3 Years of Airborne Observations over the South East Atlantic: A Review of African Biomass Burning Aerosol Physiochemistry Measurements in the Free Troposphere and Marine Boundary Layer
Abstract
During three consecutive years of NASA ORACLES airborne missions (2016-18), biomass burning (BB) advected from the African continent out over the South East Atlantic was intensively studied to better understand the role of BB aerosol in the regional radiation budget but also to discern its effect from natural aerosol on underlying Stratocumulus (Sc) clouds in the marine boundary layer (MBL). Because of its particle size and vast quantities BB aerosol once entrained into the MBL from the Free Troposphere (FT) are highly effective as cloud condensation nuclei (CCN) impacting cloud microphysical properties and as such the Sc deck's radiative budget. This work reviews characteristic in-plume aerosol size distribution information (ambient and heated to 360oC) observed during the campaigns as well as aerosol chemistry measurements obtained with a Single Particle Soot Photometer (SP2) and an Aerosol Mass Spectrometer (AMS). BB plume history is inferred from AMS-derived organic aerosol oxidation state in conjunction with Weather Research and Forecasting Model estimates of plume age. The FT results are compared to MBL aerosol observations and adjacent Sc cloud properties such as the cloud droplet number concentration. Additionally, aerosol size distributions and chemistry were measured in the cloud occasionally using a Counterflow Virtual Impactor (CVI) inlet sampling exclusively cloud droplet residuals. Employing the CVI cloud droplets are inertially separated from the air and dried in-situ en-route to the aerosol instrumentation. This allows us to study natural and combustion-influenced aerosol that were actually activated as CCN in the Sc deck. These CVI measurements reveal episodic high supersaturation events activating particles in the Aitken mode range. The data also provide insight into mechanisms of precipitation scavenging suggesting the preferred removal of more hygroscopic aerosol in drizzling Sc clouds.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A13H2545F
- Keywords:
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- 0321 Cloud/radiation interaction;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSESDE: 3355 Regional modeling;
- ATMOSPHERIC PROCESSESDE: 3360 Remote sensing;
- ATMOSPHERIC PROCESSES