Tab::Cluster formation (nucleation)

ACDC

ACDC has much more features than what are used in ARCA, and any user who wants to properly study cluster formation, should familiarize oneself to ACDC. Explaining the finesses of ACDC here is outside the scope of this manual, and the curious reader is referred to ACDC repository, where the manual and full model source can be found.

Print clusters

This will print the concentrations of all the clusters in the ACDC system.

Run ACDC to steady state

This option should only be used if the model is used so that any rate calculated by ACDC should be independent of the history. It should not be used in a dynamic situation, such as simulation of atmospheric or chamber conditions. It can be used for example if you want to create data which shows formation rate as a function of some independent variable, for example temperature or sulfuric acid concentration.

Edit ACDC systems (WARNING, only for experienced ACDC users)

Here you can open the files that define the sulfuric acid - ammonia and sulfuric acid - dma systems. To apply any changes the following procedure is needed:

You need to run the ACDC perl program which are found in the src/ACDC/<system> directories (requires perl in your system, usually already available in Linux):

- For DMA, navigate to "src/ACDC/ACDC_module_2016_09_23" and (in terminal) type ./run_perl.sh

- For Ammonia, navigate to "src/ACDC//ACDC_module_ions_2018_08_3" and (in terminal) type ./run_perl.sh

-> recompile ARCA

How do these files affect the formation of clusters?

Changing the cluster input files corresponds to using different thermochemical data for cluster evaporation, and / or a different set of cluster compositions and sizes included in the cluster formation simulation. This affects the quantitative formation rates for a given cluster formation chemistry.

By default, the thermochemistry and cluster set correspond to previously published RICC2//B3LYP data (see Olenius et al., 2013). This data set performs reasonably well compared to laboratory experiments (e.g. see here), but cluster evaporation tends to be underpredicted and thus the formation rates can be considered upper-limit estimates.

More information regarding these cluster systems:

https://aip.scitation.org/doi/10.1063/1.4819024

https://www.nature.com/articles/nature12663

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JD023908

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JD026501

https://pubs.acs.org/doi/10.1021/acs.jpclett.0c01045

Parametric cluster formation

This option uses the method described in Roldin et al. (2019). Nat. Commun. where the formation rate of 1.5 nm particles due to clustering of sulfuric acid and (some unknown) organic molecules is defined as:

J_1.5 = k * [ORG]*[H2SO4],

where

k = 5e-13*exp(-dH/Rg * (1/T[K] - 1/298[K]))

and dH = dG - dS*T

dG = -15100 [cal/mol], dS = 61.1 [cal/mol/K] are based on Elm et al. (2017), J. Phys. Chem.

The nucleating organic vapour is defined in the file nucl_homs, which you can edit by pressing "Edit list of vapours that nucleate". The vapours are summed up and generally should be such that they are found from the chemistry.