Particulate Matter (Particle Pollution)

Particulate matter (PM), particulates, or particle pollution are general terms for solid or liquid particles found in the atmosphere; these particles may be of varying sizes and chemical composition. The smaller the particles, the more easily and deeply they can enter our lungs and create health problems.

Regulatory and outreach efforts by EPA, New Hampshire and other states continue to make progress in reducing airborne particulate matter. For more general information about particulate matter, please read EPA’s Particulate Matter Information page.

Health Concerns
Small particles can cause difficulty breathing and sometimes permanent lung damage; they can also affect the heart and cause palpitations and chest pain. Those most sensitive to particle pollution include children, older adults, and people with heart or lung disease.

Types of Particle Pollution
Particle pollution is broken down by particle diameter, measured in micrometers (or microns):

  • Total suspended particles (TSP) consist of all airborne particles, regardless of size.
  • “Coarse” particles (PMcoarse) range from 2.5 to 10 microns in diameter.
  • PM10 describes all particles smaller than 10 microns in diameter.
  • “Fine” particles (PM5) are smaller than 2.5 microns in diameter.

diagram of different sizes of particulate matter

diagram of particulate matter size compared to human hair








Sources of Particle Pollution
Because particle pollution comes from many sources, it comes in many forms. Some particles are directly released into the air by the stirring up of dust by construction activities, paving, driving on unpaved roads, or even the wind. Similarly, smoke from vehicle exhaust, wood and other fuel burning and wildfires emits solid particles into the air. These directly-emitted particles are called “primary” particles. Read What’s in that Smoke?  to learn about the variety of particulates and other pollutants emitted through smoke.

Additionally, “secondary” particles are formed by the chemical reaction of gases, such as sulfur oxides, nitrogen oxides, volatile organic compounds, and ammonia. These gases may come from power plants, cars and trucks, or the burning of any material. Once in the air, they can react to create particles made up of sulfate, nitrate, or carbon. In other cases, gaseous materials can cool into small liquid or solid particles.

Some sources tend to contain a significant amount of the larger particles, PM10, and some release more of the smaller particles, PM2.5. Please see EPA’s Air Emissions Sources page for more about these sources of particle pollution.

Air Quality Forecasts
Small particle concentrations exceeding the “good” classification are common enough in New Hampshire that NHDES provides daily air quality forecasts so you can stay informed and take action to protect your health. When particulate matter or other pollutant levels are expected to reach unhealthy levels, NHDES calls an Air Quality Action Day (AQAD).

New Hampshire air quality forecasts and current  air quality levels are available on the NHDES website, and EPA provides this information nationwide on AirNow. Read more in the NHDES fact sheet Air Quality Information in New Hampshire.

For additional topics related to particulate matter, please click on the links below:
Particle Pollution Attainment Status and Trends
Particle pollution levels currently remain below EPA’s health standards.

State of New Hampshire Air Quality – 2017: Air Pollution Trends, Effects and Regulation
State of New Hampshire Air Quality – 2017: Executive Edition

Particle Pollution Monitoring
Particle pollution monitoring has evolved over the years.

High Particle Pollution Days
Occasionally, particle pollution can get high in New Hampshire; find out when and why.

Keene, a Case Study
Keene has been a focus of particle pollution research and outreach due to high wintertime levels of wood smoke.

Regional Haze
Particle pollution can create a cloudy haze over the landscape, degrading visibility and the enjoyment of natural and scenic areas.