MIT's Lab for Aviation and Environment has compiled data and published a paper showing that air pollution in the US (not to mention other countries where it is worse) causes 200,000 premature deaths per year.
Not surprisingly, the largest source of air pollution was fossil-fuel vehicles.
However, a surprising finding is that the second largest cause of premature deaths due to air pollution, is actually electric power plants, which are still largely coal-fired. In terms of particle emission causes of death, electric power plants are tied with vehicles, and are the number one source of sulfur dioxide, which is toxic. Other countries such as China and Russia are far worse.
So while electric vehicles are a great step forward in reducing air pollution and health impact, it is imperative that we move to cleaner sources of electricity generation as well. This is beyond the scope of transportation. Certainly, people in cities benefit from electric vehicles, but the people in the rural areas who live downwind of the power plants are being negatively impacted. The world's appetite for electricity (e.g. computers, servers) is only increasing.
BTW, although not mentioned in this study, MIT's Lab for Aviation and Environment has published many reports on air transportation effects on pollution, and have shown that air transportation -- particularly in Asia -- are a significant source of pollution. Interestingly, they have also shown that using alternative biofuels doesn't necessarily reduce greenhouse gas emissions.
Air transportation pollution in Asia and effect on health: