Evaluation of the CMAQ5.0 in the framework of the CALIOPE air quality forecasting system over Europe

Abstract

CALIOPE is a high-resolution air quality system which provides forecast for 24 and 48h since October 2006 for Europe (12 km x 12 km, 1h) and Spain (4 km x 4 km, 1h). The meteorological model is the WRF-ARW model (version 3.2.1) initialized by the FNL/NCEP data. The emissions are estimated by means a top-down approach implemented in the High-Elective Resolution Modeling Emission System (HERMES version 2.0) based on the EMEP inventory for the year 2008. The Chemical Transport Model (CTM) is the CMAQ (version 4.5) using the CB-IV chemical mechanism and AERO4 mode for aerosols. Several evaluation studies and near-real time evaluation (NRT) against air quality measurements on an hourly basis support the confidence on the system. The present contribution evaluates the CALIOPE system over Europe using CMAQ CTM version 5.0 (CB05 and AERO5) which is working in forecast mode since 9 April 2012. The comparison between both CMAQ versions is done in terms of gaseous and aerosol concentrations (O3, NO2, SO2, PM10, and PM2.5) at the lowest level. Forecast concentrations are compared against observations on an hourly basis from the European air quality database (Airbase) which classifies stations as background rural/suburban. Results indicate that CMAQv5.0 improves O3 forecast daily cycle, especially at nighttime over suburban stations, where O3 biases are reduced between 20 and 40 µgm-3. The CMAQv5.0 improves the forecast of NO2 peaks at suburban stations reducing biases ~10-20 µgm-3. PM10 forecast also improves with the new CMAQ version. Episodes of secondary aerosol formation are now reproduced (i.e. 7-14 may 2012), where bias are reduce in ~10-20 µgm-3. Furthermore, PM10 hourly peaks in suburban stations are better reproduced reducing hourly biases ~5-10 µgm-3. The contribution also evaluates the effect of using the Kalman filter post-process to reduce systematic bias in both CMAQ versions. Results show that the bias-adjustment technique is more effective over CMAQv5.0.