Nino Tronchetti Provera has vivid childhood memories of the unpleasant effects of air pollution. “I was biking in Milan as a kid and my shirt was black after five minutes,” he says, recalling the haze of the city’s refineries and steel plants belching fumes into the air of northern Italy. These days Mr Tronchetti Provera is managing partner of Ambienta, the private equity firm he founded, which invests in companies that tackle waste and pollution. Private equity may not be famed for its ethical credentials.