rana, Md. Sohel and Guzman, Marcelo I., "Oxidation of Catechols at the Air-Water Interface by Nitrate Radicals." (2022). Chemistry Faculty Publications. 198.
https://uknowledge.uky.edu/chemistry_facpub/198