"Particulate matter," also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, soil or dust particles, and allergens (such as fragments of pollen or mold spores).The size of particles is directly linked to their potential for causing health problems. Particulate matter less than 10 micrometers in diameter pose the greatest problems because these particles can deposit deep into the lungs.
The National Ambient Air Quality Standards (NAAQS) listed below for particulate matter address two categories of particle pollution: "inhalable coarse particles" (PM10) and "fine particles" (PM2.5). Inhalable coarse particles (PM10) are those that are larger than 2.5 micrometers but are 10 micrometers in diameter or less (PM10) and is associated primarily with road dust. Fine particles are those that are 2.5 micrometers in diameter or less (PM2.5) and are generated from residential wood burning, road dust, and fossil fuel combustion. Even though local sources (such as wood smoke emissions) contribute to PM2.5 concentrations, statewide levels are frequently influenced by the transport of these fine particulates from out of state sources, such as ongoing forest fires many miles upwind.
Pollutant Measure Standards
Pollutant | Averaging Time | NAAQS |
|---|---|---|
| PM10 | 24-hour | 150 µg/m3 |
| PM2.5 | Annual Arithmetic Mean | 12 µg/m3 |
| PM2.5 | 24-hour | 35 µg/m3 |
There are a large number of health studies that link exposure to fine particles (i.e., PM2.5) at levels measured in the ambient air with a variety of heart and respiratory diseases. Long-term exposures, such as those experienced by people living in areas with high particle levels for many years, have been associated with problems such as reduced lung function and the development of chronic bronchitis and even premature death. Short-term exposures to particles (hours or days) can aggravate lung disease, causing asthma attacks and acute bronchitis, and may also increase susceptibility to respiratory infections. In people with heart disease, short-term exposures have been linked to heart attack and arrhythmias. Healthy children and adults have not been reported to suffer serious effects from short-term exposures, although they may experience temporary minor irritation when particle levels are elevated. However, people with heart or lung disease, older adults, and children are considered at greater risk from particles than other people, especially when they are physically active. Exercise and physical activity cause people to breathe faster and more deeply and therefore take more particles into their lungs.
PM2.5 outdoor air quality measures are available in a number of formats, including monitored (only) in counties where monitors are located, as well as monitored and modeled (combined) and modeled (only) for all counties, communities, and census tracts. In addition to annual average PM2.5 concentrations, daily outdoor air quality measures are also available. The daily measures include percent of days exceeding the daily PM2.5 NAAQS as well as information on the number of people exposed to levels of PM2.5 pollution above the NAAQS. When comparing across geographies, a higher number of person-days indicates an area with a larger exposed population and a larger number of high pollution days.
What is particulate matter?
Particulate matter, which is also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including chemicals, metals, and soil or dust particles. The size of the particles is directly related to their potential for causing health problems. Particulate matter is grouped into three size categories: PM10, PM2.5, and ultrafine particles. Particles that are 10 micrometers or less in diameter (PM10) are of the most concern because they can pass through the nose and throat and enter the lungs. Fine particles, also known as PM2.5, are 2.5 micrometers in diameter and smaller. Ultrafine particles are smaller than 100 nanometers. Currently outdoor air quality regulations exist for PM10 and PM2.5.
What is PM2.5?
PM2.5 refers to "fine" particulate matter that is 2.5 micrometers in diameter and smaller; in comparison, the average human hair is about 70 micrometers. Sources of particulate matter are primarily the result of combustion activities (e.g., residential wood burning, fossil fuel combustion) or formed from chemical reactions of gaseous pollutants in the atmosphere. Fine particles can be a local pollutant but also are considered regional pollutants because they can be suspended in the atmosphere for long periods of time and transported over long distances. Fine particles are also the major cause of haze or reduced visibility.
Why is PM2.5 an important public health issue
Fine particles pose the greatest risk to health because scientific studies have linked particle pollution, especially fine particles that can deposit deep into the lungs, with increased respiratory symptoms, such as irritation of the airways, coughing, or difficulty breathing; decreased lung function; aggravation of lung disease, causing asthma attacks and acute bronchitis; irregular heartbeat; nonfatal heart attacks; and premature death in people with pre-existing heart or lung disease.
Why is the Massachusetts Department of Public Health tracking PM2.5 as a public health issue in the state?
The U.S. Centers for Disease Control and Prevention (CDC) established nationally consistent environmental and health data measures (NCDM) for the environmental and health tracking network. Outdoor air quality NCDMs have been established for two pollutants: PM2.5 and ozone. Linking data on PM2.5concentrations with health data may provide information on the degree to which particle pollution may be contributing to adverse health impacts in communities throughout the state. It will also be useful in tracking the benefits of emission control efforts to reduce particle pollution in the state.
Where does PM2.5 come from?
Major sources of PM2.5 in Massachusetts include industrial process emissions, motor vehicles, incinerators, and power plants.
Who is likely to be affected by exposure to PM2.5, and why?
Older adults, individuals with heart or lung diseases, and children are more likely to be affected by PM2.5 exposure. People with heart and lung diseases are at increased risk because particles can aggravate these diseases. Older adults are at increased risk because they may have undiagnosed lung or heart disease. Children are likely at increased risk because they are still developing and spend more time outdoors and generally at high activity levels.
How can I reduce my exposure to PM2.5?
The Massachusetts Department of Environmental Protection (MassDEP) provides an air quality forecast on a daily basis to inform you when particle levels are expected to be unhealthy. The air quality forecast is based on U.S. EPA's Air Quality Index, or AQI. A semi-continuous, hourly measurement method for PM2.5 is used for real time reporting of PM2.5 values and to assist in developing daily PM2.5 predictions for the AQI. The AQI has a color-coded scale so that people know when air pollution is expected to reach unhealthy levels in their area. The AQI may be used to plan daily activities such as avoiding strenuous activity and shortening time spent outdoors when PM2.5 levels are forecasted to be at the highest.
How is attainment of the PM2.5 National Ambient Air Quality Standard determined using monitoring data?
The federal Clean Air Act (CAA) established timeframes and milestones for states to meet and maintain National Ambient Air Quality Standards (NAAQS) for criteria pollutants. U.S. EPA sets the NAAQS levels to protect public health and the environment. Each state, including Massachusetts, is required to monitor the ambient air to determine whether it meets each standard. Each monitoring site with Federal Reference Method (FRM) monitors is required to achieve 75% or greater data capture for the year in order for the data from the monitoring site to be considered valid in the attainment demonstration. The annual standard is met when the annual average of the quarterly mean PM2.5 concentrations is less than or equal to 12 µg/m3 (3-year average). If spatial averaging is used, the annual average from all monitors within the county may be averaged in the calculation of the 3-year mean. The 24-hour standard is met when the 98th percentile value is less than or equal to 35 µg/m3 (3-year average). If the air quality does not meet a standard, the state must develop and implement pollution control strategies to attain that standard. Once air quality meets a standard, a state must develop a plan to maintain that standard while accounting for future economic and emissions growth. Taken together, these plans and control strategies constitute the State Implementation Plan (SIP). For more: Massachusetts SIP
Are there differences between the calculations for determining NAAQS attainment and determining the EPHT outdoor air quality measures for PM2.5??
Yes. The calculation for the EPHT outdoor air quality measures for PM2.5 are based on the exceedances of daily or annual PM2.5 NAAQS in a county over a one year period whereas the calculation for determining NAAQS attainment is based on the 3-year annual average of the quarterly mean PM2.5 concentrations or a 98th percentile value for the daily PM2.5 NAAQS over a three year period. The outdoor air quality measures are based on monitoring data submitted by the MassDEP to U.S. EPA's Air Quality System, or AQS (http://www.epa.gov/ttn/airs/airsaqs/). EPHT data may also include outdoor air quality monitoring results during "exceptional events", whereas the U.S. EPA allows states to exclude certain "exceptional events" when assessing NAAQS attainment. Exceptional events may include chemical spills and industrial accidents, structural fires, and natural events (volcanoes and earthquakes, high wind events, wildfires). For example, data for several 2002 PM2.5 exceedances was flagged as an "exceptional event,” because they were caused by emissions from a forest fire which occurred in early July of that year in Quebec.
How is the maximum daily and annual average PM2.5 concentration calculated?
The maximum PM2.5 daily concentration is determined by retaining the maximum concentration reported for each monitoring site for each monitored day (i.e. if valid 24-hour averages are available for at least 75% of possible hours in a day). For the annual PM2.5 concentration, a complete (valid) quarterly average must have at least 11 observations (11 valid 24-hour values). For each valid quarter, a quarterly average is calculated. The annual average for each monitor is the average of four valid quarterly averages. The PM2.5 annual average measure is the maximum annual average among monitors with complete (4 valid quarters) data in that county. The values that exceed the NAAQS (i.e., 12.5 µg/m3 and higher for annual average or 35.5 µg/m3 and higher for daily average) are considered above the NAAQS.
How is the number of percent of population and person-days calculated?
The outdoor air quality measures takes into account both the number of days that the maximum daily PM2.5 concentrations exceed the NAAQS and the population within the county where monitors are located. The maximum daily and annual PM2.5 concentrations are calculated based on the methodology presented above. The number of persons in each county is derived from the Census Bureau population estimates. The Census Bureau typically updates the county-level population estimates for the years between censuses on an annual basis. The census county-level population is adjusted annually by considering births, deaths, immigration and other information sources. Documentation on the methodology used by the Census Bureau in estimating county-level can be found in this PDF.
What is modeled outdoor air quality data?
Modeled data are estimates of PM2.5 data generated by a model called Downscaler, which was jointly developed by EPA and CDC. Downscaler uses a statistical approach to combine data collected from air monitoring stations with the statistical output from Community Multiscale Air Quality (CMAQ) model estimates. For additional information about Downscaler and CMAQ, refer to EPA documents on these topics found here.
How is modeled outdoor air quality data used?
In areas where outdoor air monitors are not present, the value reported is the modeled estimate. The Downscaler output provides estimated daily measurements of PM2.5 on days when monitoring data isn’t collected or in locations where monitors are not available.
What limitations of the outdoor air quality measures for ozone need to be considered?
There are several limitations associated with the EPHT PM2.5 outdoor air quality measures that need to be considered:
- The relationship between ambient concentrations and personal exposure is difficult to estimate and varies depending upon pollutant, activity patterns, and microenvironments.
- The percent of days that exceed the U.S. EPA NAAQS or other health benchmarks does not provide information regarding the severity (maximum concentrations) of potential exposures. The data for this measure only represent counties that have air monitors and tend to reflect urban outdoor air quality (where most people live). Thus, although populations in areas without monitors may also be exposed to PM2.5 that exceed the standard, they are not counted.
- Outdoor air quality monitoring data may not coincide with health outcome data because of differences (time, space, or other) between the measurement and the exposure or the lag time between the exposure and the symptoms.
- Person-day estimates for larger, highly populated counties may be biased higher than estimates for smaller less populated counties. The measure uses the highest value of all monitors in the county, so larger counties with more monitors may have a broader range of pollution values and greater potential to measure a high day then smaller counties with fewer monitors.
- The percent of the state's population living in counties with no PM2.5 measurements must always be considered when attempting to estimate the proportion of population at risk.
- The model predictions are used to fill-in air quality estimates in areas and at times without monitoring data. For counties without monitoring data, temporal (seasonal) and spatial (regional) biases in the modeled estimates can influence the accuracy of the measures.
- Modeled outdoor air quality estimates should not be used for NAAQS compliance determination.
Available data on Ozone
Use the Explore Maps & Tables link on this page to access the following measures for outdoor air quality for your community:
- Monitored Ozone (O3), and Particulate Matter (PM2.5) – county only
- Modeled Ozone (O3), and Particulate Matter (PM2.5) – county, community, census tract
- Combined monitored and modeled Ozone (O3), and Particulate Matter (PM2.5) – county only
The most current available data will be shown. Be sure to check the site periodically as new data are added each year.
Where can I get additional information on fine particles?
The following websites offer information on fine particles:
- Information on particulate matter in Massachusetts: MassDEP Particulate Matter FAQ
- Current PM2.5 levels and health implications in Massachusetts: MassAir Online at MassDEP
- Information on outdoor air quality standards for PM2.5: US EPA "Air Quality Criteria for Particulate Matter"
- Information on particulate matter: US EPA Particulate Matter Web Site