PM stands for particulate matter (also called particle pollution): the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope. Particles are defined by their diameter for air quality regulatory purposes.
The number after PM indicates the size of the particles in microns. The different sizes of PM are:
PM10 : inhalable particles, with diameters that are generally 10 micrometers and smaller
PM2.5 : fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller.
How small is 2.5 micrometers? Think about a single hair from your head. The average human hair is about 70 micrometers in diameter - For example, making it 30 times larger than the largest fine particle. For example, second-hand smoke indoors. PM 2.5 can stay in the atmosphere for a long time and can enter the body via respiration, accumulate in the trachea or lungs, and affect human health. PM2.5 particles are larger than viruses and smaller than bacteria, and can carry toxic substances into the human body.
PM1: extremely fine particulates with a diameter of fewer than 1 microns.
PM1: measures particulate pollutants smaller than 1 micron. Like other fine particles, it can cause damage to the heart, lungs, and other organs.
