density decreases. Gas temperature and pressure as a function of $z$ are shown in Figure \[figP\]. The temperature of the cold dense phase is of the order of $10-100$ K, while the diffuse gas ranges from $5000$ to $10000$ K. Gas pressure is roughly constant up to the ionization front, but it decreases rapidly through the molecular layer due to the high gas densities (above $100$ cm$^{-3}$). The pressure stabilizes again in the outer region, although the gravitational acceleration imposes a negative pressure (and density) gradient. The effect increases with distance; at some point, the cumulative gas mass and therefore the gravitational force are so high that both density and pressure decay extremely fast. Gas temperature, on the other hand, increases steadily towards the Galactic halo.

This structure does not provide a realistic description of the local ISM. On the one hand, the approximation that all the radiation comes from an infinitely thin disk at the mid plane creates a photoionized region at low $z$. Although there is indeed a thin layer of ionized gas near the Galactic plane, composed of both discrete [Hii]{} regions and diffuse gas [see e.g. @Paladini+05], its contribution near the solar neighbourhood is negligible [e.g. 