Thanks for your wonderful work.

I conversed with Marvin some time ago. He suspects that coal fly ash and additives to keep it suspended may be added to the fuel at a stage after it is produced and before it is delivered to the airports.

I looked at numerous papers supporting his thesis that fly ash particles have a huge weighting in cirrus cloud formation.

Of central importance is this one that states that fly ash obtained from cirrus clouds is very difficult to distinguish from mineral dust and tends to be coupled with it by scientists. They found that 7% of the cirrus clouds they sampled were formed on anthropogenic fly ash.

Ice nucleation by combustion ash particles at conditions relevant to mixed-phase clouds

The question I have is how is coal fly ash differentiated from jet fuel combustion ash?
Jet fuel exhaust emits about 0.01% ash, the US EPA standard being 0.02% ash. About 0.045 kg of ash is produced for every 450 kg of fuel burned. This works out as around 254,276 x 1012 submicron particles emitted per metre of flight.

They seem to have similar properties in being the metallic residue left behind when the carbonaceous component has been combusted away.

I go into more detail on my blog:

A Study in Infra-Red part 9: The Riddle at the Heart of Ice
https://bakerstreetrising.home.blog/2019/04/29/a-study-in-infra-red-part-9/