a significant effect on the structure of the system.

One example of a photoionized gas where the gravitational acceleration is not negligible is the Galactic interstellar medium (ISM). Although interstellar matter only accounts for a relatively small fraction of the total disk mass, it plays a crucial role on the formation and evolution of the Galaxy. New stars are formed from the cold molecular phase of the ISM, and the energy input from the stellar population [[influences]{}]{} the structure and composition of the interstellar gas. The complex interplay between gas, stars, cosmic rays, and magnetic fields is responsible for the rich structure, dynamics, and observational phenomenology of our Galaxy [see e.g. @Ferriere01].

The present work describes the implementation of gravitational hydrostatic equilibrium in the plasma physics code [Cloudy]{}, last described by @Ferland+98. Numerical details are given in Section \[secCloudy\] and Appendix \[secUserGuide\]. Section \[secResults\] discusses the results obtained for the vertical structure of the Milky Way disk in the solar neighbourhood, and a brief summary is given in Section \[secConclusions\].

Numerical implementation {#secCloudy}
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The [Cloudy]{} photoionization code computes the ionization structure, level populations, electron temperature, and observable spectrum of a gas, given its chemical composition and the spectrum of 