Comparison of OMI NO<sub>2</sub> tropospheric columns with an ensemble of global and European regional air quality models

Abstract

Abstract. We present a comparison of tropospheric NO 2 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 NO 2 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 Correspondence to: V. Huijnen (huijnen@knmi.nl) to OMI, but with significantly less spatial detail, due to their coarser resolution. Deviations in the tropospheric NO 2 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 NO 2 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 NO 2 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.Published by Copernicus Publications on behalf of the European Geosciences Union. V. Huijnen et al.:Comparison of NO 2 in regional and global models to OMI 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 effec...

High-resolution airborne imaging DOAS measurements of NO<sub>2</sub> above Bucharest during AROMAT

“…(2) and (3) to the one used by Popp et al (2012). A tropospheric vertical column of VCD trop 0 = 1 × 10 15 molec cm −2 is assumed over the background region, which is a representative value for Europe during the summer period as shown in Huijnen et al (2010). The background spectrum is an averaged spectrum from 120 individual spectra, which may have different AMFs caused by changing conditions (geometry, surface reflectance) between these measurements.…”

Online coupled regional meteorology chemistry models in Europe: current status and prospects

“…Equations for atmospheric dynamics, thermodynamics, radiation, microphysics and chemistry are solved simultaneously on the same spatio-temporal grid making every feedback potentially available. BOLCHEM was run in forecast mode over Europe during the GEMS project (http://gems.ecmwf.int/; Huijnen et al, 2010;Zyryanov et al, 2012) and is currently running to forecast Air Quality over Italy in the MACC project (http: //www.gmes-atmosphere.eu/). It also participated within the CityZen project (http://www.cityzen-project.eu) to regional trend and future scenario studies (Colette et al, 2011).…”

Regional scale ozone data assimilation using an ensemble Kalman filter and the CHIMERE chemical transport model

“…For instance, model simulations have been compared against ozone surface observations in Europe (Vautard et al, 2007 and in the United States (Solazzo et al, 2012b) in the context of the AQMEII (Air Quality Model Evaluation International Initiative). Ensembles of model simulations and their statistical combinations have also been evaluated against satellite observations for tropospheric NO 2 (Huijnen et al, 2010) and O 3 (Zyryanov et al, 2012). These studies helped to identify if uncertainties given by the ensemble spread can represent the error distribution for instance in terms of geographical and temporal patterns.…”