Evaluation of Snowpack O3 and NOx Exchange at Summit, Greenland in a Single-Column Chemistry-climate Model

The objective of this study is to develop and evaluate a process-based representation of snowpack O₃ and NO_x exchange at Summit, Greenland for implementation in global chemistry–climate models. This development and evaluation activity uses a single-column model (SCM) version of the chemistry–climate model ECHAM4 coupled with ECMWF reanalysis. It contains explicit representation of atmosphere–biosphere surface trace gas exchange using a multi-layer canopy exchange model, which serves as the basis for implementing a mechanistic representation of snowpack gas exchanges. The new parametrization of snowpack processes is developed from observations presented at this meeting by Van Dam et al. and Toro et al.

First, micrometeorological observations (e.g. solar radiation, wind speed, air and snowpack temperatures, and pressure) of the SCM were evaluated. Second, the accuracy of simulated snow–atmosphere ozone fluxes was assessed. The SCM appropriately simulates the micrometeorology prerequisite to a fair evaluation of exchange of chemical compounds. The SCM also is able to suitably simulate ozone concentration gradients and fluxes between the snowpack and the snow surface when a first-order in-snowpack removal rate is imposed. Further development will be require to explicitly explain this removal rate as a function of physical and chemical sink processes in the snowpack.

Eventually, the updated SCM will be transformed into a new snowpack module to be used in the global chemistry climate model EMAC (ECHAM5-MESSy Atmospheric Chemistry model) to simulate the impact of air–snow O₃ and NO_x exchange upon the Arctic tropospheric O₃ budget.