Fig. 3

Cloud droplet number concentration response Δ_CDNC to the surface phase as a function of organic mass fraction and parcel updraft velocity. Δ_CDNC at 200 m above cloud base, as a function of the fixed updraft velocity and organic mass fraction for: a, b Marine (MA) simulations setting accumulation mode concentrations N₂ = 30 cm⁻³ (corresponding to pristine marine accumulation mode, as observed during the NUM event¹⁶) and N₂ = 135 cm⁻³, respectively. c–d Boreal (HYY) with N₂ = 160 cm⁻³ and N₂ = 540 cm⁻³, respectively. Blue and green markers indicate base MA and HYY simulation cases. Dotted boxes outline the regions of the parameter planes associated with typical environmental conditions (Table 2). Accumulation mode concentrations N₂ in panels a and c correspond to lower bounds for the studied environments^16,31, and those in b and d to average values. Dotted curves show the Δ_CDNC = 10% isoline. Dashed curves illustrate the environment specific Δ_α = 5% isolines, i.e., Δ_CDNC = 25, and 28%, respectively for MA and HYY, determined from the Schwartz and Slingo approximation⁶⁴