On the meteorological conditions during some strong smoke episodes in Athens

Data of smoke concentrations from two stations in the downtown Athens area, were used to select eight intense air pollution episodes lasting a total of 31 days in the cold months of the period 1984–1987. The onset of these episodes was found to have been associated with a warm air advection from the south-west or with the withdrawal of a cold air mass that had been previously established over Greece. Rawinsonde data indicated that an intense warming below the 850 mb layer also occured during the first day in seven of the eight episodes, denoting the existence of strong subsidence. During 90% of the episode days the maximum 3-hourly resultant wind speed was less than 2.0 m s⁻¹ between 0000 and 1200 LST, while the mean mixing height was less than 500 m in 65% of the days; only on 1 did it exceed 1000 m. Finally, the end of the episodes was found to have been caused in four of the cases by a cooling of the lowest layers of the troposphere produced by the passage of a weak cold front and in three cases by a substantial increase in the wind or the wixing height.