From these results we can draw some broader inferences about the role of photochemistry in laboratory and ambient NPF studies. First, it is clear that the photoproducts resulting from UV absorption will depend substantially on the power spectrum of the excitation light source, particularly in the region near 300 nm where these clusters begin to absorb significantly. Narrowband laser-like sources, particularly deeper in the non-atmosphericallyrelevant UV region, may drive non-atmospherically-relevant relative yields of photofragments. Even broadband light sources that do not closely mirror the solar spectrum may induce significant deviations from the ambient abundances of similar clusters due to the sharp turn on of absorption near the atmospheric window. Promotion of the O loss fragmentation channel, in particular, will change the chemical composition of the particle, namely the I:O ratio, while loss of I 2 O 5 can be viewed more simply as suppressing growth. Second, even for new particles of only a few nanometers in relatively pristine environments, particle composition is likely to include bases or organics. The fact that fragmentation can yield 3 O atoms and 3 (cluster) suggests that photoinduced intraparticle chemistry may be common and may play an important role in the fate of new particles containing iodine. Finally, coupling between organic and iodine oxide/iodic acid components of new particles may qualitatively perturb their spectra, borrowing intensity from the strong absorption of the iodine oxides but red shifting their spectra further into the atmospherically relevant range. In this case, the role of photochemistry in new particle evolution would likely be even more pronounced.