A micron, also known as (µm), is a small unit of measurement that measures length. It is another name for micrometer, which is one-thousandth of a millimeter, or one-millionth of a meter. Airborne particles are usually described in microns.
Generally speaking, the human eye can see debris and dust that are approximately 25 microns in size. Particles smaller than 0.3 microns are considered to be ultrafine particles. Ultrafine particles penetrate deep into the lungs. The concentration of these particles is higher, making them harder for the lungs to deal with, leading to inflammation.
Ultrafine particles are small enough to enter the cells in the body and end up in the bloodstream, potentially causing heart and brain diseases. Children, elderly people, and people with lung problems like asthma are especially vulnerable to ultrafine particle air pollution.