Impact of HARMONIE high-resolution meteorological forecasts on the air quality simulations of LOTOS-EUROS

In this study, we couple the LOTOS-EUROS model with high resolution meteorological forecasts from the Harmonie model to study the impact on air quality in comparison to simulations driven by ECMWF meteorological forecasts. The main purpose of this study is to compare the differences in meteorological variables between the ECMWF and Harmonie model, and analyse the impact of these differences on the air quality simulations of LOTOS-EUROS. A comparison of the meteorological variables shows that the capability of these two models to simulate the surface temperature, relative humidity and wind speed is similar. Because of the high resolution of Harmonie, there are clear differences in meteorological variables between ECMWF and Harmonie, especially at the coast, over forest and urban areas. We performed a comparison of model meteorological forecasts with observations in the Netherlands. Apart from the boundary layer height (BLH), it is hard to conclude which meteorological model gives better scores. The boundary layer height simulated by Harmonie is significantly lower than for the ECMWF model. Also independent ceilometer observations show that the Harmonie BLH is too low during clear days in Summer 2012. The differences in the meteorological fields lead to significant changes in the local air pollutant concentrations. The root mean square difference (RMSD) between two simulations is 4ug/m3 for PM10; 20ug/m3 for O3; 6ug/m3 for NO2; 5ug/m3 for NO. However, the daily mean difference of PM10 concentration is small and the mean differences of other air pollutant concentration are not significant. We performed a sensitivity analysis of air quality on surface temperature, relative humidity, surface wind speed and boundary layer height. The effect of a 2K difference of surface temperature is very small. With a 10% increase of relative humidity at all layers, the concentration of PM10 increases and the concentration of secondary inorganic aerosols (SIA) gas precursors decreases. The impact on ozone is not significant. An increase of surface wind speed makes the PM10 concentration decrease over the land and increase over sea and near the coastline. The PM10 concentration decreases when the boundary layer height is increased. In contrast, the O3 concentration sometimes increases when the boundary layer height is increased, especially at night.