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Nearly Nine of Ten Residents in Latin American Cities Are Exposed to Unsafe Levels of Nitrogen Dioxide (NO2) Pollution

Aerial view of Santiago de Chile under a layer of smog trapped between the hills

Philadelphia, PA, December 5, 2023


Over 200 million people in Latin American cities are exposed to nitrogen dioxide (NO2) pollution at levels that exceed World Health Organization (WHO) guidelines, according to a recent study led by researchers at Drexel University and published in The Lancet Planetary Health. Efforts to decrease reliance on fossil fuel-based transportation and increase neighborhood greenness may reduce exposure to NO2, safeguard health, and mitigate climate change.

Though not considered a greenhouse gas, NO2 interacts with other gasses in the atmosphere to contribute to the greenhouse effect and the formation of acid rain. At the ground level, NO2 contributes to ozone formation and is strongly associated with respiratory illness and diseases such as asthma, especially among children and older adults. Indoor NO2 pollution from gas stoves and other appliances also represents an important health risk.

Members of the Urban Health in Latin America (SALURBAL) project examined levels of outdoor NO2 in over 45,000 neighborhoods across 326 cities in Argentina, Brazil, Colombia, Costa Rica, Chile, Guatemala, Mexico, and Panama. Together, these cities are home to more than 230 million people. According to the study, over 85% of these residents live in neighborhoods with ambient annual NO2 levels that are above World Health Organization (WHO) guidelines.

By leveraging the unique data resource developed by the SALURBAL project, the research team was able to look for differences in NO2 exposure at the city, sub-city, and neighborhood levels, and to explore connections between NO2 concentrations and urban environment features.

Overall, variations in NO2 exposure were greatest across neighborhoods in the same city, rather than between different cities or countries.

“This is the first study to look at differences in NO2 exposure, not just across the region, but also within Latin American cities. This type of evidence helps us document disparities and can inform targeted actions to address these differences,” says Usama Bilal, PhD, MD, an assistant professor and co-director of the Urban Health Collaborative at Drexel University’s Dornsife School of Public Health, and a senior author on the study.

Cities with more vehicle congestion, larger population sizes, and higher population density tended to have higher levels of NO2. Across neighborhoods, closer proximity to city centers, and less greenspace predicted higher nitrogen dioxide concentrations. NO2 is produced by the burning of fossil fuels, and transportation represents an important source across Latin America and globally.

“In the context of international negotiations happening this month at COP28 in Dubai, these results further contribute to the health-based argument for reversing our dependence on fossil fuels,” says lead author Josiah Kephart, PhD, an assistant professor at Drexel University’s Dornsife School of Public Health. “Building and supporting cities where residents can walk, bike, and use public transit fueled by renewable energy will not only reduce our impacts on the climate but will also make our cities cleaner and healthier places to live.”

In addition to Kephart and Bilal,, the multi-country author team included Nelson Gouveia (University of São Paulo, Brazil), Daniel A Rodriguez (University of California at Berkeley, USA), Katherine Indvik (Drexel University, USA), Tania Alfaro (University of Chile, Chile), José Luis Texcalac (National Institute of Public Health, Mexico), J. Jaime Miranda (Cayetano Heredia University, Peru), and co-senior author Ana V. Diez-Roux (Drexel University, USA).

This research was made possible with support from the Wellcome Trust, the National Institutes of Health, and the Cotswold Foundation.

Read the full study: Ambient nitrogen dioxide in 47 187 neighbourhoods across 326 cities in eight Latin American countries: population exposures and associations with urban features

The Urban Health in Latin America (SALURBAL) project studies how urban policies and the environment affect the health of residents of Latin American cities. The results of this project serve as a reference to inform future policies and interventions to make cities healthier, more equitable and sustainable throughout the world. SALURBAL is funded by the Wellcome Trust. To learn more, visit SALURBAL and the SALURBAL Portal.

Contact: or Katy Indvik