Technical note:: The new comprehensive atmospheric chemistry module MECCA

In this technical note we present the multi-purpose atmospheric chemistry model MECCA. Owing to its versatility and modular structure, it can be used for tropospheric as well as stratospheric chemistry calculations. Extending the code to other domains (e.g. mesospheric or oceanic chemistry) is easily possible. MECCA contains a comprehensive atmospheric reaction mechanism that currently includes: 1) the basic O-3, CH4, HOx, and NOx chemistry, 2) non-methane hydrocarbon (NMHC) chemistry, 3) halogen (Cl, Br, I) chemistry, and 4) sulfur chemistry. Not only gas-phase chemistry but also aqueous-phase and heterogeneous reactions are considered. Arbitrary subsets of the comprehensive mechanism can be selected according to the research objectives. The program code resulting from the chemical mechanism can easily be used in any model, from a simple box model to a comprehensive global general circulation model. As part of the model development, one often needs to combine several chemistry mechanisms. Another frequently occuring task is coupling chemical mechanisms to a meteorological model, for example, for an intercomparison. Unfortunately, these are both time-consuming tasks due to different approaches and incompatibilities between the codes. Also, it is often complicated because there is no clear separation between the meteorological and the chemical part of the model, and such a setup is sensitive to errors. In our implementation we apply a new approach aimed at avoiding the above mentioned problems. Here, we present the new comprehensive and flexible atmospheric chemistry module MECCA (Module Efficiently Calculating the Chemistry of the Atmosphere).