How long does it take air to circle the world? I live in New York and I am investing in a carbon offset program in Korea to decommission a coal electricity generation plant.

Will I ever breathe the cleaner air as a result of that project? And how long with that air to get here (and back around)?
It takes about 2 weeks for a mass of air to circle the globe along its latitude from West to east. I used to work for a French climate research lab in the 70s, and was based on Crozet island (South Indian Ocean) . At the time I was carrying atmospheric radioactivity measurements, and the French army was carrying nuclear test above ground in the pacific, I could see the radioactive cloud passing above me about 10 days later and then again about every second week after that and about completely disappeared after 6 months.
In the case you raise, you will benefit from cleaner air about one week after the decommissioning