PM2.5 refers to particulate matter that is 2.5 micrometers or less in diameter, making it roughly thirty times smaller than that of a human hair, in diameter. Due to this minute size, as well as being able to go down to sizes many microns smaller, it can penetrate deep into the tissue of the lungs upon breathing, causing many health issues to occur.
Additionally, it can also cross into the bloodstream due to its size, making it one of the most dangerous pollutants that can be found in Shasta and throughout the rest of the world. The small air sacs or alveoli that are transport oxygen into the bloodstream instead allow these tiny particles to pass through the blood barrier, allowing them to travel to the furthest reaches of the body.
PM2.5 can be made up of materials such as nitrates and sulfates, dust and soot, various metals, along with other ultrafine materials such as silica and gravel dust. Water and other liquid vapors can also fall under the PM2.5 bracket, along with mold spores and fungi, bacteria, and other dangerous inorganic materials or microorganisms. These all make up the PM2.5 classification, with any material under the 2.5-micrometer size being classed as such, with the more harmful ones being of greater importance in reducing their level in the air.