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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Sep 2018

Research article | 26 Sep 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

The vertical distribution of biomass burning pollution over tropical South America from aircraft in situ measurements during SAMBBA

Eoghan Darbyshire1, William T. Morgan1, James D. Allan1, Dantong Liu1, Michael J. Flynn1, James R. Dorsey1, Sebastian J. O'Shea1, Douglas Lowe1, Kate Szpek2, Franco Marenco2, Ben T. Johnson2, Stephane Bauguitte3, Jim M. Haywood2,4, Joel F. Brito5,a, Paulo Artaxo5, Karla M. Longo6,b, and Hugh Coe1 Eoghan Darbyshire et al.
  • 1Centre for Atmospheric Science, University of Manchester, Manchester, UK
  • 2Met Office, Exeter, UK
  • 3Facility for Airborne Atmospheric Measurements (FAAM), The University of Cranfield, Cranfield, UK
  • 4CEMPS, University of Exeter, Exeter, UK
  • 5Physics Institute, University of Sao Paulo, Sao Paulo, Brazil
  • 6National Institute for Space Research (INPE), Sao Jose dos Campos, Brazil
  • anow at: Laboratory for Meteorological Physics (LaMP ), University Clermont Auvergne, Aubière, France
  • bnow at: NASA Goddard Space Flight Center and USRA/GESTAR, Greenbelt, MD, USA

Abstract. To reduce the uncertainties in processes driving the vertical distribution of biomass burning pollutants, and thus impacts on regional weather and climate, we present an integrated analysis of vertical profiles of pollutants and meteorological parameters measured on flights during the 2012 South American Biomass Burning Analysis (SAMBBA) field experiment.

During the dry season there were significant contrasts in the composition and vertical distribution of haze between western and eastern regions of tropical South America. Owing to an active or residual convective mixing layer, the aerosol burden was similar from the surface to ~1.5km in the west and ~3km in the east. Black carbon mass loadings were double in the east (1.7µgcm−3) than west (0.85µgcm−3) but aerosol scattering coefficients at 550nm were similar (~120Mm−1), as too were CO surface concentrations (310–340ppb). We attribute these contrasts to the more flaming combustion of Cerrado fires in the east and more smouldering combustion of deforestation and pasture fires in the west. Horizontal wind shear was important in inhibiting mixed layer growth and plume rise, in addition to advecting pollutants from the Cerrado regions into the remote tropical forest of central Amazonia. Optically thin layers above the mixing layer indicates roles for both plume injection and shallow moist convection in delivering pollution to the lower free troposphere. However, detrainment of large smoke plumes into the upper free troposphere was very infrequently observed. Our results reiterate that thermodynamics control the pollutant vertical distribution and thus point to the need for correct model representation so the spatial distribution and vertical structure of biomass burning smoke is captured.

Our observations of relatively large concentrations of aerosol aloft and of CO near surface suggest that there is a greater contribution of pollutants from more complete combustion with altitude. Release of appropriate emissions from the initial more flaming and later residual smouldering phases of a fire at appropriate altitudes may be especially important to ensure models can accurately predict aerosol-radiation, aerosol-cloud and air quality impacts.

Eoghan Darbyshire et al.
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Status: open (until 21 Nov 2018)
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Eoghan Darbyshire et al.
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Short summary
A novel analysis of aerosol & gas phase vertical profiles shows that a marked regional pollution contrast in (a)composition is driven by fire regime, and (b)vertical distribution is driven by thermodynamics. These drivers ought to be well represented in simulations to ensure realistic prediction of biomass burning climate & air quality impacts. Also to this end, we advocate further enquiry into the link between combustion stage, pollution composition and plume injection height hypothesised here.
A novel analysis of aerosol & gas phase vertical profiles shows that a marked regional pollution...