What Is Particulate Matter?
What Particulate Matter Is
Particulate matter (PM) is small particles of solids or liquid droplets. It comes from smoke, dust, fly ash and condensed vapors that are released or kicked up into the air.
PM10 stands for particulate matter that is 10 microns in diameter or smaller. PM2.5 stands for particulate matter measuring 2.5 microns in diameter or smaller. A micron is very small. For example, a human hair is about 70-100 microns in diameter. 2.5 microns is about the size of a grain of flour.
What Particulate Matter Is Not
The U.S. Environmental Protection Agency considers six ‘criteria pollutants’ as serious potential health threats for people. Particulate Matter is one of those six criteria pollutants. The other five are not particulate matter:
- Carbon Monoxide is a colorless, odorless gas that results from combustion – primarily from cars and trucks.
- Nitrogen Dioxide is a reddish brown gas that is formed as a byproduct of fuel combustion.
- Sulfur Dioxide is a colorless gas with a pungent odor that, in Arizona, has historically been produced from the smelting of copper oxide ore and also from burning gasoline and diesel fuel which contain sulfur.
- Ozone is a colorless and mostly odorless gas that is a natural and beneficial component of the upper atmosphere. At ground level, ozone is a respiratory irritant that forms from a photochemical reaction from sunlight reacting with fumes from fuel, paint, cleaners, tailpipes and vegetation. Ozone pollution is typically worse in summer. Visit the ozone section of this website to learn what's being done and what you can do to reduce ozone pollution.
- Lead was, at one time, used as a gasoline additive, which resulted in high lead air pollution levels. Lead is no longer used as a gasoline additive in the United States.
Particulate Matter and Winter
Particulate matter is at its worst during the winter in the Valley. This is because the cooler air at ground level becomes trapped by a layer of warmer air above, creating a temperature inversion. This inversion also traps pollutants close to the ground, which increases the chances of particulate matter reaching unhealthy levels.
Did You Know?
- Even healthy people feel the effects of high amounts of particulate matter in the air. Children, the elderly, and people with heart or lung disease, like asthma, are especially likely to have problems. One of the reasons you can’t see the distant – and not so distant – mountains may be because of high amounts of particulates. Learn more about how particulate pollution affects you.
- Particulate matter is worst during the winter. Find out what's being done about particulate pollution.
- You really can do something to make a difference about particulate pollution.