Air PollutionAir Quality

“Safe” Levels of Air Pollution Negatively Affect Brain Development and Function, According to 2023 Studies

By August 4, 2023 No Comments
10–12 minutes to read

Following the Clean Air Act in 1970, the EPA has been required to set and regularly review air pollution standards indicating what levels of six hazardous pollutants humans and the environment can safely be exposed to. The National Ambient Air Quality Standards (NAAQS) are based on established scientific research and inform legislation at all levels. 

However, two recent studies have found that exposure to levels of pollution within the EPA’s “safe” standards may be linked to negative effects on the structure and function of the brain. Continue reading to learn about these studies and their implications. 

What Levels of Air Pollution Are Considered Safe by the EPA? 

The six pollutants targeted by the Clean Air Act are carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), and sulfur dioxide (SO2). These pollutants are both notably harmful to humans and the environment and are common across the United States. 

The NAAQS defines primary standards, which indicate the concentrations of each pollutant that are harmful to human health (particularly the health of people with existing respiratory conditions, children, and the elderly), as well as secondary standards, which indicate pollution levels that affect other important factors such as visibility, damage to livestock, crops, and ecosystems, and building corrosion. 

The primary standards are as follows: 

Carbon monoxide: 

  • 9 ppm (parts per million), 8-hour average 
  • 35 ppm, 1-hour average 


  • 0.15 μg/m3 (0.15 microgram/millionth of a gram per cubic meter of air),3 month average 

Nitrogen dioxide:

  • 100 ppb (parts per billion), one-hour average
  • 53 ppb, annual mean


  • 70 ppb, 8-hour average

PM2.5 (particulate matter with a diameter of 2.5 micrometers or less):

  • 12 μg/m3, annual mean
  • 35 μg/m3, 24-hour average

PM10 ( (particulate matter with a diameter of 10 micrometers or less):

  • 150 μg/m3, 24-hour average

Sulfur dioxide: 

  • 75 ppb, 1-hour average

Study: Safe Levels of Air Pollution Harm Children’s Brain Development

A 2023 study published in the peer-reviewed journal Environment International by researchers from the Keck School of Medicine at the University of Southern California used brain scan data from the Adolescent Brain Cognitive Development (ABCD) study to examine the relationship between brain connectivity and pollution exposure. 

Using EPA and other air quality data, the researchers calculated the levels of ozone, nitrogen dioxide, and particulate matter that each of the 9497 children were exposed to. Brain scans taken at age nine or ten were compared to follow-up scans from two years later. 

After controlling for other factors such as socioeconomic status that may affect brain development, researchers found that brain connectivity in several regions of the brain was affected by exposure to more pollution; this effect was present even at levels of pollution considered safe by the EPA. 

Nitrogen dioxide exposure was associated with a decrease in connectedness between brain regions, while PM2.5  was associated with increased connectivity. Ozone was associated with increased connectivity within the cortex (the outermost layer of the brain, which is responsible for high-level executive functions, such as memory, problem-solving, impulse control, and perception of sensory data), but exposure to ozone was also associated with decreased connectivity between the cortex and other regions of the brain such as the hippocampus (associated mainly with memory; damaged to the hippocampus is present in a range of psychiatric disorders) and the amygdala (associated with emotions). 

It is important to remember that greater brain connectivity is not always better, especially in pre-adolescent children, because any deviation from normal development at this critical stage of brain growth can have lifelong consequences. 

Study: Brief Air Pollution Exposure Has Immediate Negative Impacts on the Brain 

Another study, published in the peer-reviewed journal Environmental Health, found instant effects of pollution exposure on the brains of healthy adults. Researchers from the University of British Columbia and the University of Victoria exposed 25 healthy participants in double-blind conditions to levels of diesel pollution commonly found in areas with heavy traffic, and to clean, filtered air at separate times.

Brain activity was measured using fMRI (functional magnetic resonance imaging) scans before and after each two hour exposure, with two weeks between each trial. The fMRI scans showed a decrease in functional connectivity in regions of the brain known as the default mode network, which is most active during passive, internal tasks such as recalling and thinking about the future. 

Altered function in the default mode network has been linked to reductions in cognitive abilities and symptoms of depression. These findings highlight that it’s not just the smoggy, hazy days following events such as wildfires and train derailments that we should be concerned about; short-term air pollution exposure at levels encountered every day by many people can have significant health and cognitive effects. 

Indoor Air Purifiers Reduce Pollution Exposure

Reducing levels of harmful pollutants in outdoor air is a long-term effort, and, particularly for those living in urban and industrial areas, avoiding ambient exposure to pollution is not possible. 

However, with the average American spending at least 90% of their time indoors, ensuring that homes, offices, schools, and other buildings are protected from pollutants can help minimize the volume of pollutants inhaled. 

To effectively protect yourself against harmful pollutants, use a premium air filter that uses both factory-tested and certified HEPA filters (which trap particulate matter) and activated carbon filters (which remove gaseous pollutants such as ozone, sulfur dioxide,, and nitrogen dioxide). 

Learn more: Camfil’s Medical-Grade City M Air Purifier

About Camfil Clean Air Solutions

For more than half a century, Camfil has been helping people breathe cleaner air. As a leading manufacturer of premium clean air solutions, we provide commercial and industrial systems for air filtration and air pollution control that improve worker and equipment productivity, minimize energy use, and benefit human health and the environment. We firmly believe that the best solutions for our customers are the best solutions for our planet, too. That’s why every step of the way – from design to delivery and across the product life cycle – we consider the impact of what we do on people and on the world around us. Through a fresh approach to problem-solving, innovative design, precise process control, and a strong customer focus we aim to conserve more, use less and find better ways – so we can all breathe easier.

The Camfil Group is headquartered in Stockholm, Sweden, and has 30​ manufacturing sites, six R&D centers, local sales offices in 35+ countries, and about 5,600 employees and growing. We proudly serve and support customers in a wide variety of industries and in communities across the world. To discover how Camfil USA can help you to protect people, processes and the environment, visit us at 



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