Sensitivity of CHIMERE to changes in model resolution and chemistry over the northwestern Iberian Peninsula

Abstract. Here, the capability of the chemical weather forecasting model CHIMERE (version 2017r4) to reproduce summertime surface ozone, particulate matter and nitrogen dioxide concentrations in complex terrain is investigated. The study area is the northwestern Iberian Peninsula, where both coastal and mountain climates can be found in direct vicinity and a large fraction of the land area is covered by forests. Fed by lateral boundary conditions from the ECMWF Composition Integrated Forecast System, meteorological data from the Weather Research and Forecasting Model (WRF) and the HTAP v2.2 emission inventory, CHIMERE's performance compared to observations is tested with a range of sensitivity experiments, exploring the role of horizontal and vertical resolution and the effects of applying distinct chemistry mechanisms. Using a high horizontal and vertical resolution yields the most balanced verification results. If both the daily maximum and minimum values are important for the given application, then the full Melchior mechanism should be used. If, however, the daily maxima are considered more important than the minima, SAPRC should be used instead. In any case, model performance for nitrogen dioxide is clearly not satisfactory for our study region, probably indicating deficiencies in the emission inventory.