Adiabatic cloud parcel model simulations

We used an adiabatic cloud parcel model^42,43 to calculate the number of activated cloud droplets and different predefine updraft velocities at SMEAR II. For the calculations we assume that all organic compounds (including HOM) are fully water soluble at the point of cloud droplet activation. As input we used the modelled aerosol particle properties in the surface layer from the CTRL, NoNPF and NoHOM runs from the periods 15–24 May 2013 and 15 April to 5 May 2014. The air parcels were assumed to start at the surface (0 m) with an initial relative humidity (RH) of 95% and rise to an altitude of 500 m with fixed predefined updraft velocities of 0.01, 0.02, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2.0, 3.0, 5.0 or 10 m s⁻¹. With this setup the air gets supersaturated (RH > 100%) with respect to water vapour at ~115 m altitude and a fraction of the particles (the CCN) gets activated into cloud droplets. Depending on the updraft velocity the maximum cloud supersaturation (SS_max) is reached within a few metres to a few tens of metres above the cloud base (see Supplementary Fig. ¹³).