Nearly half of children in the United States are breathing dangerous levels of air pollution, according to a new report, as experts warned Donald Trump’s expansive rollback of protections will make the situation worse.

The 27th annual air quality report from the American Lung Association (ALA) released on Wednesday evaluates pollution across the country by grading levels of ground-level ozone – also known as smog – as well as year-round and short-term spikes in particle pollution, commonly referred to as soot. The report analyzed quality-assured data collected between 2022 and 2024.

It found that 33.5 million children in the US – 46% of those under 18 – live in areas that received a failing grade for at least one measure of air pollution.

The report also found that 7 million children, or 10% of all children in the US, live in communities that failed all three measures.

Speaking to the Guardian, Will Barrett, assistant vice-president of the ALA’s Nationwide Clean Air Policy, said: “Children’s lungs are still developing. For their body size, they’re breathing more air. And also, kids play outdoors, they’re more active, they’re breathing in more outdoor air … So, air pollution exposure in children can contribute to long-term developmental harm to their lungs, new cases of asthma, increased risks of respiratory illness and other health considerations later in life.”

The report further found that communities of color are disproportionately exposed to unhealthy air. As a result, they are more likely to live with one or more chronic health conditions that make them more vulnerable to pollution, including asthma, diabetes, and heart disease.

Although people of color make up 42.1% of the US population, they represent 54.2% of those living in counties with at least one failing grade, the report noted. It also found that a person of color is 2.42 times more likely than a white person to live in a community that fails all three pollution measures.

Smog remains the most widespread pollutant affecting Americans’ health. Between 2022 and 2024, 38% of the US population – approximately 129.1 million people – were exposed to ozone levels that put their health at risk. This marks the highest number recorded in the ALA’s report in six years, and a 3.9 million increase from the previous year.

Several factors contributed to these unhealthy pollution levels, including extreme heat, drought and wildfires which have exposed a growing share of the population to harmful ozone, the report said.

The regions most affected by high ozone levels include south-western states from California to Texas, as well as much of the midwest. This is mainly driven by smoke from Canada’s 2023 wildfires crossing into the US, along with high temperatures and weather patterns that favored ozone formation in 2023 and 2024 – particularly in southern states.

More broadly, the report found that climate change is intensifying ozone pollution by boosting precursor emissions and creating atmospheric conditions such as higher temperatures and lower wind speeds that allow pollutants to build up and ozone to form.

The report also highlighted datacenters as a growing source of air pollution. In recent years, datacenters have consumed roughly 4.4% of total US electricity, a figure that could rise to as much as 12% within the next decade.

Their impact stems largely from reliance on regional electricity grids where fossil fuels such as methane gas and coal still account for a large portion of generation, the report said. In addition, many datacenters use dozens of large diesel-powered backup generators, which emit carcinogenic particulate matter.

“As the demand for increases in datacenters continues to grow, the focus needs to be on non-combustion, clean renewable energy sources that are additive and not taking away from the grid,” Barrett said.

He also pointed to a series of environmental rollbacks by the current Environmental Protection Agency, warning that they are putting air quality at greater risk.

“There’s a devaluing of children’s health by this EPA as they are weakening, delaying and repealing critical health protection,” he said, pointing to reversals including “missing deadlines for particle pollution standards, repealing vehicle standards, repealing EPA’s responsibility for protecting health against climate pollution, and even allowing for increased emissions of pollution from oil and gas facilities”. He also cited mercury – a toxic air contaminant released from coal plants – as a key concern.

“[There is] a wide-scale effort by the federal EPA to eliminate health protections while also distancing themselves from their own mission to protect public health,” Barrett added.

Since returning to office last year, the Trump administration has initiated at least 70 actions to roll back environmental and climate protections. Among them is the loosening of regulations on power plants that limit mercury and other hazardous air toxics.

Other rollbacks include overturning limits on major air pollution sources, disbanding EPA advisory committees on air quality and ending the practice of estimating the monetary value of lives saved by limiting fine particulate matter and ozone while still calculating costs to companies.