PM 2.5


Particulate matter, or PM, is the term for particles found in the air, including dust, dirt, soot, smoke, and liquid droplets.  Particles less than 2.5 micrometers in diameter (PM 2.5) 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.

Sources of fine particles include all types of combustion activities (motor vehicles, power plants, wood burning, etc.) and certain industrial processes. Distant sources such as coal-fired power plants are significant contributors to the PM 2.5 in the Roanoke Valley. The primary chemical constituents of outdoor particles are sulfate, nitrate, organic and black carbon.

Roughly one out of every three people in the United States is at a higher risk of experiencing PM 2.5 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 is at 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.

Particulate Matter is a year around problem. Current PM 2.5 levels and daily Air Quality Index (AQI) forecasts can be found on the Virginia DEQ website.

Particulate Matter . . .

  • is associated with serious health effects.
  • is associated with increased hospital admissions and emergency room visits for people with heart and lung disease.
  • is associated with work and school absences.
  • is the major source of haze that reduces visibility in many parts of the United States, including our National Parks.
  • settles on soil and water and harms the environment by changing the nutrient and chemical balance.
  • causes erosion and staining of structures including culturally important objects such as monuments and statues.

Health problems for sensitive people can worsen if they are exposed to high levels of PM for several days in a row.   Many scientific studies have linked breathing PM to a series of significant health problems, including:

    • aggravated asthma
    • increases in respiratory symptoms like coughing and difficult or painful breathing
    • chronic bronchitis
    • decreased lung function
    • premature death

The table below shows the AQI for PM 2.5:


Particulate Matter Standards

There are two PM 2.5 health standards including the 24-hour average standard and the annual arithmetic mean standard.

24-hour average standard (strengthened in 2006): The 3-year average of the 98th percentile values at each monitoring site is less than or equal to 35.4 micrograms/cubic meter. The 24-hour average standard is based on 3 consecutive, complete years of air quality data.

Annual arithmetic mean standard (strengthened in 2012): Spatially, the average annual means are less than or equal to 12.0 micrograms/cubic meter. The 3-year average of the spatially averaged annual means is determined by averaging quarterly means at each air quality monitor to obtain the annual mean PM 2.5 concentrations, then averaging across all designated monitors, and finally averaging 3 consecutive years. A region would be out of compliance if its air contained higher PM 2.5 concentrations, on average, than the health standard for three years. The EPA refers to the 3-year average as the Design Value.

PM 2.5 in the Roanoke Valley:

Meeting the Particulate Matter Standards:  The Roanoke Valley has two PM 2.5 monitors which determine compliance.  Both monitors are in compliance for both the annual mean and the 24-hour standards.

Below are charts that display the Design Value for both Salem and Roanoke, in terms of PM 2.5:


Particulate Matter from Wildfires

Published in the Journal of the American Heart Association, researchers analyzed data from the 2006-2007 wildfires in Victoria, Australia. What the team found was nearly a seven percent increase in heart attacks when the surrounding air was filled with smoke from the fires.

The majority of the increased risk was in elderly patients (ages 65 and older), and the researchers studied data from hospital admissions, emergency room visits and out-of-hospital heart attacks.

Incident rates spiked after two days of wildfire smoke exposure at PM2.5 concentrations. Men had the highest risk factor for out-of-hospital heart attacks while women were at greater risk for ischemic heart disease hospital admissions.


2 Responses to PM 2.5

  1. Pingback: Yellow Air Quality for Particulates Today | Breathe Roanoke

  2. Gary Hillard says:

    I’m concerned about the impact of coal trains on PM 2.5 in Roanoke. Research in other states draws a direct connection between closeness to coal trains and increased hazards in air quality. Measuring air quality in Roanoke out by the Valley View Mall would fail to show much of the coal train impact on air quality in much of SE and the other neighborhoods close to coal train traffic. I would ask that air be sampled near the trains, and would volunteer my house or yard on 6th Street SE as a location for that sampling.

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