Photochemistry of the Cloud Aqueous Phase: A Review

Abstract

This review paper describes briefly the cloud aqueous phase composition and deeply its reactivity in the dark and mainly under solar radiation. The role of the main oxidants (hydrogen peroxide, nitrate radical, and hydroxyl radical) is presented with a focus on the hydroxyl radical, which drives the oxidation capacity during the day. Its sources in the aqueous phase, mainly through photochemical mechanisms with H2O2, iron complexes, or nitrate/nitrite ions, are presented in detail. The formation rate of hydroxyl radical and its steady state concentration evaluated by different authors are listed and compared. Finally, a paragraph is also dedicated to the sinks and the reactivity of the HO• radical with the main compounds found in the cloud aqueous phase. This review presents an assessment of the reactivity in the cloud aqueous phase and shows the significant potential impact that this medium can have on the chemistry of the atmosphere and more generally on the climate.

Secondary Formation of Aromatic Nitroderivatives of Environmental Concern: Photonitration Processes Triggered by the Photolysis of Nitrate and Nitrite Ions in Aqueous Solution

“…where Φ is the quantum yield of nitrate photolysis (ratio between photolysed molecules and absorbed photons). The two photogenerated fragments are initially located inside a cage of water molecules, where three alternative processes can take place [23,33] Geminate recombination of the two fragments back to the original NO 3 − ; and 3.…”

Photochemical degradation of iron(III) citrate/citric acid aerosol quantified with the combination of three complementary experimental techniques and a kinetic process model

“…2 self-reaction rate, k 5 , which was adjusted to match observations in panel (a) (black dots), or times k 5 parameterized as a function of RH for our PRAD model (Eq. A11) with confidence interval of 95 % (red line and shading), or times k 5 from Corral Arroyo et al ( 2018) (dotted blue line), or k 5 = 8.3 × 10 5 M −1 s −1 (Bielski et al, 1985) (dashed blue line). creased from 13 % to 29 % by a factor of about 2.…”

“…2 self-reaction rate of k 5 = 8.5×10 −5 M −1 s −1 (Bielski et al, 1985) or a linearly increasing P HO .…”

“…R−COO . will decarboxylate almost instantaneously (k R3 ≈ 10 9 -10 12 s −1 ) (Abel et al, 2003;Bockman et al, 1997;Hilborn and Pincock, 1991):…”

“…2 production from continued photochemistry of Fe III (Cit) / CA (molar ratio of 0.07) films as a function of RH in CWFT experiments. Dotted and dashed blue lines were determined from parameterization of k 5 as a function of RH (Corral Arroyo et al, 2018) and k 5 = 8.3 × 10 5 M −1 s −1 in dilute aqueous solution(Bielski et al, 1985), respectively. (b) The maximum HO .2 first-order loss rate determined from the result of the maximum HO .2 concentration times HO .2 self-reaction rate, k 5 , which was adjusted to match observations in panel (a) (black dots), or times k 5 parameterized as a function of RH for our PRAD model (Eq.…”