Comparison of OMI NO2 tropospheric columns with an ensemble of global and European regional air quality models V. Huijnen1, H. J. Eskes1, A. Poupkou2, H. Elbern3, K. F. Boersma1, G. Foret4, M. Sofiev5, A. Valdebenito6, J. Flemming7, O. Stein8,9, A. Gross10, L. Robertson11, M. D'Isidoro12, I. Kioutsioukis2, E. Friese3, B. Amstrup10, R. Bergstrom11, A. Strunk3, J. Vira5, D. Zyryanov4,14, A. Maurizi12, D. Melas2, V.-H. Peuch13, and C. Zerefos2 1Royal Netherlands Meteorological Institute, De Bilt, The Netherlands 2Laboratory of Climatology, Faculty of Geology, University of Athens, Athens, Greece 3Rhenish Institute for Environmental Research at the University of Cologne, Köln, Germany 4Laboratoire Interuniv. des Systèmes Atmosphériques, CNRS/Univ. Paris 12 et 7, Créteil, France 5Air Quality Research, Finnish Meteorological Institute, Finland 6Norwegian Meteorological Institute, Norway 7European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, UK 8Institute for Chemistry and Dynamics of the Geosphere (ICG), FZ Jülich, Germany 9Max Planck Institute for Meteorology, Hamburg, Germany 10Danish Meteorological Institute, Copenhagen, Denmark 11Swedish Meteorological and Hydrological Institute, Norrkoping, Sweden 12Institute of Atmospheric Sciences and Climate, Consiglio Nazionale delle Ricerche, Bologna, Italy 13CNRM-GAME, Météo-France and CNRS URA 1357, Toulouse, France 14Laboratoire de Météorologie Dynamique, CNRS/IPSL, Ecole polytechnique, Palaiseau, France
Abstract. We present a comparison of tropospheric NO2 from OMI measurements to the
median of an ensemble of Regional Air Quality (RAQ) models, and an
intercomparison of the contributing RAQ models and two global models for the
period July 2008–June 2009 over Europe. The model forecasts were produced
routinely on a daily basis in the context of the European GEMS ("Global and
regional Earth-system (atmosphere) Monitoring using Satellite and in-situ
data") project. The tropospheric vertical column of the RAQ ensemble median
shows a spatial distribution which agrees well with the OMI NO2
observations, with a correlation r=0.8. This is higher than the
correlations from any one of the individual RAQ models, which supports the
use of a model ensemble approach for regional air pollution forecasting. The
global models show high correlations compared to OMI, but with
significantly less spatial detail, due to their coarser resolution.
Deviations in the tropospheric NO2 columns of individual RAQ models from
the mean were in the range of 20–34% in winter and 40–62% in summer,
suggesting that the RAQ ensemble prediction is relatively more uncertain in
the summer months.
The ensemble median shows a stronger seasonal cycle of NO2 columns than OMI, and the
ensemble is on average 50% below the OMI observations in summer, whereas in winter the bias is small.
On the other hand the ensemble median shows a somewhat weaker seasonal cycle than NO2
surface observations from the Dutch Air Quality Network, and on average a negative bias of 14%.
Full profile information was available for two RAQ models and for the global models. For these models the retrieval averaging kernel was applied.
Minor differences are found for area-averaged model columns with and without applying the kernel,
which shows that the impact of replacing the a priori profiles by the RAQ model profiles is on average small.
However, the contrast between major hotspots and rural areas is stronger for the direct modeled vertical columns
than the columns where the averaging kernels are applied, related to a larger relative contribution of the free troposphere and
the coarse horizontal resolution in the a priori profiles compared to the RAQ models.
In line with validation results reported in the literature, summertime concentrations
in the lowermost boundary layer in the a priori profiles from the DOMINO product
are significantly larger than the RAQ model concentrations and
surface observations over the Netherlands. This affects the profile shape, and contributes to
a high bias in OMI tropospheric columns over polluted regions.
The global models indicate that the upper troposphere may contribute significantly to
the total column and it is important to account for this in comparisons with RAQ models.
A combination of upper troposphere model biases,
the a priori profile effects and DOMINO product retrieval issues
could explain the discrepancy observed between the OMI observations and the ensemble median in summer.
Citation: Huijnen, V., Eskes, H. J., Poupkou, A., Elbern, H., Boersma, K. F., Foret, G., Sofiev, M., Valdebenito, A., Flemming, J., Stein, O., Gross, A., Robertson, L., D'Isidoro, M., Kioutsioukis, I., Friese, E., Amstrup, B., Bergstrom, R., Strunk, A., Vira, J., Zyryanov, D., Maurizi, A., Melas, D., Peuch, V.-H., and Zerefos, C.: Comparison of OMI NO2 tropospheric columns with an ensemble of global and European regional air quality models, Atmos. Chem. Phys., 10, 3273-3296, doi:10.5194/acp-10-3273-2010, 2010.