An interesting report today in Data Center Knowledge that relates how Intel is finding server component corrosion beyond expected levels in equipment deployed in regions with very poor air quality - namely India and China.
Corrosion and dust accumulation were always the reasons cited for building data centers with no use of outside air for cooling. The Lawrence Berkeley National Lab did research to dispel this concern quite a few years back.
I still use a slide of their findings in my customer education deck, showing that the air outside of a facility in Fremont California was cleaner than any standard for computing equipment - though the only standard they could find was an old IBM spec. That spec was orders of magnitude higher than the requirements for healthy air from the EPA.
The real upshot of the research was that outside air, filtered to commercial office building standards, was perfectly suitable for supply to data centers.
Given the horrific reports of the air quality in China (I haven't seen much reporting on India), with PM 2.5 levels hundreds of times greater than US EPA standards, I would guess that data centers there would have significant filtering issues.
But I hope that this report does not raise the specter of declining equipment life from the use of outside air cooling back to life.
And for extreme conditions where air quality is so very poor, liquid immersion cooling begins to look like a very promising technology!