Gas-phase CO in protoplanetary disks: A challenge for turbulent mixing

This is the first paper in a series in which we study the influence of turbulent diffusion and advective transport on the chemical evolution of protoplanetary disks, using a 2D flared-disk model and a 2D-mixing gas-grain chemical code with surface reactions. A first interesting result concerns the abundance of gas-phase CO in the outer regions of protoplanetary disks. In this Letter we argue that the gas-phase CO concentration in the disk regions, where the temperature is lower than similar to 25 K, can be significantly enhanced due to the combined effect of vertical and radial mixing. This finding has a potential implication for the current observational data on the DM Tau disk chemistry.