Accra — Harmful emissions of nitrogen dioxide (NO2) were reduced in 13 African countries in recent years, bucking the trend of increasing air pollution, as rural to urban migration led to a decline in agricultural burning, a study suggests.

Researchers say that Africa has about 70 per cent of burned areas globally, with the practice of bush burning — setting fires during dry seasons to clear land — particularly common in north equatorial Africa. The region is home to over 275 million people and spans 15 countries including Cote d’Ivoire, Ghana, Senegal, South Sudan and Uganda.

The study published in the Proceedings of the National Academy of Sciences last week (16 February) assessed air pollution seasonal fires and population growth in the grassland region of north equatorial Africa during November to February from 2005 to 2017.

Researchers used satellite data and imagery to measure the amounts of nitrogen dioxide (NO2) gas as a measure of air pollution. They also used satellite imagery to measure burned areas.

“Our study finds that there is a decline in NO2 of 4.5 per cent in that region during that time of year,” said Jonathan Hickman, lead author of the study and a researcher at NASA’s Goddard Institute for Space Studies at the US-based Columbia University.

“That would suggest that there are likely also some decrease[d] air pollution-related health problems in that region during the dry season, but we do not have any specific evidence for this.”

A report by UNICEF indicates that air pollution is a growing challenge in Africa, with deaths in Africa from outdoor air pollution rising from 164,000 in 1990 to 258,000 in 2017.

Biomass burning contributes greatly to the release into the atmosphere of NO2, a harmful pollutant linked to health issues such as lung and respiratory diseases.

According to the study, economic and demographic data showed that decreases in NO2 were linked to areas where populations and economic activities had increased, leading the researchers to suggest that rural to urban migration might have contributed to the decline in NO2.