Plume-exit modeling to determine cloud condensation nuclei activity of
aerosols from residential biofuel combustion
Francisco Mena1, Tami C. Bond1, and Nicole Riemer21Department of Civil and Environmental Engineering, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA 2Department of Atmospheric Sciences, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
Received: 26 Jan 2017 – Accepted for review: 01 Feb 2017 – Discussion started: 03 Feb 2017
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 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 1016 per kg of fuel. Depending on emission factor, particle size, and composition, some of these particles may not activate at low ssat. 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.
Mena, F., Bond, T. C., and Riemer, N.: Plume-exit modeling to determine cloud condensation nuclei activity of
aerosols from residential biofuel combustion, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-67, in review, 2017.