Long-term (2002-2012) investigation of Saharan dust transport events at Mt. Cimone GAW global station, Italy (2165 m a.s.l.)

Mineral dust transport from North Africa towards the Mediterranean basin and Europe was monitored over an 11-y period (2002-2012) using the continuous observations made at Mt. Cimone WMO/GAW global station (CMN). CMN is in a strategic position for investigating the impact of mineral dust transported from northern Africa on the atmospheric composition of the Mediterranean basin and southern Europe. The identification of "dusty days" is based on coupling the measured in situ coarse aerosol particle number concentration with an analysis of modeled back trajectories tracing the origin of air masses from North Africa. More than 400 episodes of mineral dust transport were identified, accounting for 15.7% of the investigated period. Our analysis points to a clear seasonal cycle, with the highest frequency from spring to autumn, and a dust-induced variation of the coarse particle number concentration larger than 123% on a seasonal basis. In addition, FLEXTRA 10-d back trajectories showed that northwestern and central Africa are the major mineral dust source regions. Significant inter-annual variability of dust outbreak frequency and related mineral dust loading were detected and during spring the NAO index was positively correlated (R-2 = 0.32) with dust outbreak frequency. Lastly, the impact of transported mineral dust on the surface O-3 mixing ratio was quantified over the 11-y investigation period. Evidence of a non-linear and negative correlation between mineral dust and ozone concentrations was found, resulting in an average spring and summer decrease of the O-3 mixing ratio down to 7%.