  Empirical constraints of fundamental properties of protoplanetary disks are
essential for understanding planet formation and planetary properties (1,2).
Carbon monoxide (CO) gas is often used to constrain disk properties (3).
However, estimates show that the CO gas abundance in disks is depleted relative
to expected values (4,5,6,7), and models of various disk processes impacting
the CO abundance could not explain this depletion on observed 1Myr timescales
(8,9,10,11,12,13,14). Here we demonstrate that surface energy effects on
particles in disks, such as the Kelvin effect, that arise when ice
heterogeneously nucleates onto an existing particle can efficiently trap CO in
its ice phase. In previous ice formation models, CO gas was released when small
ice-coated particles were lofted to warmed disk layers. Our model can reproduce
the observed abundance, distribution and time evolution of gaseous CO in the
four most studied protoplanetary disks (7). We constrain the solid and gaseous
CO inventory at the midplane and disk diffusivities and resolve inconsistencies
in estimates of the disk mass -- three crucial parameters that control
planetary formation.
