Fig. 4. Activation of Aitken mode particles in fog.

a Particle size distribution, visibility, particle concentrations in two different size ranges (37–70 and 70–900 nm, representing the larger tail of the Aitken mode and the accumulation mode, respectively) and the total droplet residual concentration (the solid line is the 10-min median and the shaded area the interquartile range, IQR). Grey shaded areas indicate fog periods. b Median (solid line) and IQR (shaded area) particle and residual size distribution for the four different fog periods during the event. The cloud residuals distribution is based on measurements with a differential mobility particle sizer (DMPS) behind a counter flow virtual impactor inlet.