WHAT DO WE MEASURE?
Measuring
Air Quality
Measuring Air Quality
Have you ever been outside and found that it was hard to breathe? You might have seen or even smelled smoke. Air pollution is a serious health risk. The Healthy Air Network collects data and informs the public about the current air quality. With this information, people can take steps to protect their health. Observing patterns over time helps us identify the sources of poor air quality and take action to prevent it.
What We Measure
Each circle on the map represents a PurpleAir sensor installed for the Healthy Air Network in communities across the state. Each sensor measures fine particle pollution PM2.5 levels, which are translated to Air Quality Index (AQI) readings.
What is AQI?
The AQI is the EPA’s national index of air pollution and provides information on how to avoid the health effects of poor air quality.
AQI values range from 0 to 500 and are grouped into six color-coded categories: Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, and Hazardous. The color of each sensor on the map reflects its current AQI level and can help you decide whether you need to take steps to protect your health when air quality is poor.
Sensor Card Information & History
In addition to air quality, each sensor card includes wind, weather and pollen information. For people with respiratory illness, the pollen count and temperature can also impact health. In addition, the changing climate is leading to increasing pollen counts and a longer pollen season as well as more days over 90 degrees.
The Sensor Card also shows PM 2.5 measurements over the last 24 hours. In addition you can click on the “View History” link to find past data for specific timeline. You can also change the dates to find specific time periods for air quality information.
Sensors that are not reporting show up as gray on the map. This can be due to a temporary wifi or power outage, or other maintenance issue. We do our best to maintain sensors with the help of our partners. Please contact us if you have questions about a sensor that is offline.
Air Pollution: Understanding what's in the air we breathe
Particles of pollution in the air are very small – many times smaller than a human hair. Sometimes, you can see these small particles – think about smoke from the tailpipe of a car, a burning furnace, a wood fire or haze from wildfire. If we can see them, it means there are high levels of particles. These particles are very small, which allowed them to stay in the air for long periods of time, sometimes hours or even weeks. These tiny particles can travel deep into our lungs which can make it difficult to breathe. Exposure can cause health problems like lung disease, heart disease and COPD.
Particulate Matter
Healthy Air Network sensors measure particles that are very small, less than 1.5 micrometers. Another name for this size of particulate matter is known as fine particulate matter or PM2.5. Their small size lets these particles stay suspended in the air for an extended period of time, and also makes it more likely that we will breathe them into our lungs. PM2.5 is made up of many different chemicals that may be released from many sources like vehicles, factories, and wildfires. High levels of PM2.5 in the air can reduce visibility and impact our health.
Learn more about particulate pollution:
- American Lung Association, What Makes Air Unhealthy
- EPA, Particulate Matter Basics
Ozone
Ozone is a gas that can be good or bad depending on where it is.
- Ozone is a gas that can be good or bad depending on where it is.
- Ozone at ground level can react with sunlight and other air pollutants to form smog. This is harmful for health. Ozone itself is a strong oxidant which can be harmful to our health.
Learn more about ozone:
- American Lung Association, Ozone
- CDC, Air pollutants
- EPA, Ground level ozone pollution
Air Pollution Sources
Pollution can come from different sources:
- Transportation: cars, trucks, buses, planes and any other vehicle that burns gas or diesel fuel
- Heating: Furnaces or stoves that burn gas, wood or oil
- Factories and power plants: Gas, coal, and other fuels are burned to create energy and products
- Wildfires: Wildfire smoke can have an impact far from the site of the fires themselves. Wildfires are increasing due to climate change, land use and fire management practices.
Learn more on sources of air pollution:
How We Measure Air Quality
Differences between platforms
How researchers measure air pollution, and how they use these values to calculate the AQI makes a big difference in the AQI each data source reports. The Healthy Air Network Coalition, which measures air quality for the Air Watch app, is focused on creating actionable and accurate information to share with the public for current decision making. This focus has led the Healthy Air Network to make the following decisions regarding how we measure local PM2.5 and use that value to calculate AQI:
- We require all PM2.5 sensors (PurpleAir sensors) to be calibrated to standard EPA reference sensors to improve accuracy.
- We share 1-hour rolling average PM2.5 mass concentrations to show timely data.
- Similarly, we share 1-hour rolling average AQI values based on our measured PM2.5 mass concentration measurements.
These methods differ in some key ways from other air quality platforms, such as Purple Air, AirNow, and Mass DEP. This can cause other platforms to show values that look noticeably different, which may be confusing.
PurpleAir Real-Time Map
The default settings of the PurpleAir Real-time Map sometimes show higher PM2.5 and AQI values than the Healthy Air Network. Some reasons for this are:
- The PurpleAir Real-time map defaults to showing uncalibrated sensor values. This makes PurpleAir PM2.5 (and the resulting AQI) values appear to be higher than is accurate (especially for wildfire smoke which requires a high adjustment factor to increase accuracy compared to federal reference method monitors). To view more accurate PM2.5 mass concentrations during wildfire smoke periods, we recommend applying the “woodsmoke” conversion factor on the Purple Air map.
- The Purple Air map defaults to showing air quality information with a 10-minute averaging period. Air quality can at times change rapidly, and this can make the values look different than the Healthy Air Network’s values which are averaged over an hour, as opposed to 10 minutes.
AirNow & MassDEP
The AirNow and Massachusetts Department of Environmental Protection websites can also show higher AQI values than the Healthy Air Network. One reason for this is that the AirNow platform uses the regulatory approach to calculate AQI, which calculates AQI using PM2.5 values measured over the past 24 hours, not just one hour.
Examples from 7/15/2026 Wildfire Smoke Event
MassDEP 1:04 PM
24 hour average sensor readings
PurpleAir 1:06 PM
Uncalibrated PurpleAir sensors
Healthy Air Network 1:05 PM
1 hour calibrated readings
Calibration
Before installing the sensors in communities, the sensors are sent to our team at Yale School of Public Health for calibration. The sensors are placed placed for a minimum of two weeks at an EPA monitoring station to collocate with regulatory grade reference air monitors. The Yale team then applies that calibration to the sensor readings once they are deployed. Once sensors are installed at network sites, the operating status of these sensors are continuously monitored in real-time through an online sensor health dashboard.
Although Purple Air sensors tend to give pretty consistent readings, they can vary from each other by as much as 20-30%. By calibrating sensors individually we can account for these variations to report more accurate data on the Healthy Air website.
Note that websites such as Purple Air and Air Now have an option to apply a universal calibration factor to the raw readings. This helps to make the data more accurate, but not as accurate as the individual calibrations provided by Yale.
Sensor Data Analysis
Air Quality Changes Throughout the Day
There are many sources around us that release pollutants into the air. Major sources of air pollution in Springfield, Chicopee, and Holyoke are gas and diesel vehicles. Morning and afternoon rush hour on the extensive network of interstate highways in this area lead to changes in air quality over the course of a day.
There are many sources around us that release pollutants into the air. Major sources of air pollution in Springfield, Chicopee, and Holyoke are gas and diesel vehicles. Morning and afternoon rush hour on the extensive network of interstate highways in this area lead to changes in air quality over the course of a day.
When we look at fine particulate matter (PM2.5) measured across 2022 and 2024 at locations across the Healthy Air Network in Springfield, Chicopee, and Holyoke, we see the highest levels around 8 am. More vehicles on the road commonly causes the air quality index (AQI) to be ‘moderate’. This level of air quality is considered to be acceptable by the US Environmental Protection Agency (EPA), but some people may experience health concerns. The symptoms of people with asthma or other respiratory conditions may worsen when the air quality is moderate.
In the middle of the day, the number of vehicles on the road go down and air quality across the region typically improves. The air quality index midday in the Springfield, Chicopee, and Holyoke is commonly considered to be ‘good’. This means the air quality is poses little to no risk.
As more people get back in the vehicles at the end of day to head home, PM2.5 levels usually rise. Air pollutants released from cars and trucks during afternoon rush hour cause the AQI to be ‘moderate’.
To keep our air as healthy as possible, try to avoid using your vehicle. If possible, consider walking, riding a bike, or taking public transportation.
Air Quality is Different Depending Where You are
Air quality can be different in one community compared to another. For example, levels of fine particulate matter (PM2.5) vary from one side of the Connecticut River to the other in Longmeadow and Agawam.
Using air sensors installed at multiple locations in Holyoke, Chicopee, and Springfield, we looked at PM2.5 concentrations measured between 2022 and 2024 to explore how your exposure to air pollution can vary across this region. Map were created of PM2.5 levels across Holyoke, Chicopee, and Springfield. Low levels are shown in green, moderate levels are marked in orange, and high levels are colored in pink and white. Air pollution tended to be worse in areas with lots of gas and diesel vehicle traffic. Communities including Pine Point, Boston Road, Upper Hill in Springfield and Aldenville and Chicopee Falls in Chicopee had a higher PM2.5 levels than other areas.
Air sensors operated by the Healthy Air Network measure PM2.5 levels every 2 minutes, 7 days a week, 24 hours a day. All of these measurement taken through the day, showed that air quality changed from one hour to the next. The communities in Springfield and Chicopee that high PM2.5 only had high levels for parts of the days. Parts of Chicopee had a poor air quality during morning and evening rush hours while Pine Point, Boston Road, Upper Hill in Springfield had higher PM2.5 levels later at night (9-11pm).
You can make a difference to improve community’s air quality! Instead taking a car, consider walking, biking or taking the bus. Getting gas and diesel vehicles off the road, will help make our air healthier.
Air Quality Changes by Season
The air quality in our communities is constantly changing. We explored fine particulate matter (PM2.5) mass concentration measurements that were made through air sensor operated by the Healthy Air Network. Measurements of outdoor air quality are made every 2 minutes, 7 days a week, 24 hours a day.
By looking at measurements made between 2022 and 2024, we found that during the spring and fall months, outdoor air quality is typically good. This means the air quality is poses little to no risk to our health.
Levels of PM2.5 tended to be higher in the summer and winter months. The poor air quality during these times of the year are mostly because of PM2.5 released from wildfires in the summer and homes using wood furnaces in the winter. The air quality index (AQI) during July to August and January to February are considered to be ‘moderate’ by the US Environmental Protection Agency (EPA). While a moderate AQI is acceptable for most people. Some people with asthma or other respiratory conditions may have worse symptoms during these time.
If you experience symptoms during time with poorer air quality, avoid intense physical activities outside.
Traffic Impacts Local Air Quality
The Healthy Air Network operated over 100 air sensors across Massachusetts. To explore the influence of traffic, we looked at sensors in the western Massachusetts that most frequently measured the highest and the lowest PM2.5 mass concentrations over the past year.
We found that sensors located in downtown Springfield and Greenfield most frequently had the highest levels of PM2.5. The location of this air sensors are shown with red markers on the map. Sensors in Westfield, East Longmeadow and other smaller communities most frequently had the lowest levels in this part of the state and are shown with blue markers on the map.
While some locations had higher poorer air quality, levels are below the EPA National Ambient Air Quality Standard for PM2.5 set at 35 µg/m3.
We looked at how the PM2.5 mass concentrations measured at these locations changed across each hour of the day for different months of the year. The variation in air quality levels are shown in red for the location that most frequently had higher PM2.5 levels and in blue for the sensor sites that most frequently had lower PM2.5 levels.
The locations with air sensors that consistently measured lower levels of PM2.5 had very little variation in air quality. Concentrations ranged from about 6 to 10 µg/m3, regardless of time of day or the month. Some higher levels were seen in the summer which may have been from wildfires.
The locations with air sensors that consistently measured higher levels of PM2.5 had more variation in air quality across the day and across seasons. Concentrations typically ranged from 8 to 16 µg/m3 . There were cases of higher levels in the summer that were likely because of wildfires. When you look at the PM2.5 concentrations measured across the day, there were some common patterns across all these air monitoring sites. During the fall and winter, concentrations rise during morning rush hour from about 6 to 10 AM. Levels then drop in the middle of the day, go up again around the afternoon rush hour, and stay high overnight.
The drop in PM2.5 levels midday commonly happens in towns and cities across the US. It is typically caused by air mixing that happens when the ground is warmed by the sun. Warming the ground also heats the air above it. This warm air rises and mixes with the cooler air above. More air mixing gives PM2.5 more space to spread out which lowers concentrations.
The rise in PM2.5 levels overnight can happen because there is less air mixing. Pollutants in the air get trapped near the ground as the ground and air above it cools down.
Air Quality between 2022-2024
The Healthy Air Network has operated air sensors across Western Massachusetts since summer of 2022. These air sensors have been continuously measuring levels of fine particulate matter (PM2.5) mass 7 days a week, 24 hours a day!
We looked at the air quality across our communities over between 2022-2025 to see how PM2.5 changed month to month.
For most of this time, air quality was good! This means that the levels of PM2.5 were low and posed little to no risk to our health.
There were times when we had poorer outdoor air quality. Over the summers of 2023 and 2024, PM2.5 levels tended to be higher. This was because of wildfires that were actively burning in other areas. There were also higher PM2.5 levels between December 2023 and February 2024. Poor air quality over these winter mouths was likely impacted by homes burning wood in their furnaces. During these times, air quality index (AQI) was classified as ‘moderate’ by the US Environmental Protection Agency (EPA). While a moderate AQI is acceptable for most people. Some people with asthma or other respiratory conditions may have worse symptoms during these time.
Data Sharing
Yale University School of Public Health has a database of air sensor data collected for the Healthy Air Network. Nonprofit organizations and researchers can request samples/data by completing a proposal describing their proposed work. The Healthy Air Network Data Committee will review each proposal and grant access based on the merits of the application. Applicants then pay for data access and are required to report analysis outcomes/publications annually.
Sensor Installation & Troubleshooting
Hosting a Sensor
The Healthy Air Network works though our partners to find hosts for the air sensors.
The air sensors require:
- Access to an outdoor power outlet to plug in the sensor
- Access to WiFi within the range of the power outlet
The sensor should be sited:
- Within 6 ft of a power outlet
- Within 100 feet of the Wi-Fi router
- At least 6 ft above ground, avoiding exhaust or vents
- On a flat surface which can accommodate screws for mounting
- In a protected location, like an eave
- In an accessible location for potential maintenance
- In an area clear from other structures or devices
Already have a Purple Air Sensor?
If you or your organization already has a sensor(s), we can work with you to add your sensor to our network. All sensors must be calibrated by Yale School of Public Health to ensure the best quality data for the network. This means that the sensor must taken down and shipped to the Yale team for calibration.
Detailed information on installation and connection
Troubleshooting Sensors
We are setting up an automated email alert for sensors that stop reporting after 12 hours. In the meantime, our team checks on air sensors. We ask our sensor hosts to do the same. In the event of the sensor outage – when it turns gray on the map– please follow these steps:
1. Check the power
Unplug the unit at the power outlet, wait 10 seconds, and plug it back in. This power reset usually fixes the connection!
It can take up to an hour for the sensor to show up as a colored dot again on the Healthy Air Network map.
2. Check on the WiFi
Have you recently updated the Wi-Fi information or password?
- If the Wi-Fi password or network has not changed and the sensor loses power, the sensor will automatically reconnect to the network. The sensor saves the Wi-Fi password. Be patient with the reconnection.
- If the Wi-Fi password or network has changed, the sensor will need to be manually reconnected to the internet using your phone. Go outside and stand by the air sensor to connect to the sensor using your phone.
For Purple Air Sensors
Look at your list of available Wi-Fi networks and select the “AirMonitor_xxx” code for your sensor from the drop-down. This will direct you to the PurpleAir Website, where you can input your updated Wi-Fi information and get the sensor back online
For AirU Sensors
For AirU Sensors – Open the Tetrad Connect App and press “Provision Device.” Using your phone Bluetooth, you will be able to connect to the AirU sensor and input the updated Wi-Fi information and password to reconnect.
3. Check for damage or missing parts
Sometime spiders or other creatures try to make a home in the sensors. Please check to see if any debris or cobwebs are limiting sensor function. If there is any distinct damage or missing parts, such as a lost or broken power cable, we will do our best to replace it, based on available funding.
4. Contact us
If problems persist, contact us or your regional partner.
Healthy Air Network
Healthy Air Network
The Healthy Air Network is a collaboration of organizations and community members who work to improve air quality, increase climate resilience, and advocate for environmental justice in Massachusetts. Convened by the Public Health Institute of Western Massachusetts
