Reactions and rate constants form the basis of atmospheric chemistry. Chemistry transport models use these rate constants to calculate atmospheric composition, with these calculations go on to form the basis of air quality and climate policy. There are however known uncertainties associated with these rate constants which are often ignored. Here we explore the impact of rate constant uncertainties in the GEOS-Chem model of tropospheric chemistry and transport. We show that the model has a significant degree of linearity with respect to rate constant perturbations and thus we can perturb the rate constants individually and evaluate the overall uncertainty by adding these individual perturbations together in quadrature. We evaluate the impact of the rate constant uncertainty for all of the inorganic reactions and for some of the organic reactions in the model. We use a range of metrics of atmospheric performance for the present day (ozone burden, surface ozone, global mean OH, max surface ozone etc). Largest uncertainties are found at the coldest temperatures such the upper troposphere. Overall uncertainties for O3 burden and mean OH concentration are of the order of 15%. Uncertainties in surface ozone are smaller due to the higher temperatures. Basic inorganic reactions with significant fluxes (O3+NO, NO+HO2, O(1D)+N2 etc) are the source of much of the rate constant uncertainty in the model. The top ten reactions causing uncertainty in the model will be presented.

Uncertainties in global atmospheric composition due to uncertainties in inorganic and organic rate constants

249th National Meeting (2015)

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