This study introduces AerSett v1.0 (AERosol SETTling version 1.0), a model giving the settling speed of big spherical aerosols in the atmosphere without going through an iterative equation resolution. We prove that, for all spherical atmospheric aerosols with diameter

One of the main purposes of chemistry–transport models (CTMs) is to simulate the aerosol concentration in the atmosphere as accurately as possible. The settling velocity of aerosols is a key driver of their dry removal from the atmosphere

However, dust particles exist in the atmosphere with different sizes from

The settling speed of giant particles deviates substantially from the Stokes law, an effect that can be taken into account using mathematical formulations known as large-particle drag corrections. Usually, these large-particle drag corrections are performed by using empirical formulations of the drag coefficient

Since it has been highlighted by

In Sect.

We will follow the notations of

In the case of spherical particles and for extremely small Reynolds numbers,

While Eq. (

Equations (

Solving Eq. (

To slightly generalize matters, let us rewrite Eq. (

Injecting Eq. (

Now, we proceed supposing that the expression of

Figure

So far, for the sake of simplicity, we have assumed that continuum fluid mechanics apply to our falling particles. As explained in, e.g.,

To summarize the previous development, the method we have designed to calculate

Calculate

Calculate

Calculate

Ratio

Apart from its simplicity, another possible advantage of the straightforward evaluation of

A Fortran code has been designed to estimate the calculation cost for these three methods (Fig.

To optimize calculation speed, we have observed that for

Figure

Execution time in nanoseconds (ns) for the three numerical methods described in Sect.

As a conclusion, we have found that the following method is suitable to evaluate the settling speed of spherical aerosol particles in the atmosphere,

Equations (

Equation (

To go further in understanding the settling speed of giant dust particles and be able to represent them in chemistry–transport models, it is necessary to extend simple models such as AerSett to the case of non-spherical particles, and give simple and straightforward estimates of the drag correction factor

All the simulations and figures have been performed with Python scripts and Fortran code available according to the GNU General Public License v3.0 at

All the available versions of the AerSett Fortran module are available according to the GNU General Public License v3.0 from

No data sets were used in this article.

All authors have contributed to the article by stirring the ideas, writing and correcting the paper, and providing bibliographical reference. SM has developed the Python scripts used to produce the plots.

The contact author has declared that none of the authors has any competing interests.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

The authors acknowledge the developers of the Python modules “Thermo”

This paper was edited by Samuel Remy and reviewed by two anonymous referees.