When The Shard catches the morning sun at 7am, the view from Stephanie McDonald’s sixth-floor Clapham apartment is breath-taking. The air outside is not. Below her £950,000 property, vehicles bustle down the A24 during rush hour, belching out nitrogen dioxide (NO2) and other pollutants. On clear days, she can see the smog hanging moodily over the City. Tiny particulates, according to official figures from Clean Air in London, an air-quality pressure group, claim up to 9,500 lives a year in the capital and as many as 79 per cent of Londoners say they want to be told when pollution is high, according to a major air consultation launched by the London Mayor, Sadiq Khan, in July. Still, it doesn’t worry McDonald...