<p>Socio-economic development in low and middle-income countries has been accompanied by increased emissions of air pollutants such as nitrogen oxides (NO<sub>x</sub>: nitrogen dioxide (NO<sub>2</sub>) + nitric oxide (NO)), which affect human health.&#160; In sub-Saharan Africa, fossil fuel combustion has nearly doubled since 2000.&#160; At the same time, biomass burning&#8212;another important NO<sub>x</sub> source&#8212;has declined in Africa&#8217;s northern biomass burning region, attributed to changes in climate and anthropogenic fire management associated with agricultural development. Here we use satellite observations of tropospheric NO<sub>2</sub> vertical column densities (VCDs) and burned area to identify NO<sub>2</sub> trends and drivers over Africa. Across the northern ecosystems where biomass burning occurs&#8212;home to over 350 million people&#8212;mean annual tropospheric NO<sub>2 </sub>VCDs decreased by 4.5% from 2005 through 2017 during the biomass burning season of November through February. Reductions in burned area explained the majority of these change in NO<sub>2</sub> VCDs, but there were also weaker relationships between changes in NO<sub>2</sub> VCDs and fossil fuel emissions over parts of West Africa, which were stronger during rainy season. Over Africa&#8217;s biomass burning regions, NO<sub>2</sub> VCDs tended to decrease with increasing population density up to a threshold of approximately 180 people per km<sup>2</sup>, suggesting that anthropogenic activity causes a net reduction in NO<sub>2</sub> emissions&#160;across roughly 90% of the continent&#8217;s biomass burning regions. In contrast to the widely-held perception that socio-economic development worsens air quality in low and middle-income nations, our results suggest that countries in Africa&#8217;s northern biomass burning region are following a different pathway, resulting in regional air quality benefits. However, these benefits may be lost with increasing fossil fuel use.</p>
