New Particle Formation Events Can Reduce Cloud Droplets in Boundary Layer Clouds at the Continental Scale

New particle formation (NPF) substantially contributes to global cloud condensation nuclei (CCN), and their climate impacts. Individual NPF events are also thought to increase local CCN, cloud droplet number (CDN), and cloud albedo. High resolution simulations however go against the latter, showing that radiatively important stratiform clouds can experience a systematic and substantial decrease in CDN during and after NPF events. CDN drops because particles too small to act as CCN uptake condensable material, and stunt the growth of particles that would otherwise form droplets. Convective clouds however experience modest increases in CDN-consistent with established views on the NPF-cloud link. Together, these results reshape our conceptual understanding of NPF impacts on clouds, as the newly discovered duality of responses would drive cloud systems in a fundamentally different manner than thought.|Most studies assume that cloud condensation nuclei (CCN) changes from new particle formation (NPF) events directly reflect cloud droplet number (CDN) responses in clouds and ignore the growth of pre-existing particles and their contribution to CCN. High resolution state-of-the-art simulations over Europe portray that while convective clouds experience modest increases in CDN, the radiatively important stratiform clouds may present a systematic and substantial decrease in droplet number during and after new particle formation (NPF) events. Consequently, it is evident that NPF exhibits a duality in response-which depending on the local conditions may vitally change the manner in which cloud systems may respond.|New particle formation (NPF) events have always been thought to increase the concentration of particles that form cloud droplets thus always lead to climate cooling tau hrough high resolution modeling it is showed that stratiform clouds influenced by NPF events may experience systematic reductions in droplet leading to local warming from reductions in cloud albedo, while droplet number is always enhanced in convective cloudsThese effects combined could bear important impacts on cloud properties and structure following NPF events