Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/gmd-2017-123
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Model description paper
14 Jul 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Geoscientific Model Development (GMD).
A parameterisation for the co-condensation of semi-volatile organics into multiple aerosol particle modes
Matthew Crooks, Paul Connolly, and Gordon McFiggans The School of Earth, Atmospheric and Environmental Science, The University of Manchester, Oxford Road, Manchester, M13 9PL
Abstract. A new parameterisation for cloud droplet activation of multiple aerosol modes is presented that includes the effects of co-condensation of semi-volatile organic compounds (SVOCs). The novel work comes from the dynamic condensation parameterisation that approximates the partitioning of the SVOCs into the condensed phase at cloud base. The dynamic condensation parameterisation differs from equilibrium absorptive partitioning theory by calculating time dependent condensed masses that depend on the updraft velocity. Additionally, more mass is placed on smaller particles than at equilibrium, which is in better agreement with parcel model simulations. All of the SVOCs with saturation concentrations below 1 × 10−3 μg−3 are assumed to partition into the condensed phase at cloud base, defined as 100 % relative humidity, and the dynamic condensation parameterisation is used to distribute this mass between the different aerosol modes. An existing cloud droplet activation scheme is then applied to the aerosol particles at cloud base with modified size distributions and chemical composition to account for the additional mass of the SVOCs. Parcel model simulations have been performed to test the parameterisation with a range of aerosol size distributions, composition and updrafts. The results show excellent agreement between the parameterisation and the parcel model and the inclusion of the SVOCs does not degrade the performance of the underlying cloud droplet activation scheme.

Citation: Crooks, M., Connolly, P., and McFiggans, G.: A parameterisation for the co-condensation of semi-volatile organics into multiple aerosol particle modes, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2017-123, in review, 2017.
Matthew Crooks et al.
Matthew Crooks et al.

Model code and software

dynamic_partitioning_param_GMD
M. Crooks
https://doi.org/10.5281/zenodo.801398
Matthew Crooks et al.

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Short summary
Clouds form when water condenses onto particles in the atmosphere and the size and chemical composition of these particles can have a large influence over how much water condenses and the subsequent formation of cloud. Additional gases exist in the atmosphere that can condense onto the aerosol particles and change their composition. We present a fast and efficient method of calculating the effect of atmospheric gases on the formation of cloud that can be used in climate and weather models.
Clouds form when water condenses onto particles in the atmosphere and the size and chemical...
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