Marine boundary layer aerosol in Eastern North Atlantic: seasonal variations and the key controlling processes
Poster PDF
Authors
Guangjie Zheng — Washington University in St Louis
Tamara Pinterich — Brookhaven National Laboratory
Allison C Aiken — Los Alamos National Laboratory
Robert Lesley Bullard — Brookhaven National Laboratory
Edward Luke — Brookhaven National Laboratory
Pavlos Kollias — Stony Brook University
Chongai Kuang — Brookhaven National Laboratory
Stephen R. Springston — Brookhaven National Laboratory
Janek Uin — Brookhaven National Laboratory
Thomas B. Watson — Brookhaven National Laboratory
Robert Wood — University of Washington
Jian Wang — Washington University in St. Louis
Category
ARM field campaigns – Results from recent ARM field campaigns
Description
The response of marine low cloud systems to changes in aerosols represents one of the largest uncertainties in climate simulations. Major contributions to this uncertainty derive from poor understanding of aerosol under natural conditions and the perturbation by anthropogenic emissions. The Eastern North Atlantic Ocean (ENA) is a region of persistent but diverse marine boundary layer (MBL) clouds, and whose albedo and precipitation are highly susceptible to perturbation in aerosol properties. In this study, we examine aerosol properties, trace gas concentrations, and meteorological parameters measured at the ARM ENA site on Graciosa Island since 2014. Aerosol size distribution from 60 nm to 1 μm typically consists of three modes: Aitken (At), Accumulation (Ac) and Sea Spray Aerosol (SSA) modes. Observed CCN number concentrations are in general agreement with the sum of Ac and SSA mode concentrations. The number concentration of SSA mode, mainly driven by sea spray aerosol (SSA) production and precipitation scavenging, is higher in winter and lower during summer. The entrainment of free tropospheric aerosols, including long range transported continental pollution, represents a major source of At and Ac mode particles. In comparison, SSA often contributes to a minor fraction of At and Ac mode number concentrations, with estimated mean annual contribution around 12% and 21%, respectively. For the combined population of At and Ac mode particles, coalescence scavenging represents the major sink, while coagulation of At mode particles with Ac and SSA mode particles and activated droplets inside clouds can also play a role. Higher contribution of entrained free tropospheric aerosol is coincident with stronger precipitation during spring and winter seasons. As a result, At and Ac mode number concentrations exhibit weak seasonal variations, with slightly higher levels during the spring summer seasons.
