Stability curves of pure condensates (horizontal lines) and cooling curves of the protoplanetary disc model (vertical lines) at two given distances to the star: 5 and 20 AU (the evolution of the disc proceeds from high to low temperatures), for irradiated (grey lines) and non-irradiated (black lines) discs. Species remain in the gas phase above the stability curves. Below, they condense as pure ices. Model with CO:CO₂ = 1:1.