The heterogeneous reaction of volatile organic compounds (VOCs) with excited triplet photosensitizers adsorbed to aerosol particle surfaces represents a photochemical pathway to secondary organic aerosol (SOA) growth.  We examine the kinetics of the initial stages of this chemistry and their dependence on particle morphology by measuring the lifetime of the triplet excited state.    We use an atmospheric pressure laser photoionization scheme to monitor the triplet state wherein one laser pulse generates the excited triplet and another pulse selectively ionizes the excited molecules.  Measuring the photoionization signal as a function the delay between the lasers yields the lifetime of the triplet state.  This lifetime for the model photosensitizer, 2-acetonaphthone (2-AN), in the absence of VOCs, depends strongly on the composition of the particles and ranges from 10-200 ns for the systems we studied.   Iodide is the most effective quencher studied to date.  Transients measured with α-pinene included in the flow system show both the decay of the triplet and the fast rise of a signal we attribute to reaction products.  The results suggest that the reaction of surface adsorbed α-pinene plays an important role in photochemical SOA formation.

LIfetime of photosensizer triplet states in model troposheric aerosol

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.