Photochemistry of Atmospheric Iodine Oxide Clusters

The formation of climatically relevant particles from trace vapors in the atmosphere is a significant source of aerosol. The chemistry driving this process in the present-day and pre-industrial atmospheres remains poorly characterized, particularly in the critical sub-10 nm size range, in no small part due to a dearth of analytical techniques capable of delivering chemical insight into particles of this size. My group develops laboratory techniques that can be used as precision tests of these efforts, probing the structures, thermodynamics, and kinetics of newly formed particles with exact atomic precision. I will discuss our work to test the basic assumptions of these models, the still-unclear role of water in particle formation, and the potential (but currently largely ignored) influence of photochemistry on the growth of iodine oxide particles, which are potentially important in coastal and polar regions. We find that UV photolysis in atmospherically relevant wavelength ranges occurs at rates that compete with particle growth and scale with the number of iodine oxide species in the particle. We observe a previously unknown channel leading to production of oxygen atoms and triplets that may initiate intraparticle chemistry.