Particulate Matter (PM) (or soot) are microscopic solid particles or liquid droplets that are either emitted directly into the air or formed by pollutants that combine in the atmosphere. PM is usually measured in three size ranges: PM10, PM2.5, and PM1 PM10 (or coarse dust particles) are about 30 times smaller than the width of a human hair and are small enough to pass through the barrier formed by your nose hair and get into your lungs. PM10 includes Crushing/grinding operations, dust stirred up by vehicles, pollen, mold, and plant and insect particles are considered. A dangerous level of PM10 is 125 μg/m³ (microgram per cubic meter) or more. Emissions from all types of combustion, such as motor vehicles, power plants, residential wood burning, wildfires, agricultural burning, and some industrial processes produce PM2.5 (or fine particles). PM2.5 is dangerous because it can transfer from your lungs into your bloodstream and end up anywhere in your body: that’s why it is also called “the invisible killer”. A dangerous level of PM2.5 is 90 μg/m³ or more. PM1 is a major subset of PM2.5, and consists of extremely fine particles that are even more likely to reach deeper into the respiratory system than PM2.5. PM1 is emitted into the atmosphere from sources such as factories, vehicular pollution, construction activities, and road dust and it remains suspended in the air you breathe. A dangerous level of 1 is 61μg/m³ or more.