Impact of the new HNO3-forming channel of the HO2+NO reaction on tropospheric HNO3, NOx, HOx and ozone D. Cariolle1,2, M. J. Evans3, M. P. Chipperfield3, N. Butkovskaya4, A. Kukui5, and G. Le Bras4 1Centre Européen de Recherche et Formation Avancée en Calcul Scientifique, Toulouse, France 2Météo-France, Toulouse, France 3Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, UK 4Institut de Combustion, Aérothermique, Réactivité et Environnement, CNRS, Orléans, France 5Service d'Aéronomie, IPSL, CNRS, Paris, France
Abstract. We have studied the impact of the recently observed
on atmospheric chemistry. A pressure and temperature-dependent parameterisation
of this minor channel of the NO+HO2→NO2+OH reaction
has been included in both a 2-D stratosphere-troposphere model and a 3-D
tropospheric chemical transport model (CTM).
Significant effects on the nitrogen species and hydroxyl radical concentrations are found
throughout the troposphere, with the largest percentage changes occurring
in the tropical upper troposphere (UT).
Including the reaction leads to a reduction in NOx everywhere in the troposphere,
with the largest decrease of 25% in the tropical and Southern Hemisphere
UT. The tropical UT also has a corresponding large increase
in HNO3 of 25%. OH decreases throughout the troposphere with the largest reduction of over
20% in the tropical UT. The mean global decrease in OH is around 13%, which is very large compared
to the impact that typical photochemical revisions have on this modelled quantity.
This OH decrease leads to an increase
in CH4 lifetime of 5%. Due to the impact
of decreased NOx on the OH:HO2 partitioning, modelled HO2 actually increases
in the tropical UT on including the new reaction.
The impact on tropospheric ozone is a decrease in the range 5 to 12%, with
the largest impact in the tropics and Southern Hemisphere.
Comparison with observations shows that in the region of largest changes,
i.e. the tropical UT, the inclusion of the new reaction tends to degrade the model
agreement. Elsewhere the model comparisons are not able to critically assess the
impact of including this reaction.
Only small changes are calculated in the minor species distributions in the stratosphere.
Citation: Cariolle, D., Evans, M. J., Chipperfield, M. P., Butkovskaya, N., Kukui, A., and Le Bras, G.: Impact of the new HNO3-forming channel of the HO2+NO reaction on tropospheric HNO3, NOx, HOx and ozone, Atmos. Chem. Phys., 8, 4061-4068, doi:10.5194/acp-8-4061-2008, 2008.