Environmental Photochemistry in Heterogeneous Media

Review of the bulk and surface chemistry of iron in atmospherically relevant systems containing humic-like substances

“…Interest in the iron-driven aqueous phase photosensitized degradation of organic compounds is driven mainly by the desire to treat wastewater contaminated by soluble natural organic matter and phenolic compounds produced from the decay of plants or the food and pigment industries. 102,103,105 This chemistry can also be used to explain homogeneous reactions in cloud droplets 41 and atmospheric organic aerosols. 106 In this photochemistry, Fenton reagents, such as Fe(II) and H 2 O 2 , are most commonly used as efficient producers of cOH radicals (reaction ( 5)).…”

“…26 This means that, depending on the size and water content of the particles, preferential partitioning of HULIS to the surface could become important in their overall surface reactivity. Although bulk photochemical reactions involving humic substances in atmospheric aerosols and aquatic systems have received much attention, 13,14,[39][40][41] fewer studies have reported the heterogeneous photochemistry of atmospheric HULIS. Examples include: (a) the fast photosensitized formation of HONO from the photoreaction of NO 2 with humic, 42,43 tannic and gentisic acid lms 28 under dry and humid conditions; (b) the photooxidation, formation and characterization of secondary particles from catechol and guaiacol; 23 and (c) changes to the functional groups characteristic of solid tannic acid and the formation of new carbonyl groups characteristic of aryl aldehydes and/or quinone under humid conditions.…”

“…[47][48][49][50][51] This latter pathway could be driven by the electronically excited states of some organic chromophores such as HULIS or by soluble and insoluble transition metals such as iron. 14 In addition to inuencing the oxidative power of the atmosphere and the global sulfate budget, 41,52 particulate iron can catalyse reactions that lead to oxidative stress in living cells as a result of the production of reactive oxygen species (ROS). 53 Dark and photochemical processes that lead to the release of soluble iron into the aqueous phase have consequences for the availability of this essential element for phytoplankton productivity, the extent of algal blooms and the uptake of atmospheric CO 2 .…”

Reactions of Cl•/Cl2•− Radicals with the Nanoparticle Silica Surface and with Humic Acids: Model Reactions for the Aqueous Phase Chemistry of the Atmosphere

“…In order to further prove the proposed reaction mechanism, a computer program was used to simulate the experimental absorbance profiles at 340 nm. To this purpose, reactions (1-3) and (5)(6)(7)(8)(9)(10)(11), along with the reactions of SO 4…”

“…In this study, we report a kinetic and mechanistic study on the aqueous phase reactions of Cl • and Cl 2 •− radicals with colloidal silica nanoparticles (NP) and Aldrich humic acids (HA) solutions. Highly polar surfaces such as those of silica serve as models for the inorganic solid components of particulate matter (9), and as a first approximation, commercial humic acids (HA) are used as models of HULIS. In situ generation of Cl • and Cl 2 •− is performed by conventional flash photolysis of S 2 O 8 2− in the presence of various concentrations of chloride ions.…”