Examining the Impacts of Aerosol Emission Processes on CCN Activation over the North Atlantic Using Two Earth System Models

Marine boundary layer (MBL) clouds play an important role in the climate system because their strong ability to affect radiative budget by reflecting solar radiation. The macro- and microphysical properties of MBL clouds are very sensitive to the cloud condensation nuclei (CCN) concentrations and hence to the aerosol properties. Here we use the Energy Exascale Earth System Model (E3SMv1) and the Community Earth System Model (CESMv2.1) with nudging winds method to study the impact of different aerosol treatments on CCN budget and radiative budget. The modeled aerosol and CCN fields are compared against the aircraft measurements during the Atmospheric Radiation Measurement (ARM) Aerosol and Cloud Experiments in the Eastern North Atlantic campaigns (ACE-ENA) and surface observations at the ARM ENA site in Azores from 2014 to 2018.

Our results show that both models reasonably capture the clear CCN seasonal cycle at surface with a peak in July. In addition, E3SM successfully reproduce the vertical profiles of CCN, while CESM slightly underestimates the magnitude. However, E3SM significantly overpredicts aerosol number concentration in size range of 50-600 nm. By comparing the default E3SM experiment with the sensitivity experiment in which we set the secondary organic aerosol gases (SOAG) emission at the surface, we find that this overestimation is largely related to treatment of SOA emissions. Finally, we examine the radiative effects associated with different treatments of aerosol emissions. We find that setting SOAG emissions at surface can cause a 0.91 W/m² warming effect, while 1.18 W/m² warming effect if we turned off DMS emissions.