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Major secondary aerosol formation in southern African open biomass burning plumes


Open biomass burning contributes significantly to air quality degradation and associated human health impacts over large areas. It is one of the largest sources of reactive trace gases and fine particles to Earth’s atmosphere and consequently a major source of cloud condensation nuclei on a global scale. However, there is a large uncertainty in the climate effect of open biomass burning aerosols due to the complexity of their constituents. Here, we present an exceptionally large dataset on southern African savannah and grassland fire plumes and their atmospheric evolution, based on 5.5 years of continuous measurements from 2010 to 2015. We find that the mass of submicrometre aerosols more than doubles on average, in only three hours of daytime ageing. We also evaluate biomass burning aerosol particle size distributions and find a large discrepancy between the observations and current model parameterizations, especially in the 30–100 nm range. We conclude that accounting for near-source secondary organic aerosol formation and using measurement-based size distribution parameterizations in smoke plumes is essential to better constrain the climate and air quality effects of savannah and grassland fires.

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V.V. is beneficiary of an AXA Research Fund postdoctoral grant. Financial support by North-West University, South Africa and Academy of Finland (grant no. 307331) is gratefully acknowledged.

Author information

J.P.B., M.J. and P.G.v.Z. carried out the measurements at Welgegund while V.V. and M.A. contributed to measurement design. M.D.M. carried out aerosol dynamic simulations. V.V. analysed data and wrote most of the paper. All authors commented on the manuscript during the writing process.

Competing interests

The authors declare no competing interests.

Correspondence to Ville Vakkari.

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Fig. 1: Savannah and grassland PM1 emissions decrease with increasing combustion efficiency.
Fig. 2: Secondary aerosol formation is faster in more smouldering plumes.
Fig. 3: Majority of biomass burning smoke observations at Welgegund have potential for significant PM1 enhancement.
Fig. 4: Aitken mode size distribution is poorly represented by current parameterizations30,31.