What is PM 2.5 & PM 10 and Why Should You Care?

PM2.5 refers to atmospheric particulate matter (PM) that have a diameter of less than 2.5 micrometers, which is about 3% the diameter of a human hair. PM 10 is a size less than 10 micrometers. The image below shows a comparison of the sizes.

Air Quality Size

For more details see WikiPedia