Aged Biomass Burning Aerosol: BC-dominated Absorbing Plumes Observed at Ascension Island within the Marine Boundary Layer during LASIC
Poster PDF
Authors
Allison C Aiken — Los Alamos National Laboratory
Paquita Zuidema — University of Miami
Thomas B. Watson — Brookhaven National Laboratory
Arthur J Sedlacek — Brookhaven National Laboratory
Janek Uin — Brookhaven National Laboratory
Stephen R. Springston — Brookhaven National Laboratory
Manvendra K. Dubey — Los Alamos National Laboratory
Francesca Gallo — NASA Langley
James Edward Lee — Los Alamos National Laboratory
Dian Romonosky — Los Alamos National Laboratory
Category
ARM field campaigns – Results from recent ARM field campaigns
Description
Biomass burning (BB) aerosol are complex and dynamic, covering a vast range of optical properties and chemical compositions. BB aerosol includes refractory black carbon, brown carbon, and non-absorbing organic carbon species that can be internally and externally mixed. During the Layered Atlantic Smoke Interactions with Clouds (LASIC) Campaign, aerosol and trace gas measurements were collected continuously from June 2016 through October 2017. Highly absorbing BB aerosol were observed by the ARM Aerosol Observing System (AOS) with absorption coefficients up to 30 Mm-1 during the South African biomass burning season from June to August over two seasons. Black carbon mass concentrations account for up to 25% of the submicron mass during these events. From the Aerosol Chemical Speciation Monitor (ACSM) within the AOS at LASIC it is evident that organic aerosol dominates the submicron composition at ~65% of the total mass. However, no BrC is apparent in the optical property data as the Absorption Angstrom Exponent (AAE) during the plumes is dominated by BC with an AAE of ~1.0. The non-refractory organic chemical composition also does not have typical BB signals in the ACSM data (e.g. levoglucosan fragment ions). LASIC organic aerosol is highly oxidized/aged with an Oxygen-to-Carbon ratio of ~1 and an Organic-Mass-to-Organic-Carbon ratio of 2.4, consistent with photochemical aging over timescales of 1-2 weeks. To further investigate the properties and processes that the South African BB plume has experienced in the atmosphere we combine our analysis of chemical and optical property data with physical properties and water uptake information from the AOS to understand the BB plume processing. Positive Matrix Factorization of the ACSM data is used to identify organic aerosol signatures during the two BB seasons and the interannual differences between 2016 and 2017. LASIC organic aerosol signatures are compared with fresh and aged sources sampled with the Soot Particle Aerosol Mass Spectrometer (SP-AMS) at LANL that can directly identify Nitrogen-containing species. Plumes sampled in the SW US with the SP-AMS with up to ~ 1 week atmospheric aging timescales during transport from the Pacific Northwest will be compared with LASIC as well as organic aerosol signatures from fresh BB emissions from nearby BB sources and controlled laboratory studies to elucidate the differences between fresh and aged BB physicochemical and optical signatures for model parameterization.
