When Waziri Abubakar ran the Lagos Marathon this year, he was determined to beat his personal best of 4hr 13min. But he also had another aim: to measure air quality along the route. With 50,000 people running, it was the perfect opportunity for Abubakar to raise awareness of Cityzens for Clean Air, a campaign he had joined seven months earlier.

Wearing sensors and using a smartphone app, Abubakar measured the most harmful pollutant: the fine particles in the air known as PM2.5, less than 2.5 microns wide.. In 2019, Nigeria’s annual average PM2.5 figure was 14 times greater than the World Health Organization’s recommended levels.