I read somewhere that 50% of particulate pollution comes from brake discs/pads and tyres, meaning that electric cars will still cause air pollution. But hey, half as bad is twice as good.

The existence of regenerative breaking means that the amount of pollution from the little friction breaking still necessary should be much less.

Regenerative breaking doesn't wear pads, so only emergency breaking would count towards that 50%.

> black soot in my nose in London.

That's probably dust from the London Underground, which is mostly iron (from the rails and wheels), brake dust (ceramic) and dead skin.