We show that the limit of the enhancement of coagulation scavenging of charged particles is 2, that is, doubled compared to the neutral case.
Because the particle survival probability decreases exponentially as the coagulation sink increases, everything else being equal, the doubling of the coagulation sink can amount to a dramatic drop in survival probability – squaring the survival probability,

There are many situations in atmospheric phenomena where we care about total particle number, and especially total particle number above some critical size.
An example is cloud activation, where the total number of cloud condensation nuclei is often estimated to be the total number of particles with diameters

The particle survival probability decreases exponentially as the coagulation sink increases

Small charged particles are intrinsically out of equilibrium

For particles larger than roughly 10 nm, the dominant mechanism for gaining and losing charge (in the atmosphere) is diffusion charging, either from primary ions or other sub-10 nm particles if these represent a large fraction of extremely small and mobile ions.
For

We present a simple derivation of this limiting behavior, where the presence of charge leads to the doubling of coagulation losses.
For particles with

Because all particles are at most singly charged in this limiting derivation, this applies to bigger particles comprising the coagulation sink,

Accordingly, we define the diffusion charging rates and set them in equilibrium in Eq. (

Ion–particle flux attachment coefficient

To illustrate this derived limit further, we use primary ions as a limit for the smallest particles.
We compute the limiting behavior from available data,
assuming that the coagulation between smaller particles and bigger particles is the same as the coagulation of primary ions with bigger particles.
In this case, we study the coagulation sink ratio, defined by

We assume the smallest particles (at

In Fig.

The ratio of the coagulation sink of charged (

Coagulation sink ratios shown in Fig.

For convenience, we present two parameterizations that capture this limiting behavior in Fig.

We have shown that the limit of the enhancement of coagulation scavenging of charged particles is 2 – double that of neutrals.
Particle survival probabilities decrease exponentially as the coagulation sink increases

No data sets were used in this article.

NMD conceived of the research question herein; NGAM and NMD conducted the research, interpreted the results, and wrote the paper together.

The authors declare that they have no conflict of interest.

We thank the editor, reviewers, and editorial staff for their help in finalizing this paper.

This research has been partly supported by the National Science Foundation (NSF) (grant nos. AGS1740665 and AGS1801897).

This paper was edited by Veli-Matti Kerminen and reviewed by two anonymous referees.