The photochemical reactions of various I x O y have been probed in several studies recently. In one study, the authors combined pulsed photolysis, photodepletion and photoionization TOFMS (PI-TOFMS).( ) IO, produced in situ by the reaction between triplet oxygen and iodine, underwent further reactions to form larger I x O y . The photodepletion of these I x O y species was carried out at 355 and 532 nm and products were detected by PI-TOFMS. IO and I 2 O 4 showed significant depletion at 355 nm, with sufficiently large photolysis cross sections suggesting that these species are not likely to participate in particle growth. The photolytic lifetimes of different I x O y species suggest that photolysis of more photolabile species such I 3 O 7 and I 5 O 12 is likely to slow down particle formation while less photolabile species are likely to be contribute more to particle growth in the atmosphere. Another study probed the UV photodissociation of (I 2 O 5 ) 0-3 (IO 3 -) clusters and found that loss of O atom, I 2 O 4 and I 2 O 5 were the major photofragmentation pathways in the actinic region.(122) Loss of I 2 O 5 was found to be much faster than the loss of O, with estimated rates indicating that photolysis of these clusters is likely to compete with particle formation under ambient conditions. The O-loss fragment likely left behind a triplet cluster that could then undergo further complex reactions with other particle constituents such as organics and amines.