Cyclones are a key element of the atmospheric circulation in the midlatitudes (Carlson, 1998). Cyclogenesis, for which a first conceptual model was presented by the Bergen school (Bjerknes, 1910), occurs most frequently at the polar front. The various ascending and descending airstreams typically associated with these cyclones carry a range of different chemical signatures (Cooper et al., 2002). The so-called warm conveyor belt (WCB) – a strongly ascending airstream ahead of a cyclone’s cold front (Browning et al., 1973) – is an important mechanism to lift air pollutants emitted at the sur- face into the upper troposphere, where the faster winds facil- itate their intercontinental transport (ICT) (Stohl and Trickl, 1999). Thus,.
