ZmeScience:[2] The findings are based on six years’ worth of mental health outpatient visit data from two major hospitals in Nanjing, China. Nanjing is notorious for its high levels of air pollution, even for China (which has quite a lot of air pollution in general).[3] After comparing the number of visits with records of particulate matter in suspension in the air every day, the authors report that visits were more numerous when air quality was especially poor.[4] The findings, says the team, showcase why we need further investments in mental services, especially as air pollution levels around the world are getting worse.[5] More research is needed to understand how and why air quality influences mental health, they add, but now we know that it can influence how much use specialized services see.[6] Air pollution is the product of many components ranging from carbon monoxide in car exhaust to sulfur dioxide particles from industrial processes. This study focused on particulate matter (PM), tiny pieces of organic materials such as liquids or soil, which are known to pose a threat to human health.
The main danger they pose comes down to their size, which allows PM to enter deep into the lungs. Once there, they can cause quite a lot of damage by ripping through lung tissue and entering the bloodstream.

The team believes that these particles can influence mental health after entering the bloodstream and reaching the brain.