The Damaging Effects of Air Pollution on Mental Health

June 24, 2022

Abigail Lindner

For four years, I lived in a high-density city in central China. Over the past fifty years, China has undergone rapid industrial expansion, growing its GDP at an unprecedented rate. While this expansion has benefited its economy, it has been damaging to the natural environment. The most prominent manifestation of this damage was the quality of the air. Having lived in suburban areas removed from immediate traffic or factory work until that point, the smog shocked me at first, but in time it became a common background feature.

What is Air Pollution?

Air pollution is defined by the World Health Organization (WHO) as “contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere.” Particularly prevalent and harmful culprits include ground-level ozone, particulate matter (PM), carbon monoxide, lead, sulfur dioxide, and nitrogen dioxide, all of which the EPA’s National Ambient Air Quality Standards (NAAQS) regulate.

Air pollution, a worldwide problem, has displaced consumption of contaminated water as the greatest environmental health hazard for humans. Approximately 80% of modern-day air pollution is caused by fossil fuel combustion by automobiles. In addition to being the main source of urban pollution, transportation-related air pollution is associated with the most serious health outcomes. According to the Environmental Protection Agency (EPA), while concentrations of hazardous air pollutants have dropped considerably since 1990, over 102 million people in the United States, accounting for about 30% of the population, live in counties with pollution levels that exceed the NAAQS for 2021.

How Does Air Pollution Affect Human Health?

More is known about the physical effects of air pollution on human health than the mental effects. For instance, in 2012, 7 million premature deaths can be attributed to air pollution exposure. Consistent and significant associations have been drawn between exposure to air pollution and adverse respiratory and cardiovascular health. Given the complexity of environmental influences, it is often difficult to conclude causation, but the associations detected are buttressed by additional studies that discovered that improvements in air quality yielded almost immediate improvements in public health. These physical measures are easier to quantify than the measures for assessing the impact of air pollution on mental health. However, emerging research on this relationship is promising.

Economic growth threatens environmental features, the loss of which negatively impacts human happiness. This reality ties into the Easterlin paradox, which states that “at a point in time happiness varies directly with income, both among and within nations, but over time the long-term growth rates of happiness and income are not significantly related.” China is a good example of this. Despite incredible growth in the last few decades, subjective well-being (SWB), as measured by the Chinese General Social Survey, has stagnated.

There are two main dimensions to explore in this discussion of air pollution and mental health: 1) happiness and well-being; and 2) psychotic and psychiatric disorders. The associated questions might be expressed “How is a person’s subjective happiness and well-being affected by exposure to air pollution?” and “What impact, if any, does air pollution have on the incidence of psychotic and psychiatric disorders in people exposed to it? 

Happiness and Well-Being

To answer the first question regarding happiness and well-being, Dr. Jackson G. Lu, Assistant Professor of Work and Organization Studies at the MIT Sloan School of Management, conducted a systematic review of journal articles from Australia, Canada, China, the United States, and Europe that examined, among other dimensions, the psychological effects of air pollution. Across the world, self-reported measures and social media data found that air pollution negatively predicted happiness and life satisfaction.

For one example, in 2017 three scholars from Beijing Normal University, Peking University, and Yale University published research on a nationwide longitudinal survey that gauged Chinese residents’ hedonic (moment-to-moment) and evaluative (longer-term) happiness in relation to the presence of air pollution. The researchers used data from the 2010, 2012, and 2014 China Family Panel Studies (CFPS), a nationally representative survey that captures, among other measures, life satisfaction, depressive symptoms, and hedonic unhappiness. They also used interpolated air quality indices (API) from the Ministry of Environmental Protection of China and weather data from the National Climatic Data Center. By matching CFPS data with city-level API data, the researchers could approximate the effect of air quality on the mental well-being of people in China. The conclusion was that, while life satisfaction did not vary, greater air pollution correlated with reduced hedonic happiness and increased depressive symptoms.

Drawing another example from Lu’s review: In an innovative 2019 study published in Nature Human Behavior, a research team led by Dr. Siqi Zheng of MIT combined the daily air quality index and daily real concentration data of PM2.5 for 144 Chinese cities in 2014 with 210 million geotagged microblog posts from the Chinese microblog social media platform Weibo. A semantic analysis tool measured the daily happiness expressed in these millions of posts. By considering these data dimensions and many data points together, the researchers found that, among people living in cities, high levels of air pollution predicted low reported levels of happiness.

Psychotic and Psychiatric Disorders

Answering the second question, on psychotic and psychiatric disorders, is more difficult because of the complex mixture of genetic and environmental factors already involved when picking through diagnoses. Still, existing research suggests that air pollution may contribute to the emergence or aggravation of depression, dementia, anxiety, and suicidal ideations. The proposed mechanisms for such an effect include damage to the brain, inflammation from the potent inflammatory properties of air pollutants, and oxidative stress, the last of which is also associated with the negative physical effects of air pollution.

One noteworthy study on the possible link between air pollution and mental disorders involved a collaboration of researchers from universities in Denmark and the United States. Two datasets were used, one for each country: the IBM Health MarketScan Commercial Claims and Encounters Database for the United States and the Danish national treatment and pollution registers for Denmark. The former spans the years 2003 to 2013 and comprises the insurance claims of over 150,000,000 unique individuals; the latter contains over 1,400,000 unique individuals born in Denmark between 1979 and 2002, inclusive, and living in Denmark by their 10th birthdays. Air quality data came from the EPA’s Environmental Quality Index for the U.S. analysis and the Danish air quality dispersion modeling system THOR and two regional models for the Denmark analysis. 

For the U.S. cohort in this collaborative study, county-level statistical analysis suggested that, after ethnic composition of a population, air quality was the strongest predictor of an individual being diagnosed with bipolar disorder - an approximately 27% increase in probability. For the Denmark cohort, individual-level analysis suggested that the rate of bipolar disorder, schizophrenia, personality disorder, and depression increased as air pollution exposure increased. The incidences of schizophrenia and personality disorder were especially affected, with incidence of diagnosis rising 148% and 162%, respectively, between the lowest air pollution exposure and the highest. For potential biological mechanisms, the researchers discussed the possibility of “inflammatory and cytotoxic damage to neural tissues,” one of the common hypotheses mentioned previously.

Conclusion

That air pollution is harmful to human health is uncontested. Recent research contributes another dimension to decades-long concerns by tracing links to adverse mental health and poor air quality. Discouragingly, air pollution is not a problem that can be solved by the joint force of individuals. The decline in air pollutant concentration in the United States in the second half of the 20th century is creditable to regulations placed at the federal level. As fossil fuel combustion is responsible for over three-quarters of the air pollution today, the most powerful, effective policies will reduce dependence on fossil fuels.

Until change materializes, individuals living or working in areas with unhealthy levels of air pollution exposure (and it could be argued that there is no healthy level of air pollution exposure) have options to mitigate its effects on their health, physical and mental. Recommendations include use of personal protective equipment, such as well-fitted, multi-layered facemasks; route planning that minimizes near-road air pollution exposure; moderate physical activity to strengthen respiratory and cardiovascular health; and adoption of clean fuels and efficient ventilation and cookstoves in the household. 

To learn about current air quality in Massachusetts, visit MassAir Online and IQAir. To learn about your zip code, search on AirNow. 

Thumbnail photo credit: Pixabay from Pexels

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