Within the Global Mercury Observation System project(GMOS,www.gmos.eu)vertical profiles were flown downwind of a modern coal fired power plant in central Europe on August 21th and 22nd,2013.Along both flights the gaseous elemental mercury concentration(GEM)was measured with a Tekran 2537X analyser(resolution: 150 s)and a Lumex RA-915-AM(raw signal resolution: 1 s).Furthermore a second Tekran was operated as backup instrument,measuring the total gaseous mercury concentration(resolution: 150 s).During the profiling on August 21th,additionally gaseous oxidized mercury(GOM)was sampled onto a denuder and was analysed after the flight in laboratory.In addition to the mercury measurements,the research aircraft,a CASA-212 with a custom-built air inlet,measured SO2,CO,O3,NO,NO2,as well as basic meteorological parameters(pressure,temperature,relative humidity).All supplementary information was recorded with 1 s resolution.The temporally highly resolved measurements allow a detailed analysis of the mercury concentration inside the plume.Inside the plume we found GEM concentrations of up to 10 ng/m?.We will show a tight correlation between GEM and SO2(R?=0.87),allowing to estimate the mercury emission from that modern power plant.In the “AMAP/UNEP geospatially distributed mercury emissions dataset 2010v1” the speciated mercury emissions from combustion in power plants are split to 50%GEM,40%GOM,and 10%particle bound mercury(PBM).From the analysis of the denuder samples we estimated that only less than 2%of the emitted mercury was GOM.Hence,we conclude that the emission of GOM from such modern power plants is strongly overestimated in the AMAP/UNEP dataset.