Two researchers from the public health school found that millions of asthma-related visits to the emergency room each year are caused by air pollution.

In a study published last week by a group of researchers representing 14 institutions, two researchers from the Milken Institute School of Public Health found that air pollution caused by two chemicals led to roughly 14 to 33 million emergency room visits globally in 2015. Researchers involved with the study, who pursued the subject using a grant from NASA’s Health and Air Quality Applied Science Team, said the results can be used to combat air pollution in the hopes of reducing asthma and improving global health.

Susan Anenberg, an associate professor of environmental and occupational health and the head researcher on the study, said the link to air pollution and emergency visits has never been studied before on a global scale and will help clinicians and public health practitioners trying to reduce the burden of asthma.

“Trying to understand or more comprehensively account for the health impact of air pollution would be able to help decision-makers more efficiently improve public health,” she said.

Anenberg said the research has been ongoing since about 2016 and was based on an annual report entitled “The Global Burden of Disease,” which estimates the impact of risk factors – like air pollution – on public health issues.

“One that was particularly interesting to us was asthma because that’s a disease that I think is tangible to lay audiences, and if you were to ask someone who is not in the air pollution field which diseases are affected by air pollution, asthma is one of the first things they would say,” Anenberg said.

Asthma is the most prevalent respiratory disease worldwide and affected 358 million people in 2015, according to the study.

She said the team of researchers used a literature review approach and reviewed analyses and studies that focused on the concentrations of pollutants in the air – like ozone, particulates and nitrogen dioxide – around the world in countries like China and India.

“One thing that did stand out to me was that it was not the case that one pollutant dominated over the others, and it appears that most pollutants are going to be necessary to try to bring down the negative impact of air pollution,” she said.

Anenberg said the most challenging part of the research was trying to understand the influence nitrogen dioxide has on asthma since it is “short-lived” in the atmosphere and varies in different areas, like near roadways.

“We used a combination of satellite remote sensing and atmospheric modeling to get at that, but our methods were still pretty limited,” she said. “We’re now following up this study with another study using a different technique to try to get at nitrogen dioxide exposures around the world near roadway gradients.”

Veronica Tinney, a doctoral student at Milken who contributed to the study, did not return multiple requests for comment.

Daven Henze, a principal investigator on the study and an associate professor at the University of Colorado Boulder, said he was involved in estimating the air pollution concentration levels throughout the world.

“I think that the overall magnitude of the impact of air pollution on asthma was pretty surprising,” he said.

He said the percentage of polluted air was more than 10 percent in some areas, which contributes to the number of visits to the emergency room – a figure he said “was pretty remarkable.”

“I think we knew going into this that there was definitely a connection between air pollution and asthma, and people have studied that regionally, but the fact that it played out to be such a large percentage when you look at the global budget, I think that was surprising,” he added.

He said the researchers examined emergency room visits for asthma in about 54 countries and looked at global air pollution levels, which come from satellites, to help researchers estimate levels of air pollution concentration.

Henze added that countries like China had higher concentrations of air pollution because of a large population and few restrictions on factory emissions.

“I think what’s novel about that is it then brings this issue to sort of the forefront of global health issues,” he said. “You can start to put this number in comparison to other factors that drive policy or resources in the global health community and think about the issues, beyond you know domestic or regional problems, but something that is impacting people all over the world.”

Madeleine Deisen and Cristina Cestone contributed reporting.