Abstract
Abstract. A detailed 3-D evaluation of an ensemble of five regional Chemistry Transport Models (RCTM) and one global CTM with focus on free tropospheric ozone over Europe is presented. It is performed over a summer period (June to August 2008) in the context of the GEMS-RAQ project. A data set of about 400 vertical ozone profiles from balloon soundings and commercial aircraft at 11 different locations is used for model evaluation, in addition to satellite measurements with the infrared nadir sounder (IASI) showing largest sensitivity to free tropospheric ozone. In the middle troposphere, the four regional models using the same top and boundary conditions from IFS-MOZART exhibit a systematic negative bias with respect to observed profiles of about −20%. Root Mean Square Error (RMSE) values are constantly growing with altitude, from 22% to 32% to 53%, respectively for 0–2 km, 2–8 km and 8–10 km height ranges. Lowest correlation is found in the middle troposphere, with minimum coefficients (R) between 0.2 to 0.45 near 8 km, as compared to 0.7 near the surface and similar values around 10 km. A sensitivity test made with the CHIMERE mode also shows that using hourly instead of monthly chemical boundary conditions generally improves the model skill (i.e. improve RMSE and correlation). Lower tropospheric 0–6 km partial ozone columns derived from IASI show a clear North-South gradient over Europe, which is qualitatively reproduced by the models. Also the temporal variability showing decreasing ozone concentrations in the lower troposphere (0–6 km columns) during summer is well reproduced by models even if systematic bias remains (the value of the bias being also controlled by the type of used boundary conditions). A multi-day case study of a trough with low tropopause was conducted and showed that both IASI and models were able to resolve strong horizontal gradients of middle and upper tropospheric ozone occurring in the vicinity of an upper tropospheric frontal zone.
Highlights
Regional Chemical Transport Models (RCTM) are central tools of air quality policy
In the Planetary Boundary Layer (PBL), mean ozone concentration is about 46 ppb with a 12.4 ppb standard deviation (Table 3)
Root Mean Square Error (RMSE) is almost constant in the PBL with a median value of about 10 ppb (22 %) (Fig. 3; Table 3)
Summary
Regional Chemical Transport Models (RCTM) are central tools of air quality policy. A specific exercise has been set-up where five of the GEMS-RAQ RCTM have re-simulated the summer 2008 period, with, for some of them, new configurations allowing simulating the whole troposphere These models are state-of-the-art models in Europe and together they are a representative sample of European RCTM’s. They will be compared against an extended set of tropospheric ozone measurements from sondes, commercial aircraft (MOZAIC), and thermal-infrared measurements onboard satellite (IASI). To our knowledge, this is the first study that uses IASI ozone observations to evaluate RCTM’s. 52.1◦ N, 5.18◦ E 52.4◦ N, 20.97◦ E 46.8◦ N, 6.95◦ E 50.8◦ N, 4.35◦ E 47.8◦ N, 11◦ E 60.14◦ N, 1.19◦ W 67.37◦ N, 26.63◦ E 51.93◦ N, 10.25◦ W 40.47◦ N, 3.58◦ W
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