Technical Approaches for the Sensor Data on the AirNow Fire and Smoke Map

EPA and the U.S. Forest Service (USFS) are conducting the AirNow Sensor Data Pilot to show data from air sensors on the Fire and Smoke Map, located on the AirNow.gov website.

The goal of the pilot, launched in August 2020, is to provide people with additional information on air quality during wildfires, especially in areas where AirNow monitors may not exist. The Fire and Smoke Map includes data from:

Sensor data from PurpleAir, a company that offers publicly available crowdsourced fine particulate matter (PM2.5) data from an international network.
Stationary long-term monitoring stations that are used to report outdoor air quality to the public on AirNow.gov. These are generally operated by state, local or tribal air quality agencies and stay in place for many years.
Temporary monitors that agencies use to monitor smoke events.

The map also provides information on large fire incidents, satellite-detected fires, smoke plumes, and special smoke statements.

The sensor data incorporated onto the map during this initial pilot, is fine particulate matter (PM_2.5) data from PurpleAir sensors. Fine particulate matter is an air pollutant that can impact the lungs and heart and cause adverse health effects. Out-of-the-box, data from these air sensors are not comparable to data from regulatory-grade monitors. In order to make the data more comparable to other data sources on this map, EPA developed a series of quality control checks and an extended U.S.-wide correction equation which is applied to the data before it is displayed on the Fire and Smoke Map. These steps make it easier for users to compare sensor data and permanent and temporary monitor data side by side.

EPA and the USFS plan to continually improve the sensor data map layer.

Below is a series of video segments from three webinars given throughout spring 2021. The videos providing detailed information on key features of the Fire and Smoke map, how it compares to other data sources, and how the air sensor data is processed and presented using the extended U.S.-wide correction. NOTE: We are in the process of updating these videos to reflect the newest changes to the correction equation. The most up to date correction can be found on slide 26 of Sensor Data Cleaning and Correction: Application on the AirNow Fire and Smoke Map. Some screenshots in the videos may be from previous versions of the map.

This material aims to give map users, air quality managers, and other technical audiences information about EPA’s research so that they can have confidence in the use of the fire and smoke map and the extended U.S.-wide correction equation for PurpleAir PM_2.5 data during normal ambient conditions and smoke impacted times.

AirNow Sensor Data Pilot Video [27 minutes] In this webinar segment Dr. Sim Larkin, US Forest Service, walks through the data layers available on the Fire and Smoke map and some of the challenges with integrating the different data streams. The webinar segment includes an overview of map updates for 2021.

PurpleAir Sensors and Comparison Between Air Quality Maps [18 minutes] In this segment Dr. Andrea Clements, US EPA Office of Research and Development, gives an introduction to the PurpleAir sensor in use on the AirNow Fire and Smoke map. She also discusses how the Fire and Smoke map compares to both the AirNow map and the PurpleAir map.

Key Considerations about PurpleAir Sensors and Crowdsourced Data [6 minutes] In this segment Dr. Andrea Clements, US EPA Office of Research and Development, discusses limitations of PurpleAir crowdsourced data including the unknown location of sensors, limitations on sizes of particles measured, and potential issues with sensor placement.

Sensor Users Frequently Asked Questions [5 minutes] In this segment Dr. Amara Holder, US EPA Office of Research and Development, discusses why a sensor may not show up on the fire and smoke map, how to properly site your air sensor, and what would be needed to have similar confidence in other air sensor types.

Updating the U.S.-wide PM_2.5Correction for PurpleAir Sensors [8 minutes] In this segment Dr. Karoline Barkjohn, US EPA Office of Research and Development, discusses building an updated U.S.-wide correction with an extended range up to 1500 µg m^-3. She also discusses how the correction compares to other corrections currently available on the PurpleAir map.

Additional Webinars and Related Publications

EPA does not endorse any particular commercial product. Mention of trade names or commercial products does not constitute EPA or USFS endorsement or recommendation for use.

Related Resources

AirNow
Fire and Smoke Map (FAQ on the map and sensor data are available by clicking on the “FAQ” icon on the top right of the map)
Using AirNow During Wildfires
Science Matters Newsletter article on research to improve accuracies of air sensors
Particulate matter basics

Contacts

For inquiries regarding the Fire and Smoke Map: firesmokemap@epa.gov