Winter Southern wind flow and air pollution episodes over Athens, Greece

The greater area comprising the Attica peninsula and the Saronic Gulf is greatly influenced by various local circulation types. During winter months, moderately high air pollutants concentrations are observed when the prevailing condition is either stagnant or a weak southern flow. The case studied in this paper regards an episode that occurred in mid-December. This episode is characterized by very weak pressure gradient over Greece, and very little change in wind speed and direction with height, without the precedence of exceptionally strong warm advection in the lower troposphere during the days before the episode. This episode was not characterized by very high air pollution values, a rather common feature during December, that even though it presents one of the highest episode frequencies, the observed values are not high enough to require the enforcement of restrictive measures.