This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: An air pollution monitoring network has provided one of the most detailed long-term views yet of the role of black carbon, or soot produced by fires, diesel vehicles and other combustion sources, in Ethiopia's capital, Addis Ababa. The detailed measurements show how pollution changes by time of day and season, including increases associated with rush-hour traffic and holiday celebrations.
The findings are relevant to cities around the world, including in the United States. In a paper published in ES&T: Air, scientists analyzed data collected throughout Addis Ababa between 2022 and 2025 from 10 air-quality monitoring sites deployed by NASA's Multi-Angle Imager for Aerosols (MAIA) project. The research comes as Ethiopia is taking steps aimed at improving air quality.
In 2024, the country became the first in the world to ban the import of internal combustion engine vehicles, while cities have been adding bike lanes and electric vehicle infrastructure. The MAIA project's measurements provide researchers with a baseline for understanding how air quality changes over time as Addis Ababa continues to grow and evolve. The study focuses on particulate matter that is 2.5 micrometers or less in diameter, also known as PM2.5.
The 2025 State of Global Air Report, cited in the paper, estimates that exposure to PM2.5 is associated with approximately 4.9 million deaths globally each year. Among the many kinds of PM2.5, black carbon has been studied for its potential effects on human health. The paper found that Addis Ababa's three-year average PM2.5 concentration was 30 micrograms per cubic meter, which is more than three times the level of the U.S.
Environmental Protection Agency's health-based annual PM2.5 standard. The new paper cites data from MAIA's ground sensors indicating that average black carbon levels in Addis Ababa were approximately four to nine times higher than those measured in the three U.S. metropolitan areas the mission is monitoring. "To our knowledge, this is the first long-term, multisite study of continuous PM2.5 and black carbon measurements in Ethiopia," said Sina Hasheminassab, a co-author of the paper and MAIA's deputy principal investigator at NASA's Jet Propulsion Laboratory in Southern California.
"Many rapidly growing cities have limited long-term monitoring, so these measurements provide an important baseline for understanding how pollution changes across space and time." The composition and sources of PM2.5 can differ substantially between cities, depending on their local geography, traffic, industries and more. Desert cities, for example, may have more dust, while those near coal-fired power plants may have higher concentrations of sulfate. Long-term surface measurements remain limited in many parts of the world.
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