Abstract
Abstract. Here, the capability of the chemical weather forecasting model CHIMERE (version 2017r4) to reproduce surface ozone, particulate matter and nitrogen dioxide concentrations in complex terrain is investigated for the period from 21 June to 21 August 2018. 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. Driven by lateral boundary conditions from the European Centre for Medium-Range Weather Forecasts (ECMWF) Composition Integrated Forecast System, anthropogenic emissions from two commonly used top-down inventories and meteorological data from the Weather Research and Forecasting Model, CHIMERE's performance with respect to observations is tested with a range of sensitivity experiments. We assess the effects of (1) an increase in horizontal resolution, (2) an increase in vertical resolution, (3) the use of distinct model chemistries, and (4) the use of distinct anthropogenic emissions inventories, downscaling techniques and land use databases. In comparison with the older HTAP emission inventory downscaled with basic options, the updated and sophistically downscaled EMEP inventory only leads to partial model improvements, and so does the computationally costly horizontal resolution increase. Model performance changes caused by the choice of distinct chemical mechanisms are not systematic either and rather depend on the considered anthropogenic emission configuration and pollutant. Although the results are thus heterogeneous in general terms, the model's response to a vertical resolution increase confined to the lower to middle troposphere is homogeneous in the sense of improving virtually all verification aspects. For our study region and the two aforementioned top-down emission inventories, we conclude that it is not necessary to run CHIMERE on a horizontal mesh much finer than the native grid of these inventories. A relatively coarse horizontal mesh combined with 20 model layers between 999 and 500 hPa is sufficient to yield balanced results. The chemical mechanism should be chosen as a function of the intended application.
Highlights
Motivated by the air quality legislation of the European Union (EU, 2008), many governmental air quality departments are currently demanding air quality forecasting schemes based on numerical models (Thunis et al, 2016), and the need for accurate and computationally efficient predictions in this field is perhaps greater than ever before
Brands et al.: CHIMERE’s performance over the NW Iberian Peninsula comprising an ensemble of seven chemical weather forecasting (CWF) models1 run for the entire continent at a horizontal resolution of 0.1 to 0.25◦ in longitude and 0.1 to 0.2◦ in latitude. In addition to this short-term prediction system, several large research initiatives have been issued during the last 2 decades in order to assess the climatological properties of atmospheric composition, including the detection of long-term trends resulting from emission reductions induced by the Convention on Long-range Transboundary Air Pollution (CLRTAP, 2019)
The meteorological input data for the CHIMERE experiments are provided by the Weather Research and Forecasting (WRF) model version 3.5 (Skamarock et al, 2008), driven by Global Forecast System (GFS) forecasts initialized at 00:00 UTC (Caplan et al, 1997)
Summary
Motivated by the air quality legislation of the European Union (EU, 2008), many governmental air quality departments are currently demanding air quality forecasting schemes based on numerical models (Thunis et al, 2016), and the need for accurate and computationally efficient predictions in this field is perhaps greater than ever before. Brands et al.: CHIMERE’s performance over the NW Iberian Peninsula comprising an ensemble of seven chemical weather forecasting (CWF) models run for the entire continent at a horizontal resolution of 0.1 to 0.25◦ in longitude and 0.1 to 0.2◦ in latitude In addition to this short-term prediction system, several large research initiatives have been issued during the last 2 decades in order to assess the climatological properties of atmospheric composition, including the detection of long-term trends resulting from emission reductions induced by the Convention on Long-range Transboundary Air Pollution (CLRTAP, 2019). A common limitation of small-scale sensitivity studies is that their conclusions, strictly speaking, only hold for the considered region, time period or season of the year In this context, most of the aforementioned conclusions for CHIMERE (the model applied here) have been drawn for the Île de France region, which is densely populated, relatively flat and not directly influenced by sea-salt emissions.
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