Aerosol Properties and Processes in the Eastern North Atlantic

JIAN WANG, Guangjie Zheng, Yang Wang, Meinrat O. Andreae, Michael Jensen, Daniel Knopf, Chongai Kuang, Alexander Laskin, Alyssa Matthews, Fan Mei, Ryan Moffet, Arthur J. Sedlacek, John Shilling, Amy P. Sullivan, Jason Tomlinson, Janek Uin, Daniel Veghte, Rodney J. Weber, Rob Wood, Maria Zawadowicz, Washington University in St. Louis

     Abstract Number: 500
     Working Group: Remote and Regional Atmospheric Aerosol

Abstract
With their extensive coverage, marine low clouds strongly impact global climate. Presently, the response of marine low clouds to changes of atmospheric aerosols remains a major source of uncertainty in climate simulations. The Eastern North Atlantic (ENA) is a region of persistent but diverse subtropical marine boundary layer clouds, whose albedo and precipitation are highly susceptible to perturbations in aerosol properties. In addition, ENA is periodically impacted by continental aerosols from North America, making it an excellent location to study the cloud condensation nuclei (CCN) budget in a remote marine region periodically perturbed by anthropogenic emissions.

The aerosol properties and the processes that drive the CCN population in the ENA are examined by combining the airborne measurements during the Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA) campaign and long-term observations at a ground site on Graciosa Island in the Azores. We show that new particle formation occurs regularly in the upper part of remote marine boundary layer (MBL) following the passage of cold fronts, and this new particle formation likely represents a substantial source of CCN in the MBL. The entrainment of free troposphere (FT) air is a major source of Aitken mode particles in the MBL, which can subsequently grow and reach CCN size range. We found that secondary organics represent important or even the dominant condensing species during ~80% of particle growth events observed during the ACE-ENA. The condensational growth of nucleation/Aitken mode particles represents a major source of CCN in the MBL, and it may be underestimated in global models. Elevated accumulation mode particle concentration was observed in the lower FT during summer and is attributed to more frequent long-range transport of continental emissions from North America. The variations of the aerosol properties and processes with season and synoptic conditions are also examined.