Children with asthma spend more time in the hospital when there is a greater amount of particulate matter (PM 2.5) and ozone (O₃), a colorless gas, in the air, according to a new study published in the Journal of Asthma.

The study, by researchers at the Children’s Hospital at Montefiore (CHAM) in Bronx, New York, comes soon after New York City was blanketed in wildfire smoke.

In this first-of-its-kind study in children, led by pediatric hospitalist Elissa B. Gross, DO, MPH, the investigators assessed medical records of more than 1,700 children, aged 2 to 18, admitted to CHAM between 2017 and 2019 and found that the mean length of stay increased up to 10% for every 10 micrograms of pollutants per cubic meter of air—equating to longer length of stay during times when air quality was poorer.

Asthma is a leading cause of pediatric hospitalizations in the United States. In the Bronx, asthma prevalence in children is 17%, compared to 5.8% nationally, according to a release from Montefiore Health System. There are many factors that impact the condition, including socioeconomic status, environmental triggers found in homes, such as mold and pests, and air pollution, which disproportionately affects Bronx residents due to the many surrounding highways. The Bronx also has more federal air quality violations than any other borough.

The analysis found that children with asthma, whose developing lungs are especially vulnerable to air pollutants, had longer hospitalizations when PM 2.5 in the air was high on the day of admission to the hospital and when O₃ was elevated the day prior to hospitalization.

“Our findings suggest that children with asthma may experience more severe exacerbations and remain hospitalized longer when they are exposed to a higher level of pollutants in the air,” says Gross, who is also associate professor of clinical pediatrics at Albert Einstein College of Medicine, in a release. “Hospitalizations are very disruptive to a child and their family, so it would be beneficial for everyone if there were more effective environmental policies that could help to prevent high levels of pollution so asthma exacerbations and chronic illness could be lessened for Bronx children.”