Faculty Editor: Professor Jeffrey DaCosta

Mental health is a topic that is seemingly everywhere in recent years, as people work on destigmatizing mental health, and building a future where mental illness is accepted and discussed openly. Beyond acceptance, it’s also important to look for ways to improve mental health, and find out if there are specific environmental factors that contribute to the development of mental illness. The strain of mental health on an individual is enormous, and mental illness is increasingly common. In 2016, it was reported that 18.3% of adults had experienced some type of mental illness in their lifetime. Beyond that, the second highest reason for hospitalization of children under the age of 17 in 2015 was mental health disorders.[1]It’s not surprising then, that globally, mental health disorders accrue $1.77 billion dollars in healthcare costs annually.[2]Due to the personal distress it causes, increasing prevalence, and cost, researchers are interested in finding ways to prevent mental illness, rather than only treating it.

Rates of mental illness are increasing at the same time that global societies are becoming more urbanized, which leads to increases in air pollution and rates of  global climate change. Researchers are now studying what environmental factors specifically impact mental health. One major area of research is the effects of air pollution on mental health, and multiple studies have investigated the relationship between particulate matter in the air less than 2.5µm in diameter (PM2.5) and nitric oxide (NO2) gas. Both of these substances are produced from traffic pollution, and are capable of entering the lungs. Susanna Roberts and colleagues performed animal and post-mortem human studies, and found that these air particles are able to enter the bloodstream and cross the blood-brain barrier.[3] This would mean that these particles are capable of interfering with brain functioning and development, which would explain a possible relationship between mental illness and air pollution. Roberts found that air pollution and depression were related, with people who had higher PM2.5 and NO2 blood concentrations reporting more depressive symptoms. However,  ADHD and anxiety rates were not affected.[4]

Another study by Klompmaker and colleagues also studied PM2.5 and NO2 as it relates to mental health by comparing Dutch national health survey results to the environment of where the survey respondents resided. They found that air pollution was linked to generalized poor mental health, while road traffic was not linked to mental health directly, but it was related loosely to anti-anxiety prescriptions. They also found that living near green space, like a park, was inversely related to poor mental health.[5] Similarly, Barton, another researcher, suggested that green space in urban areas can be used to combat mental health. Barton’s research showed that people near green space had less anxiety and depression and healthier cortisol (stress hormone) levels. He suggests that more research should be done on how time in nature and green space can be implemented to treat mental health disorders.[6] This point is especially intriguing given the cost of mental illness, many people don’t seek treatment for mental illness because they can’t afford it, so researching a free and effective way for people to be healthier is important.

Some reviewers, like Ioannidis, argue that the definition of mental health disorders studied are generally too broad and that air pollution causes a variety of health-related problems, so it’s too soon to determine if air pollution and mental illness are directly related.[7] Despite this, it’s important to keep in mind that these early studies are showing that cleaner air could mean less mental illness. Air pollution has been shown to have detrimental effects on the global climate, but we are now realizing it’s affecting human health in ways we didn’t originally anticipate. The combined mental health effects and harm to the environment point towards urgent need for less pollution and global efforts in climate action.


  1. Kioumourtzoglou M. Identifying Modifiable Risk Factors of Mental Health Disorders—The Importance of Urban Environmental Exposures. JAMA Psychiatry.Published online March 27, 201976(6).
  2. Barton, J., & Rogerson, M. (2017). The importance of greenspace for mental health. BJPsych international, 14(4), 79–81.
  3. Susanna Roberts, Louise Arseneault, Benjamin Barratt, Sean Beevers, Andrea Danese, Candice L. Odgers, Terrie E. Moffitt, Aaron Reuben, Frank J. Kelly, Helen L. Fisher, Exploration of NO2 and PM2.5 air pollution and mental health problems using high-resolution data in London-based children from a UK longitudinal cohort study, Psychiatry Research, Volume 272, 2019, Pages 8-17
  4. Roberts, et al.
  5. Jochem O. Klompmaker, Gerard Hoek, Lizan D. Bloemsma, Alet H. Wijga, Carolien van den Brink, Bert Brunekreef, Erik Lebret, Ulrike Gehring, Nicole A.H. Janssen, Associations of combined exposures to surrounding green, air pollution and traffic noise on mental health, Environment International, Volume 129, 2019, Pages 525-537. 
  6. Barton, J., & Rogerson, M. (2017). The importance of greenspace for mental health. BJPsych international, 14(4), 79–81.
  7. Ioannidis JPA (2019) Air pollution as cause of mental disease: Appraisal of the evidence. PLoS Biol 17(8): e3000370.

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