Preprints
https://doi.org/10.5194/acp-2020-893
https://doi.org/10.5194/acp-2020-893

  20 Oct 2020

20 Oct 2020

Review status: this preprint is currently under review for the journal ACP.

Properties and emission factors of CCN from biomass cookstoves – observations of a strong dependency on potassium content in the fue

Thomas Bjerring Kristensen1, John Falk1, Robert Lindgren2, Christina Andersen3, Vilhelm B. Malmborg3, Axel C. Eriksson3, Kimmo Korhonen4, Ricardo Luis Carvalho2,5, Christoffer Boman2, Joakim Pagels3, and Birgitta Svenningsson1 Thomas Bjerring Kristensen et al.
  • 1Department of Physics, Lund University, 22100, Lund, Sweden
  • 2Thermochemical Energy Conversion Laboratory, Department of Applied Physics and Electronics, Umeå University, 90187, Umeå, Sweden
  • 3Ergonomics and Aerosol Technology, Lund University, 22100, Lund, Sweden
  • 4Department of Applied Physics, University of Eastern Finland, 70211, Kuopio, Finland
  • 5Centre of Environment and Marine Studies, University of Aveiro, 3810-193 Aveiro, Portugal

Abstract. Residential biomass combustion is a significant source of aerosol particles on regional and global scales influencing climate and human health. The main objective of the current study was to investigate the properties of cloud condensation nuclei (CCN) emitted from biomass burning of solid fuels in different cookstoves mostly of relevance to Sub-Saharan East Africa.

The traditional 3-stone fire (3S) and a rocket stove (RS) were used for combustion of wood logs of sesbania (ses) and casuarina (cas) with birch (bir) used as a reference. A natural draft (ND) and a forced draft (FD) pellet stove were used for combustion of pelletized sesbania and pelletized Swedish softwood (sw) alone or in mixtures with pelletized coffee husk (ch), rice husk (rh) or water hyacinth (wh). The CCN activity and the effective density were measured for particles with mobility diameters of ∼65, ∼100 and ∼200 nm, respectively, and occasionally for ∼350 nm particles. Particle number size distributions were measured online with a fast particle analyzer. The chemical composition of the fuel ash was measured by application of standard protocols.

The average particle number size distributions were by number typically dominated by an ultrafine mode, and in most cases a soot mode was centered around a mobility diameter of ∼150 nm. The CCN activities decreased with increasing particle size for all experiments and ranged in terms of the hygroscopicity parameter, κ, from ∼0.1 to ∼0.8 for the ultrafine mode and from ∼0.0 to ∼0.15 for the soot mode. The CCN activity of the ultrafine mode increased with increasing combustion temperature for a given fuel, and it typically increased with increasing potassium concentration in the investigated fuels. The primary CCN and the estimated particulate matter (PM) emission factors were typically found to increase significantly with increasing potassium concentration in the fuel for a given stove. In order to link CCN emission factors to PM emission factors, knowledge about stove technology, stove operation and the inorganic fuel ash composition is needed. This complicates the use of ambient PM levels alone for estimation of CCN concentrations in regions dominated by biomass combustion aerosol, with the relation turning even more complex when accounting for atmospheric ageing of the aerosol.

Thomas Bjerring Kristensen et al.

 
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Thomas Bjerring Kristensen et al.

Thomas Bjerring Kristensen et al.

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Short summary
Residential biomass combustion is a major anthropogenic source of aerosol particles on regional and global scales. Nevertheless, little is known about those aerosol particles' ability to act as cloud condensation nuclei (CCN) and thus influence cloud properties and climate. Our study shows a strong link between the potassium content in the fuel and emissions of CCN for different stove technologies. Previous studies may have underestimated the anthropogenic climate impact of these emissions.
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