Combustion-related nitrogen dioxide pollution appeared to significantly contribute to pediatric asthma incidence globally, particularly in urban areas, according to data published in The Lancet Planetary Health.

“Decades of research provide strong evidence that air pollution is bad for cardiovascular and respiratory health, but little information exists about the pollution levels and associated health consequences that cities around the world are experiencing,” Susan C. Anenberg, PhD, associate professor of environmental and occupational health and of global health at George Washington University, told Healio. “Because most cities globally lack air quality monitoring, our study is the first time that many cities have access to information about their air pollution levels and what they mean for children’s health.”

Anenberg and colleagues evaluated the long-term trends of annual average nitrogen dioxide (NO₂) concentrations and how they correlated with pediatric asthma burdens in 13,189 urban areas globally from 2000 to 2019.

The researchers utilized an existing annual average NO₂ concentration dataset for 2010 to 2012 from a land use regression model — based on 5,220 NO₂ monitors in 58 countries and land use variables — to model additional years using NO₂ column densities from satellite and reanalysis datasets. These concentrations were then applied in an epidemiologically derived concentration-response function with population and baseline asthma rates to estimate pediatric asthma incidence attributable to NO₂.

Anenberg and colleagues estimated that, in 2019, 1.85 million (95% uncertainty interval [UI], 0.93-2.8) new pediatric asthma cases were attributable to NO₂ globally, with two-thirds of those cases occurring in urban areas (1.22 million cases; 95% UI, 0.6-1.8).

“We found that over three-quarters of cities globally have nitrogen dioxide levels that exceed World Health Organization guidelines. As a result, we estimated that in 2019 about 16% of new cases of asthma among kids in urban areas were from breathing nitrogen dioxide. Globally, that’s down from about 20% in 2000, but the trend differs by world region,” Anenberg told Healio.

That 16% figure equated to 1.24 million pediatric asthma cases attributable to NO₂ out of 7.73 million total cases in 2019.

Urban attributable fractions rose between 2000 and 2019 in south Asia (+23%), sub-Saharan Africa (+11%) and north Africa and the Middle East (+5%). However, they decreased in “high-income” countries, including those in Australasia, high-income Asia Pacific, high-income North America, Southern Latin America and Western Europe (–41%); Latin America and the Caribbean (–16%); central Europe, eastern Europe and central Asia (–13%); and southeast Asia, east Asia and Oceania (–6%).

Researchers noted that the contribution of NO₂ concentrations, pediatric population size and asthma incidence rates to the change in NO₂-attributable pediatric asthma incidence varied regionally.

“Our study shows the importance of considering demographic changes over time for understanding air pollution health risks,” the researchers wrote. “Improved and more widely accessible information about disease rates, and capturing population distribution and movement, will enable more accurate and highly resolved air pollution health impact assessments.”