While on this non work rabbit hole, I found that a ballpark measure of the density of the zodiacal dust as observed by the Mariners is ONE PARTICLE PER CUBIC KILOMETER. Capitalized because of its wonderful simplicity.

https://www.sciencedirect.com/science/chapter/edited-volume/abs/pii/B9780080128351500519

Yeah, the abstract says "Mariner II and the Mariner IV data seems to indicate that the particle number density varies from 10−16 to 10−14 particle per cm3 and the spatial density ranges from 10−26 to 10−24 gram per cm3 between 0.72 A.U. and 1.56 A.U."

So if you take the middle of their range of particles per cm^3, which is 10e-15 per cm^3, and bring it to unity, because mental model sanity, because a part of a particle is one particle & parts of particles DON'T EXIST, then you come out with the amazingly easy to remember 1 particle per km^3. Why wouldn't you put that in your abstract?