Evidence of the impact of urban plumes on remote sites in the Eastern Mediterranean

Peroxyacetyl nitrate (PAN) is a well-known tracer of anthropogenically related impacts in photochemical smog formation and is usually found in heavily polluted urban air worldwide. Over the last decades its abundance in urban air has also been confirmed for Greek urban sites such as Athens or Thessaloniki. Due to the strong temperature dependence of PAN decomposition, PAN has also been identified as a long distance tracer of human activities. This behaviour is clearly discernible at low temperatures either under corresponding meteorological conditions or at higher altitudes. Information about the medium-range impact of PAN in the Eastern Mediterranean is still scarce. This study analyses PAN time series obtained simultaneously at two sites on the island of Crete located at two different altitudes (coastal site, mountain site at 1020 m a.s.l.; distance between the sites about 20 km) during the photochemical activity and solar ultraviolet radiation (PAUR-II) campaign in May/June 1999. Within the range of 270 km no metropolitan area is located, and the surrounding water surfaces represent an area almost free of stationary emission sources. The results from the PAUR-II campaign both show uniform diurnal variations of PAN at both sites indicating regional formation, as well as completely different patterns indicating that medium-range transport is effective. The metropolitan areas of Athens and Istanbul are likely emission sources.