Discharge day in the neonatal intensive care unit, or NICU, should feel like a finish line. After weeks or months of monitors, alarms, oxygen, feeding tubes, blood tests and waiting, a family can finally take their baby home.
As a neonatologist, I know how much work it takes to get that baby there. Their lungs have grown stronger. Their feeding has improved. Their medications have been adjusted and readjusted. The car seat test has been passed.
But every time we prepare to discharge a preterm infant, I find myself thinking about something that is not listed in the NICU discharge summary: What is the air like in the home and neighborhood where this child lives?
That question has animated my clinical and research life. Before I was a neonatologist, I worked in a toxicology lab studying fine particulate matter, or PM2.5. These are tiny particles produced by sources such as vehicle exhaust, power plants and industrial emissions. They are small enough to be inhaled deep into the lungs and may enter the bloodstream. In the lab, we studied how early-life exposure to polluted air could affect the developing heart and lungs.
Years later, caring for preterm infants in Philadelphia, I am confronted by the same question. Not in a dish or an animal model, but in the lives of my patients – whose lungs are still developing when they leave the hospital – and their parents.
Preterm infants face double exposure
Before my patients are born, their pregnant parent is already breathing the air in the place they call home, whether that’s in Philadelphia, Delaware County or beyond. When a pregnant parent breathes polluted air, it may increase the risk of preterm birth, making it more likely I’ll see that baby in the NICU.
But delivery does not end the exposure. The same air pollution may still be there when the infant comes home. The difference is that now, alongside their parent, a preterm infant with developing lungs is breathing it too.
That means some infants may face a double exposure: first before birth, then again after discharge.
Small pollution differences can have big impacts
In Philadelphia and other large cities, the distribution of dirty air – and therefore the likelihood of facing this double exposure – reflects how American cities have been built. Highways, industrial sites and traffic corridors have long been concentrated near communities that have also been negatively affected by policy choices such as redlining and disinvestment. Black families and lower-income families are more likely to live in neighborhoods where the air is worse and to face higher rates of preterm birth.
My own research has focused on infants with bronchopulmonary dysplasia, or BPD. This is a chronic lung disease that affects many babies born very prematurely. These infants often spend weeks or months receiving respiratory support in the NICU. Even after they leave, their lungs remain vulnerable.
In one Philadelphia study of 378 preterm infants with BPD who were cared for in NICUs affiliated with the Children’s Hospital of Philadelphia, we used a state-of-the-art air pollution model to estimate PM2.5 exposure at each infant’s home address and examined the association of PM2.5 exposure with respiratory illness during the first year after discharge.
What we found was striking because the pollution levels at home were low. In fact, the average exposure was below the long-standing federal annual standard. Yet among infants with the mildest and most common form, grade 1 BPD, each small increase in annual PM2.5 exposure was associated with substantially higher odds of the infant developing a respiratory illness severe enough to require emergency care.
More recently, we followed this same cohort of children through early childhood. We found that higher PM2.5 exposure in the first year after discharge was associated with a higher risk of asthma by the age of 5, an age when many kids enter kindergarten. In other words, what a baby breathes in the months after going home may be associated with respiratory health years later.
The American Lung Association’s 2026 State of the Air report again shows that poor air quality remains a real problem in the Philadelphia region. Those rankings may sound like background noise. Another annual report. Another set of grades. But for my patients, air quality is meaningful. It is part of the discharge plan, whether we name it or not.
What families and policymakers can do
So what do we do? It is tempting to propose individual solutions. Families can use indoor air purifiers. They can avoid outdoor activity on bad-air days. They can keep windows closed during wildfire smoke events.
The Environmental Protection Agency strengthened the annual PM2.5 standard in 2024, lowering it from 12 to 9 micrograms per cubic meter. In practice, the standard establishes a nationwide, health-based benchmark for outdoor air quality and requires states to develop pollution-reduction plans for areas that fail to meet it. That change matters because a growing body of evidence suggests that breathing PM2.5 can harm health even at levels once considered acceptable.
My patients are part of that evidence. Their lungs are telling us that small differences in PM2.5 exposure may matter and that exposure to PM2.5 levels once considered low may have substantial implications for health when infants breathe that air day after day over a long period of time.
There are also local interventions worth taking seriously. Cities can reduce traffic-related emissions near homes, schools and childcare centers. They can electrify municipal vehicle fleets. They can enforce industrial pollution limits. They can invest in high-quality housing. They can also expand tree canopy and green space, which can help capture airborne pollutants and reduce urban heat.
When clinicians discharge a baby from the NICU, we are making a quiet bet that the world outside the hospital will help that child thrive. But decisions made far beyond the bedside shape the quality of the air all children breathe.
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This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Tim Nelin, University of Pennsylvania
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Tim Nelin has received funding from the National Institutes of Health, PolicyLab at the Children's Hospital of Philadelphia, the BPD Collaborative, and the Philadelphia Regional Center for Children's Environmental Health.
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