Air pollutants, such as smog, soot, greenhouse gases and other chemicals, have long been known to be harmful to human health and to the environment.

The World Health Organization has approximated that at least 4.6 million people worldwide die each year as a result of illness attributable to air pollution.

In 1970, the U.S. Environmental Protection Agency authorized the Clean Air Act, which is meant to protect the public health by regulating the amount of harmful air pollutants that can be released into the air.

“Most air pollution comes from energy use and production,” said John Walke, director of the Clean Air Project, part of the Climate and Clean Energy Program of the NDRC. “Burning fossil fuels releases gases and chemicals into the air.”

According to Walke, air pollution is a destructive feedback loop that contributes to climate change and also results from climate change.

Scientists have long been determined to find out about the ways that air pollution can impact human health and what contributes to it.

According to NASA, a large percentage of air pollutants come from particles released into the air by car and truck exhaust, factories, dust, pollen and mold spores, as well as natural disasters, such as volcanoes and wildfires.

An article published by the Environmental Defense Fund distinguishes the different types of air pollution.

Particulate matter consists of small particles, such as dust, soot and drops of liquids. A majority of these particles found in urban areas directly form from the burning of fossil fuels, automobiles, nonroad equipment and industrial factors.

Coarse particulate matter (PM₁₀) is linked to nasal and upper respiratory tract health problems, such as the common cold, sinusitis and bronchitis.

While air pollution is associated with a variety of respiratory problems, recent research has shown that the mental health of children is impacted by air pollution. In fact, studies done on fine particles, also known as PM₂.₅, have found that higher exposure on can impair brain development in children.

“This is the first study showing how air pollution exposures affect depressive symptoms as well as the interrelationship between the symptoms and subsequent memory decline that had not been found in older people aged less than 80 years,” said Andrew Petkus, assistant professor of clinical neurology at the University of Southern California.

In his study, Petkus’ team found that long-term exposure to chemicals such as nitrogen dioxide or fine particulate pollutants was associated with an increase in the expression of certain depressive symptoms.

A group of Researchers led by Sheba M J MohanKumar, reported that depressive symptoms are a direct result of the inflammation and oxidative stress in the brain.

More specifically, a long-term study done by researchers at Duke University revealed that childhood air pollution exposure is linked to mental distress and dysfunction at the age of 18.

Aaron Reuben, the first author of the study, indicated that there is a link between exposure to pollutants and psychiatric disease.

Randy Nelson, professor of neuroscience at the Ohio State University, experimented on the effects of air pollution using a mouse model.

Through this study, he found that the mice who were exposed to pollutants showed an equivalent form of depression.

Additionally, Nelson discovered that there were physical changes to the nerve cells in the hippocampus of the mouse.

In MRI scans done on children, it was revealed that those who were exposed to urban pollution had a higher chance of having brian inflammation and damaged tissue in the prefrontal cortex.

Other animal and human based studies have shown that being exposed to particulate matter causes oxidative stress, a condition in which there is an imbalance in the production of reactive oxygen species and antioxidant defenses.

As a result of oxidative stress, the normal production of cortisol is interrupted when the hypothalamic-pituitary-adrenal axis is disrupted.

These studies have also supported the claim that depending on the individual’s medical and psychiatric history, particulate matter can cause inflammation of the central nervous system, increasing the chances that someone would develop depression, anxiety disorders, bipolar disorder or other mental health problems.

In addition to psychiatric problems, these pollutants may also have a long-term effect on the subjective feelings of well-being, although not much is known about whether exposure to particulate matter will result in chronic stress, normal cognitive performance or aid in the development of schizophrenia and dementia.

Future research studies are aimed at determining if air pollution can result in neurocognitive disorders, such as dementia and schizophrenia, and if there is a greater effect on those of different socioeconomic status.