PNNL

Abstract

Advancing knowledge of cloud condensation nuclei (CCN) characteristics has important consequences for weather and climate, making field observations vital. This work characterizes CCN using airborne data from the Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) spanning areas from the U.S. East Coast to Bermuda between November 2020 through June 2022. CCN concentrations at the most commonly sampled supersaturation (SS; 0.37–0.43%) ranged from medians of 652 cm-3 in summer to 460 cm-3 in winter, dropping to 310 cm-3 near Bermuda in June. The median observed hygroscopicity parameter (?) varied from 0.19–0.21 across winter, spring, and summer and increased to 0.97 near Bermuda. Using speciated composition and number size distribution measurements, we predict CCN concentrations with those measured at SS ranging from 0.16–0.72%, revealing that the cumulative median predicted-to-observed CCN ratio was 1.08, with the best agreement in spring (1.10) and the largest discrepancies near Bermuda (0.89). CCN overpredictions were associated with biomass burning events in summer, while CCN were largely underestimated near Bermuda due to higher observed ? than assumed for inorganics. This study provides key insights into CCN activity over the northwest Atlantic, capturing the transition from polluted to remote oceanic environments.