MA EPHT - Fine Particles (PM2.5)

PM2.5 are tiny particles in the air we breathe which can deposit deep in our lungs and have been linked to lung disease, cardiovascular disease, and cancer. The Massachusetts Environmental Public Health Tracking (MA EPHT) Program provides data on PM2.5 statewide.

Explore outdoor air quality data 

What is PM_2.5?

Particulate matter (PM) is a complex mixture of extremely small solid particles and liquid droplets in the air. It can be made of acids, organic chemicals, metals, soil, dust, or allergens like fragments of pollen or mold spores.

Particulate matter is grouped into three categories by size: PM₁₀, PM_2.5, and ultrafine particles. The size of the particles is directly linked to their potential to cause health problems. Particles less than 10 micrometers in diameter pose the greatest risk. These particles can pass through the nose and throat and enter the lungs. PM_2.5 are also known as fine particles. These particles are 2.5 micrometers in diameter or smaller. 

Why does MA EPHT track PM_2.5? 

Fine particles can deposit deep into the lungs and increase the risk of developing respiratory and cardiovascular conditions. Tracking levels of PM_2.5 over time alongside health data can help us better understand the impact of particle pollution on health. It can also be used to identify communities that may have an elevated risk of exposure and track the benefits of emission control efforts to reduce pollution.

MA EPHT tracks PM_2.5 with both monitored and modeled data. The EPA and the U.S. Centers for Disease Control and Prevention (CDC) use the downscaler model to combine measurements from the EPA's Air Quality System (AQS) with predictions from the Community Multi-Scale Air Quality Model (CMAQ). These data fill in the gaps that exist in the monitored data.

In counties with monitors, the combined “monitored and modeled” pollutant dataset is used to look at pollution trends at the local and community levels. The combination of monitored and modeled data allows us to look at the frequency of poor air quality events and historical trends. This understanding can inform future estimates and forecasts of air quality conditions.   

How can PM_2.5 affect my health? 

PM_2.5 is linked with increased respiratory and cardiovascular symptoms. These include irritation of the airways, coughing, or difficulty breathing. It can also lead to decreased lung function. 

Short-term exposure over hours or days can aggravate pre-existing conditions. This can lead to asthma attacks, acute bronchitis, or respiratory infections. In people with heart disease, PM_2.5 has been linked with irregular heartbeat and heart attack. While healthy children and adults have not been reported to suffer serious effects from short-term exposures, they may experience temporary minor irritation like coughing or eye irritation when particle levels are elevated.

Long-term exposure to high levels of PM_2.5 over many years is associated with serious health impacts, such as reduced lung function, chronic bronchitis, and lung cancer. It can also lead to premature death.

Those most susceptible to the effects of PM_2.5 include:

• Older adults age 65 and over
• People with pre-existing medical conditions such as heart disease or lung disease
• Children
• People who are physically active outdoors

Older adults over age 65 are more likely to have pre-existing medical conditions or undiagnosed lung or heart disease. Children are still developing, spend more time outdoors, and generally are more active. All these factors influence risk.   

How can I be exposed to PM_2.5? 

Major sources of PM_2.5 in Massachusetts include emissions from industrial processes, motor vehicles, incinerators, and power plants. PM_2.5 are also generated from residential wood burning, road dust, and fossil fuel combustion. Statewide levels can also be affected by the transport of PM_2.5 from out-of-state sources. For example, particles from forest fires can travel long distances upwind. PM_2.5 may reach extreme levels during wildfire smoke events and summertime heat waves.

Once in the air around us, PM_2.5 can be breathed in. Due to its size, it can penetrate deep into the lungs. Those who are physically active may be at a greater risk of exposure. Exercise and physical activity cause people to breathe faster and more deeply - taking more particles into their lungs. There are many health studies that link exposure to PM_2.5 in the ambient air with adverse health outcomes. 

Fine particles (PM2.5) are the main cause of reduced visibility (haze) in parts of the United States.

How can I prevent exposure to PM_2.5? 

The Massachusetts Department of Environmental Protection (MassDEP) provides a daily air quality forecast to warn when particle levels are expected to be unhealthy. A semi-continuous, hourly measurement method for PM_2.5 is used for real time reporting and to develop daily PM_2.5 predictions. The air quality forecast is based on U.S. EPA's Air Quality Index (AQI).

The AQI has a color-coded scale and is used to let people know when air pollution is expected to reach unhealthy levels in their area. The AQI can be used to plan daily activities. For example, if the AQI is high, you may want to avoid strenuous activity outside or shorten your time spent outdoors. 

What are the air quality standards for PM_2.5? 

Outdoor air quality regulations currently exist for PM₁₀ and PM_2.5. These are established by the federal Clean Air Act (CAA), which sets timeframes and milestones for states to meet and maintain air quality standards. These standards are called the National Ambient Air Quality Standards (NAAQS). EPA sets the NAAQS levels to protect public health and the environment. 

The NAAQS have annual and 24-hour standards for PM_2.5. The annual standard for PM_2.5 is 9 µg/m³. The annual standard is satisfied if the quarterly mean PM_2.5 concentrations, taken over a 3-year period, is less than or equal to the standard. 

The 24-hour standard is 35 µg/m³. The 24-hour standard is satisfied if the 98th percentile value of the PM_2.5 concentration, taken over a 3-year period, is less than or equal to the standard. 

If air quality does not meet the standards, the state must develop pollution control strategies. Once air quality meets a standard, the 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 Plans (SIPs). For more information, see the Massachusetts SIP. 

What are the monitoring requirements for PM_2.5? 

Each state is required to monitor the ambient air to determine if it meets the NAAQS. EPA determines the minimum number of monitors required in an area based on the population size and the expected air quality status. One site must be located where the highest PM_2.5 concentration is expected. An additional monitor must be located at a near-road site for areas with a population of at least 1 million people. A third monitor is required for some areas of poor air quality where communities are at higher risk of health effects. For more information, see EPA’s fact sheet on air monitoring for fine particle pollution (PM_2.5). 

Available data

Use the Explore outdoor air quality data link on this page to access the following measures for PM_2.5 modeled, monitored, and combined monitored and modeled data:

• Number of person-days over the NAAQS
• Percent of days over the NAAQS
• Number of days over the NAAQS
• Annual average concentration

Number of person-days over the NAAQS is a measure used to estimate exposure. It accounts for the number of days that the maximum daily PM_2.5 concentrations exceed the NAAQS and the population within the county where monitors are located. The calculation for the EPHT outdoor air quality measures for PM_2.5 are based on the exceedances of daily or annual PM_2.5 NAAQS over a one-year period.

The PM_2.5 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., 9.0 µg/m³ and higher for annual average or 35.5 µg/m³ and higher for daily average) are considered above the NAAQS.

Combined and monitored data are available at the county level only. Modeled PM_2.5 data is available at the county, community, and census tract levels. The most current available data will be shown. Be sure to check the site periodically as new data are added.  

Related links

Outdoor air quality  Ground-level ozone 

Additional resources

Massachusetts 

• MassDEP MassAir Online: Current PM_2.5 levels and information for Massachusetts
• Massachusetts State Implementation Plans (SIPs): Information on how Massachusetts ensures that it meets the NAAQS and regional haze goals under the Clean Air Act
• DPH fact sheets on poor outdoor air quality: Learn about climate and poor outdoor quality. Available in 16 languages

National 

• EPA - Particulate matter (PM) pollution: Information on particulate matter and how PM standards are set and implemented
• EPA Air Quality System (AQS): EPA's repository of ambient air quality data that assists in air quality assessments, designations, modeling for permit review, and preparing reports as mandated by the Clean Air Act
• EPA Community Multiscale Air Quality (CMAQ) modeling system: Active open-source development project of the U.S. EPA that consists of a suite of programs for conducting air quality model simulations
• EPA’s fact sheet on air monitoring for fine particle pollution (PM_2.5):  Summary of changes to the NAAQS in 2024 and overview of PM_2.5 monitoring