Boundary Layer Ambient Aerosols on Ascension Island during LASIC: Biomass Burning Season versus Background Conditions
Poster PDF
Authors
Allison C Aiken — Los Alamos National Laboratory
Paquita Zuidema — University of Miami
Arthur J Sedlacek — Brookhaven National Laboratory
Thomas B. Watson — Brookhaven National Laboratory
Stephen R. Springston — Brookhaven National Laboratory
Connor J. Flynn — University of Oklahoma School of Meteorology
Adeyemi A Adebiyi — University of Miami
Chongai Kuang — Brookhaven National Laboratory
Janek Uin — Brookhaven National Laboratory
Manvendra K. Dubey — Los Alamos National Laboratory
Kim L. Nitschke — Los Alamos National Laboratory
Category
ARM field campaigns – Results from recent ARM field campaigns
Description
Ascension Island is located 8 degrees South of the Equator and 15 degrees West Longitude in the middle of the South Atlantic Ocean, at least 1000 miles from any major shoreline and closest to the continent of Africa. While low Southern Hemisphere background aerosol and trace gas measurements are observed most of the year, that picture changes during the South African Biomass Burning (BB) season. BB emissions are a large source of carbon to the atmosphere via particles and gas phase species and with a potential rise in drought and extreme events in the future, these numbers are expected to increase. From approximately June-October every year, the plume of South African BB emissions, the largest BB source in the world, are advected West and are known to impact both the boundary layer and free troposphere at Ascension Island (Zuidema et al., 2016). During the U.S. DOE ARM field campaign, Layered Atlantic Smoke Interactions with Clouds (LASIC), aerosol and trace gas measurements were collected continuously from June 2016 through October 2017 over a ~1.5 year period. Two BB seasons are contrasted with the near pristine background conditions during the campaign from the ARM Aerosol Mobile Facility 1 (AMF1) and Mobile Aerosol Observing System (MAOS). Numerous direct in situ aerosol and trace gas measurements are presented, e.g. submicron non-refractory chemical composition (Organics, Sulfate, Nitrate, Ammonium, Chloride), refractory soot, PM1 and PM10 aerosol absorption and scattering, carbon monoxide (CO), etc. Aerosol and trace gas signatures are investigated along with backtrajectories to identify sources. Carbonaceous aerosols emitted with gas-phase CO are used to determine particulate emission ratios along with intrinsic and extrinsic aerosol properties. Refractory soot mass concentrations reach 1 µg m-3 during multiday plumes and exceed 25% of the total aerosol submicron mass concentration. Organic Aerosol (OA) to refractory soot ratios of ~2.4 in the plume are much higher than previously observed BB emissions in the Northern Hemisphere from forest fires in the US and also BB sources in Brazil. The differences observed between BB emissions in the Northern versus Southern Hemispheres highlights the need to understand the different atmospheric chemistries within the context of the differing background conditions of the two hemispheres.
