Self-consistent grain depletions and abundances I: The Orion Nebula as a
  test case
  Atomic species in the interstellar medium (ISM) transition out of their gas
phase mainly by depletion onto dust. In this study, we examine if there is any
change to the spectral line ratio predictions from a photoionization model of
the Orion H II region when the degree of dust depletions is altered according
to the most recently published model. We use equations and parameters published
by previous works, in order to streamline the calculation of depleted
abundances within CLOUDY. Our aim is for CLOUDY users to be able to vary the
level of depletion using a single parameter in the input file. This makes it
possible to explore predictions for a large range of depletions more
efficiently. Finally, we discuss the results obtained for a model of the Orion
Nebula when the degree of depletions are manipulated in this way. We found that
the intensity of line ratios are significantly affected by depletions onto dust
grains. Further, we found that adjusting dust abundances along with depletion
affects the structure and the overall temperature of the H$^+$ layer across the
H II region.
