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UVA/Vis-induced nitrous acid formation on polyphenolic films exposed to gaseous NO2.

Authors
  • 1
  • 1 Paul Scherrer Institute, 5232 Villigen PSI, Switzerland. [email protected] , (Switzerland)
Type
Published Article
Journal
Photochemical & Photobiological Sciences
1474-9092
Publisher
The Royal Society of Chemistry
Publication Date
Volume
10
Issue
10
Pages
1680–1690
Identifiers
DOI: 10.1039/c1pp05113j
PMID: 21811730
Source
Medline
License
Unknown

Abstract

Photochemical processes on ground and airborne surfaces have been suspected to lead to production of HONO in the sunlit lower troposphere, e.g. upon light activation of humic acids followed by reaction with adsorbed NO(2). Here, we used tannic and gentisic acids as proxies for atmospheric polyphenolic compounds to obtain further insights into the photoenhanced NO(2) conversion to HONO, which is a significant tropospheric hydroxyl radical (OH) source. The coated wall flow tube technique was used in combination with online detection of gas-phase HONO and NO(x) under different irradiation conditions. Photoenhanced HONO formation rates of 0.1 to 2 ppbv s(-1) were measured upon NO(2) (0-400 ppbv) uptake on tannic and gentisic acid coatings under irradiation with UV light. The data allow identification of three pathways of light-induced HONO formation: (I) photolysis of a nitroaromatic intermediate formed by a non-photochemical process in the dark, with a photolysis frequency of 10(4) s(-1) at 2 × 10(20) photons m(-2) photon flux; (II) direct photo-oxidation, presumably through electron or hydrogen transfer of the excited substrate; and (III) sensitized electron or hydrogen transfer as suggested before but also demonstrated for visible irradiation here. Aging of tannic acid under oxygen in the dark led to products which promoted light-induced HONO formation in the visible.

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