Numerous well done studies exist about the impacts of EV, how many years before their real benefit might be realized and so on and if you search around, you will find them.
For example... here's a recent article from Proceedings of the National Academy of Sciences done by a group at UMinn Engineering School and National Renewable Energy Lab in Colorado:
http://www.pnas.org/content/111/52/18490.full.pdf
These figures are particularly telling:
http://www.pnas.org/content/111/52/18490.figures-only
The grid average as of 2014 show EV twice as damaging to air quality as gasoline or diesel. The units are given as both "Mortalities per year" and "Externality damages per one gallon gas equivalent." As the grid is now, EV is worse than conventional gasoline. Diesel is slightly better than conventional gasoline.
Yes, the same graph show that EV can be much much better than diesel or gasoline when charged from wind, dynamic water or solar. I would never consider EV where I live (I have solar hot water but buy power from the utility otherwise). If I moved someplace where I could put up my own PV or wind and my driving matched the right profile, lots of <40 miles per day, thought I could get 200k miles per battery, I would consider EV. Otherwise, the grid support for EV still looks 15-20 years out. I live in Berkeley, CA. Most of my around town is by bicycle. When I get in the car, I'm either hauling something heavy or driving 500+ miles that day. Diesel remains my choice for those tasks.