Currently looking at the health effects of PM 2.5.
The size of particles is directly linked to their potential for causing health problems. Small particles less than 10 micrometers in diameter pose the greatest problems, because they can get deep into your lungs, and some may even get into your bloodstream. (EPA) https://www.epa.gov/pm-pollution/health-and-environmental-effects-particulate-matter-pm
Interesting report. “Health Effects of Particulate Matter”:
http://www.euro.who.int/__data/assets/pdf_file/0006/189051/Health-effects-of-particulate-matter-final-Eng.pdf