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An existing equilibrium partitioning model for calculating the equilibrium gas/particle concentrations of multiple semi-volatile organics within a bulk aerosol is extended to allow for multiple core aerosol modes of different sizes and chemical compositions. In the bulk aerosol problem the partitioning coefficient determines the fraction of the tot...
Contexts in source publication
Context 1
... most significant change to the theory for multple modes is that the equations must explicitly take into account that a single molecule of an organic cannot condense onto more than one core mode. Consider the 10 organic molecules and 2 core particles shown in blue and green respectively in Figure 1. Suppose the subset highlighted in pink are known to condense onto the left core particle; ...
Context 2
... parcel model is run with the parameters given in Table 5 together with the material properties from Table 3 and the second mode is given an initial period of 1500 seconds of simulation time 445 before the smaller mode is added. The subsequent time evolution of the condensed concentrations are shown by the solid lines in Figure 12 for a relative humidity of 0% and 90%. Bulk equilibrium is reached by about 1000 seconds and the parcel model converges on a value which is in good agreement with the partitioning theory shown by the dashed lines. ...
Context 3
... equilibrium calculated using the parcel model is further compared against the partitioning 460 theory in Figure 14 Geosci. Model Dev. ...
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Citations
... This parameterisation was later extended to include multiple non-volatile aerosol modes (Crooks and Connolly, 2017). Petters and Kreidenweis (2007) present the hygroscopicity, κ, as a method of characterising CCN 80 activity through relating dry diameter and supersaturation into a single parameter. ...
We present a novel method of exploring the effect of uncertainties in aerosol properties on cloud droplet number using existing cloud droplet activation parameterisations. Aerosol properties of a single involatile particle mode are randomly sampled within an uncertainty range and resulting maximum supersaturations and critical diameters calculated using the cloud droplet activation scheme. Hygroscopicity parameters are subsequently derived and the values of the mean and uncertainty are found to be comparable to experimental observations. A recently proposed cloud droplet activation scheme that includes the effects of co-condensation of semi-volatile organic compounds onto a single lognormal mode of involatile particles is also considered. In addition to the uncertainties associated with the involatile particles, concentrations, volatility distributions and chemical composition of the semi-volatile organic compounds are randomly sampled and hygroscopicity parameters are derived using the cloud droplet activation scheme. The inclusion of semi-volatile organic compounds is found to have a significant effect on the hygroscopicity and contributes a large uncertainty. For non-volatile particles that are effective cloud condensation nuclei, the co-condensation of semi-volatile organic compounds reduces their actual hygroscopicity by approximately 25 %. A new concept of an effective hygroscopicity parameter is introduced that can computationally efficiently simulate the effect of semi-volatile organic compounds on cloud droplet number concentration without direct modelling of the organic compounds. These effective hygroscopicities can be as much as a factor of two higher than those of the non-volatile particles onto which the volatile organic compounds condense.
