Patrick Collison rounds up a handful of different studies documenting the fact that air pollution makes people stupider:
Air pollution is a very big deal. Its adverse effects on numerous health outcomes and general mortality are widely documented. However, our understanding of its cognitivecosts is more recent and those costs are almost certainly still significantly under-emphasized. For example, cognitive effects are not mentioned in most EPA materials.
Patrick Collison
This may explain at least some of the tslaq dumdums.