I went to an Alzheimer's Conference recently and there was an hour-long talk about air pollution and dementia.
1) The title of this article is bad. In epidemiologic terms, you shouldn't combine the words "seem" and "cause". Seem is about perception, is about possibility, whereas any science writer or epi researcher worth their salt is NOT going to use the term "cause" lightly. There may be an association, a correlation, a linkage even, but cause? No no, dementia is a very broad disease with many potential causes, and likely you will never establish a singular cause for that disease.
2) Regarding the talk I attended itself, there is a wildly broad definition of air pollution out there. Are you talking about ozone, NOx, or particulate matter, and what SIZE of particulate matter? How do you measure lifetime exposure or recent exposure for those moving, and for the dynamic process that is air quality? Then, how do you control for community and cultural based effects of living in certain areas - maybe those with other risk factors are also those forced by poverty/etc. to live in the polluted areas.
Summarily, IMHO, air pollution is a contributing factor to dementia, but alone I doubt it'd be sufficient without age-related degeneration, unhealthy diet, lack of exercise, stress, underlying genetics/alleles/mutations, etc. There are probably around 10-20 important factors of which air pollution is one.
As a society, let's ditch ICE vehicles, let's ditch coal and dirty industrial practices, both for our planet and for our own health.
What can you do now? Stop idling your car, use your brakes as little as possible (i.e. drive efficiently, don't speed up just to have to brake soon), don't go out in hot summer weather, support renewable energy, oppose coal/dirty diesel/inefficient fossil fuel use, and generally vote for politicians who agree with the above and don't take dirty fossil money.