The atmospheres of the planetary bodies in our solar system have diverse chemistry and radiation environments. Recent studies of Titan’s ionosphere using Cassini observations have revealed the presence of heavy positive and negative ions. Similarly, negatively charged water group cluster ions have been found in the plume of Saturn’s moon Enceladus. The Rosetta mission to comet 67P/Churyumov-Gerasimenko, which uniquely follows the comet towards the sun, is expected to teach us more about the chemistry and the relevant chemical processes occurring in the coma. Beyond our solar system, the extensive planetary surveys from Kepler and CoRoT have detected the presence of numerous exoplanets orbiting different spectral-type stars. UV transit observations of the thermospheres for some of these exoplanets reveal a chemical composition that has both similarities to the planets of our solar system, but also striking differences. This session focuses on the comparison of chemical processes in atmospheres and ionospheres of solar system planets, exoplanets and moons as well as in cometary comae. Contributions on all aspects of gas phase chemistry, from simple molecules and ions to the formation, evolution and composition of aerosols are welcome. We would like to bring together experts in observations, modelling, laboratory experiments and relevant instrumentation for ongoing/future missions.