Height and seasonal dependence of aerosol optical properties over southeast Italy

Systematic Raman lidar measurements performed from May 2000 to August 2002 in the framework of the European Aerosol Research Lidar Network are analyzed and discussed. Main results on height dependence and seasonal cycle of extinction alpha(z) and backscatter beta(z) coefficients, aerosol optical depths AOD(z), and lidar ratios S(z) are presented. Yearly-averaged vertical profiles of extinction and backscatter coefficients reveal that both alpha(z) and beta(z) decrease more than 75% within the lowermost 2 km. Yearly-averaged lidar ratios increase from about 42-48 sr in the lowermost 2 km to between 67-72 sr in the air masses above 2 km. The changes in lidar ratios are indicative of changes in the physical characteristics of the monitored aerosols and suggest that over the monitoring site, the lowermost air masses (z < 2 km) are on average characterized by a larger concentration of particles leading to S values typical of marine aerosols, while the elevated air masses (z > 2 km) are characterized by lidar ratios typical of continental aerosol type. The seasonal cycle analysis reveals that the average maximum height z(M) at which aerosols are detected by the lidar that is about 5 km in spring-summer, and decreases up to about 3 km in autumn-winter. Monthly AODs span the 0.16-0.26 range in autumn-winter and the 0.26-0.4 range in spring-summer. The scarce renovation of air masses, occurring in spring-summer as a consequence of the weather stability, favours the accumulation of the atmospheric aerosol particles and may account for the larger AODs and z(M) values.