Theoretical t-HCOOH relative abundance to molecular hydrogen. Panel (a): spatial distribution of the gas-phase abundance as a function of the radial distance from the central star and the altitude over the midplane. The white contours denote log10(﹩{n}_{{{\rm{H}}}_{2}}﹩) in cm−3. Panel (b): the same as in A but for the HCOOH ice. Panel (c): radial distribution of column densities of gas (blue line) and solid (dashed orange line) HCOOH. The gray line shows the measured HCOOH column density. The predictions are based on our physical and chemical model (Parfenov et al. 2017, see Section 4).