Mounting evidence suggests that Criegee intermediates are important tropospheric oxidants of both organic and inorganic gases, supplementing the oxidation chemistry initiated by OH radicals. Here, the rate coefficient for the reaction of the simplest Criegee intermediate CH₂OO with acetone, k(CH₂OO + (CH₃)₂CO), was measured using laser flash photolysis and cavity ring-down spectroscopy methods under tropospherically relevant conditions of pressure and temperature. The pressure dependence of k(CH₂OO + (CH₃)₂CO) = (4.7 ± 0.1) × 10^–13 [N₂]/((3.7 ± 1.4) × 10¹⁶ + [N₂]) cm³ molecule^–1 s^–1 was measured in the 5–100 Torr range, returning a high-pressure limit value of (4.7 ± 0.1) × 10^–13 cm³ molecule^–1 s^–1 at 293 K. A temperature dependence of k(CH₂OO + (CH₃)₂CO) = (1.4 ± 0.2) × 10^–21 T² exp(2421 ± 40/T) cm³ molecule^–1 s^–1 was observed in the 250–310 K range. The global chemical transport model (STOCHEM-CRI) was used to model the speciated Criegee intermediate field using the recently reported temperature-dependent rate coefficient values for various reactions of Criegee intermediates. The incorporation of the Criegee intermediate reaction with acetone in the model predicts decreases in acetone concentration of as much as 10–40 ppt in various regions of the world.