Asthma changes the physical, emotional and academic trajectory of a child’s life. More than 5 million children in the United States have asthma, and every year there are over 750,000 emergency room visits and over 74,000 hospitalizations for asthma among children. Asthma is the leading cause of missed school days each year, and it has been linked to diminished school performance. Although ambient air pollution exposure has long been associated with the worsening of asthma symptoms, mounting evidence indicates that it also leads to the development of asthma among children. 

A recent study found that annually nearly 2 million children worldwide develop asthma due to exposure to nitrogen dioxide (NO₂), a traffic-related air pollutant. Transportation is a key driver of this pollution. Freight trucks and buses make up less than 10% of the vehicles on U.S. roads, but they are responsible for half of the transportation sector’s nitrogen oxide emissions. In some urban areas, 1 in 5 new childhood asthma cases are due to exposure to nitrogen dioxide; in particular neighborhoods, this risk can be twice as high. 

How NO₂ causes asthma

Studies exploring how NO₂ affects the lungs indicate that repeated or long term exposure results in activation of biological pathways that contribute to the development of asthma: secretion of inflammatory cytokines, altered cellular structure, oxidative stress, allergic sensitization, increased mucus formation, airway remodeling and airway hyperresponsiveness. Studies of NO₂ exposure to human bronchial epithelial cells find an increase in pro-inflammatory mediators and inflammation involved in the pathology of asthma.

A growing body of evidence describes the impact of NO₂ on new cases of childhood asthma. It shows consistent and reproducible effects across different cities and populations in North America. Below are a few:

• In studies of Latino and African American children across Chicago, Bronx, Houston, San Francisco and Puerto Rico, a higher average NO₂ exposure during the first year of life was associated with higher odds of being diagnosed with asthma. This was also seen in another study of children in East Boston, Massachusetts.
• Among 1.2 million children in Quebec, scientists found that higher childhood exposures to NO₂ levels at their residential address were linked to increased risk of asthma development.
• A recent study of 4,140 elementary school children (with no history of asthma) in southern California provides particularly strong evidence.  Scientists found that a drop in nitrogen dioxide, over a period of air pollution decline, was associated with a reduction in asthma incidence. This finding was reinforced when using cutting edge causal methods, which found that “childhood asthma incidence rates would have been significantly higher had the observed reduction in ambient NO₂ in southern California not occurred in the 1990s and early 2000s, and asthma incidence rates would have been significantly lower had NO₂ been lower than what it was observed to be.”

These are just a few of the studies that have been done in North America. A systematic review and meta-analysis of 41 studies from around the world investigated the impact of different air pollutants on asthma incidence among children. Of these, 20 studies directly assessed the impact of NO₂, and found that a small increase (4 µg/m3) in NO₂ exposure led to a 5% increase in the risk of developing childhood asthma.

Across these studies, scientists took pains to ensure the findings were not due to other factors like age, sex, race-ethnicity, poverty or smoking in the household. 

We have an opportunity to protect our children’s health

We have an opportunity to protect our children by identifying communities overburdened by NO₂ pollution and its sources. 

First, we need to end the blindspots on NO₂. We must make the true cost of diesel clear through investments in transparency and accountability. New satellite data and community monitoring can help identify pollution hotspots. Robust funding for NO₂ monitoring, analysis and enforcement will enhance existing data to support protective action. The US EPA’s $20 million in grant funding for increased air quality monitoring in communities overburdened by pollution is an important step in this direction.

Better emissions inventories–especially around areas of high truck traffic like ports and warehouses–are important to further illuminate sources and target solutions.

Finally, eliminating harmful pollution from diesel vehicles is crucial. Transitioning to electric school buses, cars and trucks is feasible. New research from EDF finds that by 2027, electric freight trucks and buses will be cheaper to purchase and operate than their combustion engine counterparts. EPA recently proposed stronger pollution standards for medium- and heavy-duty freight trucks and buses, but it needs to go much further in leveraging zero-emitting solutions. Bold clean energy investments by Congress would provide credits to people who purchase electric vehicles, support development of additional charging infrastructure and increase air quality monitoring to ensure that NO₂ doesn’t linger in frontline communities.

We must act now to reduce NO₂ pollution and prevent more asthma every year. The status quo is clearly unacceptable for our children.