Grey plaque scheme highlights NO2 pollution in London

London’s Choking initiative aims to draw attention to areas where nitrogen dioxide pollution threatens public healthThey take their inspiration from the well-known signs linking people from the past with the buildings they once inhabited, but the symbols now appearing across London are to highlight a different connection.In the past week, grey plaques – direct copies of the English Heritage blue plaques identifying the homes of the dead and famous – have been put up on building