'City Flocks' sends pigeons with sensors on their backs into the sky with the aim of recording more accurate pollution forecasts.
Experts warn Nigeria's health system is heading for a crisis if pollution is not tackled.
Watch and listen to more stories from around the globe on BBC World Service radio
US study reveals how much trees help tackle urban air pollution
Introducing the So I Can Breathe season on the BBC - a look at possible solutions to air pollution.