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Ocean emissions of inorganic and organic iodine compounds drive the biogeochemical cycle of iodine and produce reactive ozone-destroying iodine radicals that influence the oxidizing capacity of the atmosphere. Di-iodomethane (CH 2 I 2 ) and chloro-iodomethane (CH 2 ICl) are the two most important organic iodine precursors in the marine boundary layer. Ship-borne measurements made during the TORERO (Tropical Ocean tRoposphere Exchange of Reactive halogens and Oxygenated VOC) field campaign in the east tropical Pacific Ocean in January/February 2012 revealed strong diurnal cycles of CH 2 I 2 and CH 2 ICl in air and of CH 2 I 2 in seawater. Both compounds are known to undergo rapid photolysis during the day, but models assume no night-time atmospheric losses. Surprisingly, the diurnal cycle of CH 2 I 2 was lower in amplitude than that of CH 2 ICl, despite its faster photolysis rate. We speculate that night-time loss of CH 2 I 2 occurs due to reaction with NO 3 radicals. Indirect results from a laboratory study under ambient atmospheric boundary layer conditions indicate a k CH2I2+NO3 of ≤4 × 10 −13 cm 3 molecule −1 s −1 ; a previous kinetic study carried out at ≤100 Torr found k CH2I2+NO3 of 4 × 10 −13 cm 3 molecule −1 s −1 . Using the 1-dimensional atmospheric THAMO model driven by sea-air fluxes calculated from the seawater and air measurements (averaging 1.8 +/− 0.8 nmol m −2 d −1 for CH 2 I 2 and 3.7 +/− 0.8 nmol m −2 d −1 for CH 2 ICl), we show that J Atmos Chem (2017)