Plume-exit modeling to determine cloud condensation nuclei activity of aerosols from residential biofuel combustion

Abstract

Abstract. Residential biofuel combustion is an important source of aerosols and gases in the atmosphere. The change in cloud characteristics due to biofuel burning aerosols is uncertain, in part, due to the uncertainty in the added number of cloud condensation nuclei (CCN) from biofuel burning. We provide estimates of the CCN activity of biofuel burning aerosols by explicitly modeling plume dynamics (coagulation, condensation, chemical reactions, and dilution) in a young biofuel burning plume from emission until plume exit, defined here as the condition when the plume reaches ambient temperature and specific humidity through entrainment. We found that aerosol-scale dynamics affect CCN activity only during the first few seconds of evolution, after which the CCN efficiency reaches a constant value. Homogenizing factors in a plume are co-emission of semi-volatile organic compounds (SVOCs) or emission at small particle sizes; SVOC co-emission can be the main factor determining plume-exit CCN for hydrophobic or small particles. Coagulation limits emission of CCN to about 10 16 per kilogram of fuel. Depending on emission factor, particle size, and composition, some of these particles may not activate at low supersaturation (s sat ). Hygroscopic Aitken-mode particles can contribute to CCN through self-coagulation but have a small effect on the CCN activity of accumulation-mode particles, regardless of composition differences. Simple models (monodisperse coagulation and average hygroscopicity) can be used to estimate plume-exit CCN within about 20 % if particles are unimodal and have homogeneous composition, or when particles are emitted in the Aitken mode even if they are not homogeneous. On the other hand, if externally mixed particles are emitted in the accumulation mode without SVOCs, an average hygroscopicity overestimates emitted CCN by up to a factor of 2. This work has identified conditions under which particle populations become more homogeneous during plume processes. This homogenizing effect requires the components to be truly co-emitted, rather than sequentially emitted.

Properties and emission factors of cloud condensation nuclei from biomass cookstoves – observations of a strong dependency on potassium content in the fuel

“…We speculate that the easily combustible sw pellets with higher burn rate in the FDS resulted in quenching of the flame on the bottom of the pot, leading to enhanced soot emissions, while the pellet mixtures with relatively lower burn rate were likely to result in relatively lower flame height and no quenching of the flame inside the FDS, resulting in low soot emissions. In general, the particle number size distributions compare well with previously published results for comparable experiments (Just et al, 2013;Shen et al, 2017;Mitchell et al, 2019).…”

“…The emission factors of CCN for wildfire biomass combustion have been estimated to be on the order of 0.8 × 10 15 to 1.7×10 15 kg −1 relative to the dry mass of various fuels and assuming a supersaturation of 0.5 % (Andreae, 2019). Mena et al (2017) modelled the CCN properties of a residential biomass combustion plume, and they concluded that coagulation limits the CCN emission factor for a supersaturation of 1.0 % to a maximum of 10 16 per kilogram of fuel.…”

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

“…The emission factors of CCN for wild fire biomass combustion have been estimated to be at the order of 0.8•10 15 to 1.7•10 15 kg −1 relative to the dry mass of various fuels and assuming a supersaturation of 0.5% (Andreae, 2019). Mena et al (2017) modeled the CCN properties of a residential biomass combustion plume and they concluded that coagulation limits the CCN emission factor for a supersaturation of 1.0% to a maximum of 10 16 per kg of fuel.…”