Six-day PM10 air quality forecasts for The Netherlands with the chemistry transport model Lotos-Euros

In this work we study the ability of the chemistry transport model Lotos-Euros to forecast, with a range of six days, PM10 concentrations and exceedances thereof. The model performance remains good up to a lead time of three days. After that the results gradually deteriorate because the PM10 forecast is increasingly affected by uncertainty in the meteorological forecast. For a lead time of 6 days, however, the forecast still has skill and still complies with general performance criteria. The correlation between forecast and observations is about 0.69 for the first half of the forecast and remains above 0.53 until the end of the forecast range. Exceedances of the PM10 concentration over a threshold are forecasted with good skill up to a forecast range of three days, after which a gradual deterioration sets in. Furthermore, the stability of the forecast displays the same behaviour. Up to a lead time of three days, the forecast remains reasonably stable with more than 80% of forecasted exceedances still present in all later shorter-term forecasts for the same date. Because exceedances can be forecasted with considerable skill a number of days in advance, the forecast can be used for applications that require a range of a few days, such as the scheduling and implementation of short-term emission reduction measures.