Particle-phase chemical composition measurements onboard the G-1 research aircraft during the GoAmazon 2014/5 campaign
Poster PDF
Authors
John E Shilling — Pacific Northwest National Laboratory
Mikhail S. Pekour — Pacific Northwest National Laboratory
Ed Fortner — Aerodyne Research, Inc.
Paulo Artaxo — University of Sao Paulo
Suzane Simoes deSa — Harvard University
John Hubbe — Pacific Northwest National Laboratory
Karla Longo — National Institute for Space Research (INPE)
Luiz Augusto Toledo Machado — INPE-CPTEC
Scot T. Martin — Harvard University
Stephen R. Springston — Brookhaven National Laboratory
Jason Tomlinson — Pacific Northwest National Laboratory
Jian Wang — Washington University in St. Louis
Category
ARM field campaigns – Results from recent ARM field campaigns
Description
The Green Ocean Amazon (GoAmazon 2014/5) campaign, conducted in the vicinity of Manaus, Brazil, was designed to study the aerosol lifecycle and aerosol-cloud interactions in both pristine and anthropogenically-influenced conditions. As part of this campaign, the DOE G-1 research aircraft was deployed from February 17 – March 25, 2014 (wet season) and September 6 – October 5, 2014 (dry season) to investigate aerosol and cloud properties aloft. Here, we present results from the G-1 deployments focusing on measurements of the aerosol chemical composition and discussion of aerosol sources and secondary organic aerosol formation and aging.
Organic aerosol (OA) dominate the deployment-averaged chemical composition, comprising 79% of the total mass with sulfate comprising 12%, nitrate 5%, and ammonium 4%. This product distribution was unchanged between seasons, despite the fact that total aerosol loading was significantly higher in the dry season and that regional and local biomass burning was a significant source of organic aerosol mass in the dry, but not wet, season. Similarly, the aerosol chemical composition was acidic, with little difference observed between seasons. However, the organic aerosol was more oxidized in the dry season, with the median of the mean carbon oxidation state increasing from -0.45 in the wet season to -0.02 in the dry season.
We also examine the evolution of the Manaus plume on March 13, 2014, one of the campaign golden days in the wet season. On this flight, we observe a clear increase in OA concentrations in the Manaus plume relative to the background. We also observe a dynamic conversion of hydrocarbon-like organic aerosol (HOA) into oxygenated organic aerosol (OOA) and an increase in the mean oxidation state of the OA over the observed 4-5 hour aging timescale. However, the ratio of excess OA to excess CO (Δorg/ΔCO) averages 31 μg/m3 ppmv-1 and does not increase with aging, in contrast to many studies of the outflow of urban centers that find this quantity increases with aging. A conversion of HOA to OOA mass appears to largely explain the constant Δorg/ΔCO observations. Constant Δorg/ΔCO with plume aging has been observed in many biomass burning plumes, but we are unaware of reports of fresh urban emissions aging in this manner. These observations suggest that SOA formation in the Manaus plume occurs, at least in part, by a different mechanism than observed in urban outflow plumes of other large urban centers.
