A036-0011
Long-Range Transported Continental Aerosols Increase Observed Cloud Condensation Nuclei in the Eastern North Atlantic

Tuesday, 8 December 2020
Poster
Francesca Gallo1, Uin Janek2, Connor Joseph Flynn3, Stephen R. Springston2, Rob Wood4, Eduardo Brito de Azevedo5, Fan Mei6, Chongai Kuang7 and Allison C Aiken1, (1)Los Alamos National Laboratory, Los Alamos, NM, United States, (2)Brookhaven National Laboratory, Upton, NY, United States, (3)PNNL, Richland, VA, United States, (4)University of Washington Seattle Campus, Seattle, WA, United States, (5)University of Azores, Angra do Heroismo, Portugal, (6)Pacific Northwest National Laboratory, Richland, WA, United States, (7)Brookhaven National Laboratory, Environmental and Climate Sciences Department, Upton, NY, United States
Abstract:
Ambient aerosols interact with clouds by acting as cloud condensation nuclei, affecting cloud radiative properties, lifetime and water content. Remote ocean regions dominated by pristine conditions and low clouds are the most susceptible to changes in aerosol properties. To improve the understanding of aerosol-cloud interactions in marine environment, in 2013, the US DOE established an Atmospheric Radiation Measurement Facility in Eastern North Atlantic (ENA). Through the year, the marine boundary layer aerosol at ENA is occasionally perturbed by entrainment of anthropogenic and natural particles from the free troposphere attributable to continental transports, with consequences on cloud condensation nuclei (NCCN) activities.

Here, we: 1) develop an algorithm that integrates submicron aerosol size distribution, single scattering albedo and black carbon concentration measurements to detect events of long-range continental transport at ENA and extract the regional aerosol baseline; 2) evaluate the impact of continental particles on the CCN budget. During 2017, our algorithm identified 9 events of long-range transported particles (with durations > 24 hours), corresponding to ~ 10% of the year. During transport events dominated by a mixture of dust, and marine aerosols, submicron aerosol number concentrations (Ntot) increased > 108%. The Aitken (Dp > 100 nm) and Accumulation (Dp 100 to 300 nm) modes increased homogeneously, and were accompanied by ~ 135% NCCN (0.1% supersaturation) increments, while the CCN activation fraction (AF) remained constant at 0.25 ± 0.07. Transports of mixtures of marine and continental polluted aerosols caused Ntot increments > 95%, while Ntot increases associated to transport of biomass burning aerosols containing soot were lower (< 26%). In both cases sharp increases in the Ac mode (120 to 264%) and minimal changes in the At mode (> 25% increase in the first case, < 28% decrease in the latter) were observed. NCCN and AF exhibited increases of > 170% and > 40% respectively during the events, indicating that, despite the low hygroscopicity of the transported particles, the high overall concentration of particles in the Ac mode effectively serve as CCN, strongly contributing to the CCN budget at ENA. Measurements from the aircraft overflights will be used to support our findings.

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