A CIESE Realtime Data Project

LEARN MORE: Sources of Particulate Matter


Particulate matter, or PM, is the term for particles found in the air, including dust, dirt, soot, smoke, and liquid droplets.  Particles can be suspended in the air for long periods of time.  Some particles are large or dark enough to be seen as soot or smoke.  Others are so small that individually they can only be detected with an electron microscope.

Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. These solid and liquid particles come in a wide range of sizes. Particles less than 10 micrometers in diameter (PM10) pose a health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter (PM2.5) are referred to as "fine" particles and are believed to pose the greatest health risks. Because of their small size (approximately 1/30th the average width of a human hair), fine particles can lodge deeply into the lungs.

Where does PM2.5 come from?
Sources of fine particles include all types of combustion activities (motor vehicles, power plants, wood burning, etc.) and certain industrial processes. Particles with diameters between 2.5 and 10 micrometers are referred to as "coarse." Sources of coarse particles include crushing or grinding operations, and dust from paved or unpaved roads. Other particles may be formed in the air from the chemical change of gases. They are indirectly formed when gases from burning fuels react with sunlight and water vapor. These can result from fuel combustion in motor vehicles, at power plants, and in other industrial processes.

What are the health effects of PM2.5?
Health studies have shown a significant association between exposure to fine particles and premature death. Other important effects include aggravation of respiratory and cardiovascular disease (as indicated by increased hospital admissions, emergency room visits, absences from school or work, and restricted activity days), lung disease, decreased lung function, asthma attacks, and certain cardiovascular problems such as heart attacks and irregular heart beat. Individuals particularly sensitive to fine particle exposure include older adults, people with heart and lung disease, and children.

What goes up must come down...eventually.
What happens to the pollutants and particles when they are released from their sources? Once released into the air, pollutants can be directly inhaled, pollutants can settle back on to the ground (dry deposition) or mix with rain water to create acid rain (wet deposition). These pollutants include, but are not limited to, sulfur dioxide, nitrogen oxides, ammonia, and mercury.

Acid rain also reduces how far and how clearly we can see through the air, an effect called visibility reduction.  Acid rain and the dry deposition of acidic particles contribute to the corrosion of metals (such as bronze) and the deterioration of paint and stone (such as marble and limestone). These effects seriously reduce the value to society of buildings, bridges, cultural objects (such as statues, monuments, and tombstones), and cars.

Who is most at risk?
Roughly one out of every three people in the United States is at a higher risk of experiencing PM2.5 related health effects. One group at high risk is active children because they often spend a lot of time playing outdoors and their bodies are still developing. In addition, oftentimes the elderly population are at an increased risk. People of all ages who are active outdoors are at increased risk because, during physical activity, PM-2.5 penetrates deeper into the parts of the lungs that are more vulnerable to injury.