Cold Air Outbreaks Promote New Particle Formation Off the US East Coast

New particle formation (NPF) is the dominant contributor to total particle number concentration and plays an important role in the cloud condensation nuclei budget. Airborne data from Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) are used to address seasonal NPF statistics and factors related to NPF in and around clouds. Higher ratios of particle concentrations greater than 3 versus 10 nm (N-3/N-10) were mainly observed above boundary layer cloud tops during winter as compared to summer. Cold dry air and low aerosol surface area concentration facilitate NPF over the ACTIVATE region; these conditions are especially prevalent during flights coinciding with cold air outbreaks.