A few comments and observations.
I'm not aware of any areas on the globe that are immune to pollution.
In the south of the UK, we ( most years ), get plagued with sand from the sahara.
We have also suffered from European birch pollen. No border controls are likely to stop that one
The more usual occurence, being acid rain.
Acid rain is most commonly associated with nitrogen or sulphur. Apart fom industrial causes, the more recent problems of volcanic activity and worldwide wildfires will exacerbate this issue.
The corrosion on the surface conditioning mesh.
Firstly, there is no such material as "stainless" steel. The phrase was originally concocted as a marketing ploy, a more accurate description (and one used in some metal reference books), is corrosion resistant steels, with accent on the word resistant.
The mesh used will be either an austenitic or ferritic "stainless" steel. Probably the latter. In either case, they will both show evidence of corrosion given the right conditions.
An issue that I do believe is Ecowitt's responsibility is the concentration of corrosion around the silicone used to bond the mesh to the plastic.
This strongly suggests that an acidic cure silicone has been used, where a neutral cure silicone would have been a better choice.
My own WS80 exhibits some signs of corrosion, but I would expect this to remain superficial, and not detrimental to the performance.
Cracks in the solar panel.
It's always diificult to be sure from a photograph, so I will reference both my original and its replacement.
Both units show similar marks, and indeed, I inspected them closely when they were new.
In the case of my units, I believe them to be injection moulding flow lines, and should not be detrimental.
Just in case this is something you may be considering.
I would not recommend coating the mesh with any form of protection.
The mesh appears to have been grit (dry or vapour) blasted to affect a particular surface finish.
Any change could alter its effectiveness.