Hi Ranger.
I help look after a huge regional distribution Centre.
Which has had dust build up issues from day one (2011).

With various parties trying to fathom out what was causing the issue.

Basically there are 3 major constituents to this green claggy dust.
Which can with the addition of moisture created a hard crust across the surface of the coolers.
It's no new phenomenon, ask any old school Cold store engineer.

Part 1. Cement Dust from the Chill or Cold Store Warehouse Floor.
Usually caused by the vehicular traffic within the store.
The new practise of H&S where a pallet is dragged across the floor rather than with Ground Clearance.
Causes the production of Cement dust and Wood fibres.(Also see Part 2.)

Part 2. Wood fibre produced as the pine pallets are dragged around the store.


Part 3. Blue paint ( Industry standard Chep pallets are painted Blue.)
This usually results in a blue greed dust.

Add freezer coolers which are of a standard design which relied Historically on the flushing action of a deep defrost across the fins. with large drains to boot!
That actually nowadays have anything like the volume of frost upon them prior to defrost.
Especially where Munters units are on the loading bay and pre chamber entrances.

This freezer store is so efficient (Once set up correctly) that I would defrost any of the 6 coolers. every other day if the controlling software let me.
Because it doesn't need any more frequent defrosts the downside is the cooler surfaces don't get flushed.
With anything like the volume of water that we were used to.
So efficiency is to the detriment of cleanliness.

Simply put we rotate the coolers and reduce the defrosts. but at some point you have to clean them.
The customer hates having to have them cleaned, but the efficiency gets progressively worse if you don't.

The chill store (2.0c average) has similar issues but are fitted with standard paper Filters.
Which capture huge amounts of dust and can last as little as 8 weeks 240 at a time.
Is not cheap!

Plastic pallets may be the option of the future but dust and pallet particles would still be an Issue.

Raising your store control temperature slightly can help by slightly raising the humidity slightly also.

Which itself can help control the airborne dust.

It not a new problem my friend!
Historically I have also known Diesel fumes and brake dust particles.
which are carried into the chamber be part of the equation!
Good luck all the same.
Grizzly