A sensitivity study of the operational surface ozone forecast system "DACFOS"

The Danish Atmospheric Chemistry FOrecasting System (DACFOS) is a receptor point model based on DMI's transport model using data from the numerical we ather prediction model DMI-HIRLAM and employing EMEP's chemistry scheme fro m the MSC-W oxidant model. Surface ozone forecasts tot the summers 1997-98 al AREARE verified for two English and two Danish stations, using the stati stical parameters suggested by the Technical Working Group on Ozone Forecas ting and Data Exchange (TWG-DFO). The forecast skill varies for the two cou ntries, and a relative high positive, bias is seen for the English forecast s in comparison with the Danish forecasts. This high positive bias is inves tigated by a sensitivity study considering cases with different air masses classified by the German Weather Service (DWD). The study shows that the po sitive bias for England originated from polar and midlatitudinal continenta l airmasses. These air masses do travel over different emission areas when they arrive to, Denmark and England, so the difference in bias could he exp lained by inaccurate emissions. (C) 2000 Elsevier Science Ltd. All rights r eserved.