Toxic smog has been a part of big city life since the Industrial Revolution: a pea-soup blanket of harmful particulates that can be so thick that seeing and breathing is difficult. Yet in many cities in the rich world that dirty pall has been banished as car engines have got cleaner and factories have moved away. (Poorer cities are not yet so lucky.)
Some people believe that the shift to electric cars could reverse some of that progress: that heavier cars and the particulates they produce by friction mean we could sacrifice cleaner air on the altar of zero carbon emissions.
