From July 30th to August 1st 2012 three flights were carried out around Mt.Etna volcano as a part of the GMOS – European Tropospheric Mercury Experiment(ETMEP; www.gmos.eu).For this campaign the aircraft,a Rockwell Turbo Commander(www.blomasa.com)was equipped with three instruments for the measurement of Hg(2 x Tekran 2527,150 sec resolution; 1 x Lumex RA-915-AM,1 sec*),and instruments for measurements of CO(1 sec*),O3(1 sec*),SO2(1 sec*),and NO,NO2(1 sec*).Additional instruments were installed to obtain data for air temperature,pressure,relative humidity,and the 3-D aircraft position.The aircraft was equipped with custom made gas inlet to sample ambient air outside the aircraft boundary layer.The volcanic plume was identified by significantly increased SO2 concentration up to 800 ppb during all three flights(about 3 hours each).But only during the third flight the mercury concentration was elevated inside the plume by about 70%above the background(from 1.5 to 2.6 ng/m?).During the first two flights the mercury concentration inside the plume was comparable to those measured outside the plume(1.2 to 1.5 ng/m?).Concurrent to the ETMEP flights,ground based fully-speciated mercury as well as TGM,O3,and SO2 measurements were performed at 2700 m elevation at the Mt.Etnas north flank by the National Research Council of Italy(CNR-ⅡA; www.iia.cnr.it).During the third day a comparison was performed between airborne and ground-based measurements.In our presentation we will present the measured data for all three volcano flights and compare inside/outside volcanic plume measurements.We will also compare the airborne and the ground based measurements.