10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
South African Biomass Burning Season Aerosols Observed over the Remote Southeast Atlantic Ocean on Ascension Island
Allison Aiken, Paquita Zuidema, Arthur J. Sedlacek, THOMAS WATSON, Stephen Springston, Connor Flynn, Chongai Kuang, Janek Uin, Manvendra Dubey, Los Alamos National Lab
Abstract Number: 1607 Working Group: Remote/Regional Atmospheric Aerosol
Abstract Biomass burning (BB) emissions are a large source of carbon to the atmosphere via particles and gas phase species. 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). 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. During the U.S. DOE ARM field campaign, Layered Atlantic Smoke Interactions with Clouds (LASIC), direct online in situ measurements of aerosol and trace gases were collected continuously on Ascension Island from June 2016 through October 2017 spanning a ~1.5 year period. While low Southern Hemisphere background aerosol and trace gas measurements are observed most of the year that picture changes during the South African BB season.
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). Refractory light absorbing carbon mass concentrations reach 1 µg m-3 during multiday plumes and exceed 25% of the total aerosol submicron mass concentration, contrasting significantly with BB plumes observed over the Southwestern United States (SW US) and South America (Brazil). 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.
Comparison will be made between the aerosol species observed during LASIC versus BB from wildfires measured in the SW US and Brazil. Results from single fuel laboratory studies probed with aerosol mass spectrometry alongside aerosol optical properties will also be presented contrasting near source and far field BB emission profiles. Organic Aerosol (OA) to refractory soot ratios of ~2.4 observed in the BB plumes from South Africa on Ascension Island are much higher than BB emissions sampled from forest fires in the SW US and BB sources in Brazil. The differences observed between BB emissions in different regions highlights the need to further understand the different atmospheric chemistries within the context of the differing background conditions in the two hemispheres, including differences in BB fuel types and combustion conditions.