Ultra-clean marine boundary layers over the Southeast Atlantic

Poster PDF

Description

The Southeast Atlantic features both one of the largest persistent stratocumulus decks in the world and the strong seasonal influence of aerosol particles generated in African biomass burning. Understanding the meteorological, physical and chemical drivers of variability in boundary layer aerosol particle number is thus crucial for determining the extent of aerosol-cloud interactions and associated radiative effects in this region. The deployment of an ARM Mobile Facility to Ascension Island (ASI) as part of the Layered Atlantic Smoke Interactions with Clouds (LASIC) campaign is providing new insight into these processes. There is a pronounced seasonal cycle in the variability of boundary layer aerosol at ASI, with months featuring intrusions of biomass burning smoke also often featuring extreme depletion of accumulation mode (~ CCN-sized) particles. We study 38 of these ‘ultra-clean’ days throughout the LASIC deployment in 2016 and 2017, with a particular focus on understanding the causes of accumulation mode collapse and their implications for the full aerosol size distribution. For example, we document and analyze several cases of new particle formation under ultra-clean conditions. Coupled with other studies of heavy smoke influence, this work will hopefully contribute to a more comprehensive understanding of two-way aerosol-cloud interactions over the climatically important SE Atlantic.