Colloquium: Dr. Kevin Sanchez, NASA

Biogenic sources and meteorological processes influence cloud condensation nuclei (CCN) in the clean marine atmosphere, but few measurements exist to constrain climate model simulations of their importance. Here we utilize extensive measurements from the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES), an interdisciplinary investigation to improve understanding of Earth's ocean ecosystem-aerosol-cloud system. Four NAAMES field campaigns were conducted in the western subarctic Atlantic between November 2015 and April 2018, with each campaign targeting specific seasonal events in the annual plankton cycle and consisted of both ship and aircraft-based measurements. Key measurements and model data utilized here include individual particle chemical composition, FLEXible PARTicle (FLEXPART) Lagrangian particle dispersion model back trajectories, and satellite derived variables related to phytoplankton production and abundance. In addition, measured particle and cloud properties are analyzed along with meteorological parameters to identify processes influencing the observed variability. Our results show a clear seasonal difference in the marine CCN budget and coupled meteorological influences, illustrating how important phytoplankton-produced emissions are for CCN in the North Atlantic. The chemical composition of individual atmospheric aerosol particles shows two types of secondary sulfate-containing particles in clean marine air masses that dominate the seasonal differences with higher CCN concentrations during the phytoplankton blooming period. We also find that correlations between some aerosol measurements with satellite-measured and modeled variables increase when weighted by the area covered by back trajectories. This indicates that biological and meteorological processes over the air mass history are influential for measured particle properties and that using only spatially coincident data would miss correlative connections that are lagged in time. In particular, the marine non-refractory organic aerosol mass correlates with modeled marine net primary production when weighted by 5-day air mass trajectory residence time (r=0.62). In a case study, variable meteorological conditions between these two adjacent trajectories resulting from differences in the local sea surface temperature in the Labrador Current and surrounding waters, alter the stability of the marine atmospheric boundary layer and greatly influence downwind particle and cloud properties. One trajectory carried particles through a cold-air outbreak, resulting in a decrease in accumulation mode particle concentration (−42 %) and cloud droplet concentrations, while the other remained outside of the cold-air outbreak and experienced an increase in accumulation mode particle concentrations (+62 %). This study provides observational evidence for connections between marine aerosols and underlying ocean biology through complex secondary formation processes, emphasizing the need to consider air mass history and meteorological influences in future analyses.