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Reductions in NO2 burden over north equatorial Africa from decline in biomass burning in spite of growing fossil fuel use, 2005 to 2017

Significance Socioeconomic development in low- and middle-income countries is thought to increase emissions of air pollutants, such as nitrogen dioxide (NO2). In Africa, fossil fuel use has nearly doubled since 2000, but vegetation fires—which cause substantial NO2 pollution—have declined, partly as a result of human activity. Satellite observations show that during the biomass burning season, NO2 concentrations in Africa’s northern fire region declined by 4.5% between 2005 and 2017, potentially benefitting hundreds of millions of people. Statistical modeling suggests that this decline is associated with declining vegetation fires. During the biomass burning season, higher levels of economic productivity are associated with lower NO2 concentrations, suggesting that socioeconomic development in this region is resulting in net improvements to air quality. Socioeconomic development in low- and middle-income countries has been accompanied by increased emissions of air pollutants, such as nitrogen oxides [NOx: nitrogen dioxide (NO2) + nitric oxide (NO)], which affect human health. In sub-Saharan Africa, fossil fuel combustion has nearly doubled since 2000. At the same time, landscape biomass burning—another important NOx source—has declined in north equatorial Africa, attributed to changes in climate and anthropogenic fire management. Here, we use satellite observations of tropospheric NO2 vertical column densities (VCDs) and burned area to identify NO2 trends and drivers over Africa. Across the northern ecosystems where biomass burning occurs—home to hundreds of millions of people—mean annual tropospheric NO2 VCDs decreased by 4.5% from 2005 through 2017 during the dry season of November through February. Reductions in burned area explained the majority of variation in NO2 VCDs, though changes in fossil fuel emissions also explained some variation. Over Africa’s biomass burning regions, raising mean GDP density (USD⋅km−2) above its lowest levels is associated with lower NO2 VCDs during the dry season, suggesting that economic development mitigates net NO2 emissions during these highly polluted months. In contrast to the traditional notion that socioeconomic development increases air pollutant concentrations in low- and middle-income nations, our results suggest that countries in Africa’s northern biomass-burning region are following a different pathway during the fire season, resulting in potential air quality benefits. However, these benefits may be lost with increasing fossil fuel use and are absent during the rainy season.