Urban air pollution, particularly from diesel cars but it does cover all vehicles is a real issue for health - which is why the most modern vehicles have the auto start/stop function.
No, the stop/start was mostly a propaganda and marketing exercise.
All modern cars are heavily reliant on the catalytic convertor (CAT) to reduce most of the pollutants. The CAT only works when it is up to full temperature which is around 426°C, the CAT is purely powered by the exhaust gases and actually increases the exhaust temperature.
As you can imagine, on switch off, at those sort of temperatures they cool down very fast to a level where they don't work, when you restart the car and drive off again, the CAT isn't working until it heats up again - you are now pumping out untreated exhaust pollution.
With the current regulations for new cars, emissions are absolutely minimal at idle with a warmed up engine and a heated up CAT, the cars are designed for optimal minimum emissions at idle, this process actually reduces the efficiency of the engine so more fuel is used than would be needed.
On a cold day with a cold car driving through a busy town, if stop/start was used there is a fair chance that the CAT would never get up to temperature and you are pumping out untreated exhaust pollution all the way.
Its a complicated subject.