Anthony Steed wanted to know how polluted the air was on his daily cycle commute. So in April 2005 he packed a backpack with a carbon monoxide sensor, GPS receiver and a data recorder, and set off to his office in the computer science department at University College London.
After wearing the backpack for two months along the same route he and his colleague Richard Milton analysed the data. They found that just as Steed passed over a particular railway bridge, the sensor registered a large spike in the level of carbon monoxide.
Like most cities, London has only a…
