Ion mediated nucleation and anthropogenic aerosol indirect radiative forcing

A clear understanding of particle formation mechanisms is critical for assessing aerosol indirect radiative forcing (IRF) and associated climate feedback processes. Recent studies reveal the importance of ion-mediated nucleation (IMN) in generating new particles and cloud condensation nuclei (CCN) in the atmosphere. The IMN scheme has been implemented in two widely used community models (CAM5/MAM3 and GEOS-Chem/APM). Here we employ the two models to assess the effect of anthropogenic emissions on the aerosol IRF. Our model simulations, with new particle formation rates calculated by the IMN scheme, show a significant impact of anthropogenic emissions on global CCN abundance, cloud properties, and cloud radiative forcing. The total aerosol indirect radiative forcing based on CAM5/MAM3 is-1.81 W m−2. The first aerosol IRF based on GEOS-Chem/APM is −0.69 W m−2.