Photoformation of OH radical in water-extract of atmospheric aerosols and aqueous solution of water-soluble gases collected in Higashi-Hiroshima, Japan

Abstract

Chemical composition, hydroxyl radical (•OH) photoformation rate (R OH ) and primary generation sources of •OH in water-extract of aerosol (WEA) and aqueous solution of water-soluble gases (WSG) in the atmosphere were studied at Higashi-Hiroshima, Japan from June 2008 to June 2010. Among the major anions present in the WSG samples, the SO 4 2-concentration was highest (9.4 ± 4.0 nmol m -3 ), followed by NO 3 -and Cl -, while the mean concentration of SO 4 2-in the WEA fraction was 81 ± 33 nmol m -3 . The initial concentrations of H 2 O 2 were 0.2 ± 0.3 and 0.9 ± 2.3 nmol m -3 in the WSG and WEA, respectively. The extracted sample was irradiated using a solar simulator, after which the R OH was determined and normalized against the sun-light intensity of a clear sky midday on May 1 at 34°N, which revealed values of 1.4 and 0.5 nmol h -1 m -3 for the WEA and WSG, respectively. The contribution of NO 3 -, NO 2 -and H 2 O 2 to the formation of •OH via photolysis was 4.5, 0.7 and 1.2%, respectively, for the WSG fraction, while in the WEA fraction, the contribution was 8.9, 1.2 and 2.5%, respectively. Other contribution sources of •OH could include the photo-Fenton reaction and fluorescent matter such as humic-like substances (HULIS). The photo-Fenton reaction was estimated to potentially contribute up to 42% of the total •OH formation in the WSG fraction, while the fluorescent matter may account for the remaining 52%.

Reactive Uptake and Photo-Fenton Oxidation of Glycolaldehyde in Aerosol Liquid Water

“…Fenton and photo-Fenton are redox reactions of iron (Fe (II)/ Fe (III) ) with H 2 O 2 , producing aqueous OH and other oxidizing agents in either the dark or photolytic conditions, respectively. Fenton mechanisms are powerful in the bulk cloudwater-phase application, − and are often utilized for wastewater treatment of organic pollutants; , however, they have yet to be demonstrated as OH sources in the liquid water of suspended aerosol.…”

Aqueous Radical Initiated Oxidation of an Organic Monolayer at the Air–Water Interface as a Proxy for Thin Films on Atmospheric Aerosol Studied with Neutron Reflectometry

“…It is known that aqueous cloud processes oxidize thin films, but little is known about the kinetics. Therefore, in order to assess the importance of aqueous-phase oxidation of thin films and to determine the film lifetime with respect to oxidation, the investigation of the aqueous phase oxidation of a well-defined organic film of the lipid 1,2-distearoyl- sn -glycero-3-phosphocholine (DSPC) by the common cloudwater aqueous phase radicals, hydroxyl ( • OH), − sulfate (SO 4 •– ) , and nitrate (NO 3 • ), ,, was performed. The reactions were probed by a series of neutron reflectometry experiments using films spread on the surface of solutions in a Teflon trough.…”