Giant aerosol particles, i.e., those with diameters larger than 1 um, are similar in size to the newly formed cloud droplets but cannot reach their theoretical equilibrium size within the activation timescale due to kinetic limitation. It is therefore challenging to incorporate detailed and accurate representations of such particles in atmospheric models.

In this study, we assessed the impacts of giant cloud condensation nuclei (GCCN) on radiation, liquid cloud and precipitation using the U.S. Department of Energy’s Energy Exascale Earth System Model version 2(E3SMv2). Firstly, we used a GCCN parameterization that dignoses the abundance and physical properties of giant particles in the 4-mode version of the Modal Aerosol Module (MAM4) and allowed these giant aerosol particles to be activated directly to form drizzle droplets with different sizes. Through this approach, we found by activating GCCN to rain droplets with size of 25 um, liquid water path decreased -5.65% globally. The decrease is more pronounced over the mid-latitudes, while the changes over the tropics are comparatively smaller. This zonal variation change makes the simulated liquid water path more consistent with the satellite observations. Further evaluation shows that this parameterization also improves model's ability to represent positive correlation between surface rain rates and coarse mode concentration at regions with lower precipitation rates. We applied another approach to account for the giant aerosol inertial limitations by removing these large particles before activation. Preliminary findings suggest that the deactivation of giant aerosols leads to a decrease in cloud-borne coarse number concentration, but more Aitken mode particles are activated. Thus, it remains critical to incorporate the treatment of GCCN processes in Earth System Models for better representations of clouds, radiation, and aerosol in the climate system.