Atmospheric Chemistry

In this article it is described how to perform different kinds of atmospheric chemistry simulations. This includes the description of simulations with a simplified chemistry and MECCA-based (full) chemistry, their nameless settings, possible modules to make use of and information about initialization data. Further, there are given some examples of typical simulation you can do with ICON-ART including atmospheric chemistry.

Simplified Chemistry

When we talk about simplified calculated chemistry in ICON-ART, we mean that the concentration of the gases we want to simulate is calculated with a parametrization. Here production and depletion rates are calculated to solve the differential equation

${\frac {\mathrm {dc_{i}} }{/}}{\mathrm {dt} }=P_{i}-{\frac {c_{i}}{/}}{\tau _{i}}$

numerically. Here, $c_{i}$ describes the number concentration of a certain tracer, $c_{i}$ describes the chemical production and $\tau _{i}$is the belonging life time of tracer $i$. For the namelist settings you are able to use for atmospheric chemistry, check out the ART-namelist parameters (see ART namelists). To learn more about technical details of simplified chemistry, see also Weimer et. al. (2017)

Note: When enabling simplified chemistry with the switch lart_chemtracer = .TRUE., you can improve your runtime but the simulated concentration values are less exact compared to MECCA-based chemistry.

MECCA-based Chemistry

The MECCA(=Module Efficiently Calculating the Chemistry of the Atmosphere) based chemistry describes a full gas phase chemistry that can be applied as an extension to the parametrized Simplified Chemistry. MECCA itself is originally a submodule of the CAABA box model where an air parcel is described as a box and outgoing from this model all exchange processes in- and outward of the box are calculated. As MECCA is part of this model, it contains a wide collection of the most important reactions, including Ozone-, Methane-, HOx-, NOx-, Carbonhydrogen-, Halogene- and Sulfur chemistry. MECCA is available in a supplement, available to download for free and containing all auxiliaries to perform MECCA-simulations. The collection of the gase phase chemistry reactions can be found in the supplement in the gas.eqn (path: caaba3.0/Mecca/gas.eqn). Additionally it is also possible to edit existing reactions as well as creating new reactions with the help of "Replacement-files" (see an example in the Configurations part). Inside the gas.eqn every reaction is marked with a certain code. To select your specific reactions for the machanism you can set labels to your belonging reactions or, more easily, you can create a new Gas-Equation-file gas_Mechanism1.eqn, containing only the wanted reactions. (Note: Never edit the original gas.eqn! Better copy it in the first place and then rename and edit it, depending on your desires.)

Configurations

Soon some examples for Atmospheric Chemistry simulations will be shown here.

-Work in progress-