Abstract

This study characterizes single particle aerosol composition from filters collected during the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) and CLoud–Aerosol–Radiation Interaction and Forcing: Year 2017 (CLARIFY-2017) campaigns. In particular the study describes aged biomass burning aerosol (BBA), its interaction with the marine boundary layer and the influence of biomass burning (BB) air on marine aerosol. The study finds evidence of BBA influenced by marine boundary layer processing as well as sea salt influenced by BB air. Secondary chloride aerosols were observed in clean marine air as well as in BB-influenced air in the free troposphere. Higher volatility organic aerosol appears to be associated with increased age of biomass burning plumes, and photolysis may be a mechanism for this increased volatility. Aqueous processing and interaction with the marine boundary layer air may be a mechanism for the presence of sodium on many aged potassium salts. By number, biomass burning potassium salts and modified sea salts are the most observed particles on filter samples. These results suggest that atmospheric processing such as photolysis and cloud processing, rather than BB fuel type, has a major role in the elemental composition and morphology of aged BBA.

Highlights

  • With Africa producing almost a third of the Earth’s biomass burning aerosol (BBA) (Roberts et al, 2009), two aircraft campaigns, ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) and CLoud–Aerosol–Radiation Interaction and Forcing: Year 2017 (CLARIFY-2017) were focused on understanding African biomass burning aerosol interaction with clouds and radiation in the southeast Atlantic (Haywood et al, 2021; Redemann et al, 2021)

  • An example of this is the low single scattering albedo in the boundary layer compared to the free troposphere (Zuidema et al, 2018; Pistone et al, 2019). Both campaigns report that a more detailed aerosol process-level understanding including the properties of black carbon, organic carbon and inorganic compounds and how they vary as a function of mixing state and altitude is needed, as is knowledge of properties of the aerosol as they age from emission to deposition and the degree of mixing of BBA into the marine boundary layer (MBL) (Haywood et al 2021; Redemann et al 2021)

  • Our main questions are as follows: (1) what are the aerosols in the region and do CLARIFY and ORACLES aerosol differ from each other based on differences in BB plume age, (2) what are the are differences observed between MBL and FT

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Summary

Introduction

With Africa producing almost a third of the Earth’s biomass burning aerosol (BBA) (Roberts et al, 2009), two aircraft campaigns, ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) and CLoud–Aerosol–. Pósfai et al (1995) performed TEM analysis of marine aerosol as part of the Atlantic Stratocumulus Transition Experiment/ marine Aerosol and Gas Exchange (ASTEX/MAGE) campaign and found that polluted continental air affected sea salt aerosol processing, heterogeneity, and mixing with sulfates and nitrates. With both biomass burning salts and marine salts being major contributors to aerosol in the southeast Atlantic region, a technique that can detect salts is important to accurately represent the aerosol in the region. Our main questions are as follows: (1) what are the aerosols in the region and do CLARIFY and ORACLES aerosol differ from each other based on differences in BB plume age, (2) what are the are differences observed between MBL and FT aerosol, (3) what are the mixing states of the aerosol, (4) what are the proposed processes which have acted on the aerosol

Filter Sampling
Transmission Electron Microscopy – Energy Dispersive X-Ray Analysis (TEM-EDX)
Back-trajectory analysis
Aerosol Mass Spectrometer and Single Particle Soot Photometer
Overview of observations
Aerosol classifications
Organic Aerosol
Potassium salts and black carbon
Marine aerosol
Marine boundary layer and aqueous phase processing
Elemental mixing in individual particles
Conclusions
Full Text
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