The Flexible Particle Dispersion Model (FLEXPART) is used in order to acquire residence times over geographic grid cells (sensitivity). These indicate how sensitive the measurements at a station are to emissions occurring at each geographic grid cell. FLEXPART runs account for grid scale wind as well as for turbulent and mesoscale wind fluctuations. Drift correction, to prevent accumulation of the released computational particles, and density correction, to account for the decrease of air density with height, were both applied. A twenty-day backward run with the release of 40000 air parcels every 3 h beginning from HAC station is displayed. Residence times in each grid cell, for a height from 0 to 100 m above ground level (agl), were acquired.