That’s a very interesting observation.
There is an entire chapter on this in Comets II (edited by Festou, Keller and Weaver) which describes the generation and distribution of species in the coma (pp 425 onwards). It was published in 2004 before much of the recent space-based observations of comets but it is an excellent reference book if you can get hold of a copy. I can see some second-hand around £60 online. The book is so massive that it is in imminent danger of collapsing under its own gravity. A more recent book, “An introduction to comets” by Nicolas Thomas is post-Rosetta and also covers this.