Two MOS scenes recorded in March 1998 over the region north of the canary island has been analysed in terms of the microphysical structure. The retrieved optical thickness, geometrical thickness and cloud top pressure indicate, that in both scenes, a boundary layer stratocumulus is observed. The remarkable difference in the retrieved cloud droplet concentration can be validated with back-trajectory calculations: The airmass in the March 24 example is most likely affected by pollution from the European continent. This leads to the strong enhancement of droplet number concentration as observed with remote sensing using MOS.

	March, 4th 1998	March, 24th 1998
Geometrical thickness
Cloud top pressure
Droplet number concentration
Back-trajectories