Large quantities of mineral dust particles are frequently ejected into the atmosphere through the action of wind. The surface of dust particles acts as a sink for many gases, such as sulfur dioxide. It is well known that under most conditions, sulfur dioxide reacts on dust particle surfaces, leading to the production of sulfate ions. In this report, for specific atmospheric conditions, we provide evidence for an alternate pathway in which a series of reactions under solar UV light produces first gaseous sulfuric acid as an intermediate product before surface-bound sulfate. Metal oxides present in mineral dust act as atmospheric photocatalysts promoting the formation of gaseous OH radicals, which initiate the conversion of SO
2
to H
2
SO
4
in the vicinity of dust particles. Under low dust conditions, this process may lead to nucleation events in the atmosphere. The laboratory findings are supported by recent field observations near Beijing, China, and Lyon, France.
We report on experiments that probe
photosensitized chemistry at
the air/water interface, a region that does not just connect the two
phases but displays its own specific chemistry. Here, we follow reactions
of octanol, a proxy for environmentally relevant soluble surfactants,
initiated by an attack by triplet-state carbonyl compounds, which
are themselves concentrated at the interface by the presence of this
surfactant. Gas-phase products are determined using PTR-ToF-MS, and
those remaining in the organic layer are determined by ATR-FTIR spectroscopy
and HPLC-HRMS. We observe the photosensitized production of carboxylic
acids as well as unsaturated and branched-chain oxygenated products,
compounds that act as organic aerosol precursors and had been thought
to be produced solely by biological activity. A mechanism that is
consistent with the observations is detailed here, and the energetics
of several key reactions are calculated using quantum chemical methods.
The results suggest that the concentrating nature of the interface
leads to its being a favorable venue for radical reactions yielding
complex and functionalized products that themselves could initiate
further secondary chemistry and new particle formation in the atmospheric
environment.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.