This study found high particulate matter from pollution may activate the nervous-hormone system in the body [hypothalamus-pituitary-adrenal glands] to produce more stress hormones such as cortisol. Indoor air purification was found to reduce stress hormones in this study. Another reason to visit the country more often for some fresh air.
Huichu Li, Jing Cai, Renjie Chen, Zhuohui Zhao, Zhekang Ying, Lin Wang, Jianmin Chen, Ke Hao, Patrick L. Kinney, Honglei Chen, Haidong Kan. Particulate Matter Exposure and Stress Hormone Levels. A Randomized, Double-Blind, Crossover Trial of Air Purification. https://doi.org/10.1161/CIRCULATIONAHA.116.026796
Circulation. 2017;136:618-627 http://circ.ahajournals.org/content/136/7/618