I would think the water that evaporates to the atmosphere is clean water & the pollutants are left behind in the land & oceans. Clean water can absorb pollutants in the atmosphere on the way back down though.
So depending on the pollutant and it’s weight compared to water, it may be lost as it rises to the atmosphere and dropped to the earth, so it is not cleaned. The aspect is that increased carbon dioxide in the atmosphere, results in acidic rain or carbonic rain. This acidic rain is known to leach soil of nutrients and damage old buildings and statues. Once most chemical pollutants are in our environment, they are very difficult to remove and require biological processes (happening over long time periods) to breakdown them down into less harmful components.