Abstract

Cloud modifications due to aerosol are still the largest uncertainty on total anthropogenic radiative forcing in global climate models. A large part of this uncertainty is related to the number and spatial distribution of cloud condensation nuclei (CCN) in the global atmosphere. Aerosol from new particle formation (NPF) may account for more than 50% of CCN in global low-level clouds, yet the processes that form, grow and remove these particles are under-constrained. This is particularly true in remote regions, where aerosol from NPF are more likely to influence cloud properties and thus global radiative balance.

Between 2016 and 2018 we flew a substantial aerosol payload over the remote Pacific and Atlantic oceans (86S – 83N) on the NASA Atmospheric Tomography Mission (ATom). The flights were conducted once in each of the four seasons, with constant profiling between 0.2 and 12 km altitude. We measured aerosol size distributions from 3 nm to 930 m in diameter, as well as single particle and bulk aerosol chemical composition.

We present analysis of the role of NPF in the remote atmosphere, including the location, frequency and seasonality of NPF occurring in the free troposphere and boundary layer. In areas where our measurements show a clear link between NPF and production of CCN , we compare our observations to global chemistry-climate models to asses model skill in representing these aerosol and their effect on global radiative balance.