Given that recent Nature paper which claims that a lithium depletion could be responsible for Alzheimer's disease, is there any mechanism that could link increased air pollution to a reduction in lithium levels?

Some research suggests air pollution may disrupt blood-brain barrier integrity, potentially affecting mineral transport including lithium, while particulate matter can also bind to metal ions in the bloodstream altering their bioavailability.

Right now, most of the pollution–dementia work points more toward inflammation, oxidative stress, and vascular impacts rather than nutrient depletion

The two have been posited:

Lithium can be viewed an antioxidant – correctly or not?, I do not know.

Air pollution can be viewed as oxidative stress.

It’s interesting to search Google Scholar for “lithium antioxidant”.

Exposure to another similar metal could in theory displace lithium in biological processes.