Question: Can we call the number of particles per unit volume a "number density"?

[jeff-cohere]

Currently we store the total number of particles in a mode in a quantity that we call the "number concentration". In regular physics, a concentration refers to a quantity that describes the ratio of something to something else, usually in moles or mass or something. A quantity specified per unit volume is usually referred to as a "density" (like mass density, energy density, number density, charge density, and so on).

Can we switch to the terminology "number density" for our modal per-volume particle counts? It would be much less confusing for me. If the atmospheric physics community as a whole uses "number concentration" for number per unit volume, that's fine, but if both terms are used in that field, I very much prefer "number density", because it can't be confused with other kinds of concentrations.

@huiwanpnnl @singhbalwinder @pbosler

[huiwanpnnl]

Perhaps we are facing a difference between the language used in physics and the language used in chemistry? See this page.

Several times in the past we have mentioned the idea of creating cheatsheets (for different purposes). Perhaps we should list all the different densities, "concentrations", mixing ratios, and related quantities in one document and then see if we can find a way to unambiguously name all of them?

[jeff-cohere]

Indeed. Thanks for the pointer, Hui. It seems like the aerosol literature is mostly written in the language of chemistry (which makes sense, given its outsized influence). I can live with "number concentration" in that case.

[huiwanpnnl]

I must admit I also prefer "number density" :-)