The Fire and Smoke Map displays information on ground level air quality monitors recording fine particulates (PM2.5) from smoke and other sources, as well as information on fires, smoke plume locations, and special statements about smoke issued by various sources.
This map is designed to:
A note about the Fire and Smoke Map:
U.S. EPA and U.S. Forest Service are conducting a pilot project to add data from air sensors to the Fire and Smoke Map. The data appear as a map layer called Low-Cost Sensors that users can turn off or on as needed. Sensor technology provides thousands of additional particle pollution data points that can be used to supplement the air monitoring stations operated by official air agencies. The sensor data undergoes QA screening, is averaged to hourly values, is corrected for bias, and has the EPA NowCast algorithm applied. This means that the sensor data can use the AQI color scale when it appears alongside the monitoring data that is already on the AirNow Fire and Smoke map. Sensor data is informational only. It will not be used for regulatory purposes.
This map is a collaborative effort between the U.S. Forest Service led Interagency Wildland Fire Air Quality Response Program (IWFAQRP) and the U.S. Environmental Protection Agency. Development work was done through an agreement with the University of Washington’s School of Environmental and Forest Sciences. This site relies on data provided from a number of sources.
Project Lead: Sim Larkin, USFS
Lead Developer: Stuart Illson, University of Washington
Additional Development: Jonathan Callahan, Mazama Science; Joel Dubowy, University of Washington; Chris Wilkes, EPA
Steering Group:EPA: Phil Dickerson, Ron Evans, Lourdes Morales, Susan Stone, Alison Davis, Lori Tussey, Michelle Wayland, John E. White, Rob Wildermann; USFS: Pete Lahm
User Guide: Gina Wing, USFS; Marlin Martinez, University of Washington
EPA and USFS are continuing to pilot improvements to the map as we work toward our joint goal of sharing actionable information about wildfire smoke with the public. We welcome your feedback. Email us at firesmokemap@epa.gov.
Air quality (PM2.5) information from official monitors is shown as circles, air quality (PM2.5) information from temporary monitors placed by agencies during smoke events is shown as triangles, air quality (PM2.5) information from low-cost sensors is shown as squares, large fire incidents as fire icons, satellite fire detections as small glowing points, and smoke plume locations as grey polygons. The location currently set is shown as a flashing blue circle.
Please Note:
Top Menu
Local Conditions Icons
Shows information about the currently set location of interest. Clicking on any of the icons will bring out the Location Condition Sidebar.
Refresh
Zoom
Map layers can be selected on the Map Layer Control in the Top Menu in the upper left of the map.
Air Quality (PM2.5) Layers:
Monitors and sensors reporting PM2.5 data can be turned off or on (all are on by default). Separate controls are given for:
Fire Information Layers:
Smoke Plume Layers:
Smoke Plume Layers:
Special Smoke Statements Layers:
Basemaps:
The map will continue to display the data available at the time it was originally loaded. To refresh the data with the latest information press the button in the lower left corner or click on the prompt. Refreshing more frequently than every 15 minutes is generally not recommended.
A pull out sidebar showing conditions will appear when the Location Condition Icons or Location Dot Control are clicked. This sidebar shows the conditions nearby the set location of interest. To change where the location of interest is set click on the Location Dot Control or Search Control in the Top Menu in the upper right, or drag the blue dot on the map to the location of interest. The sidebar shows several different sets of information including air quality (PM2.5) conditions, nearby fires, nearby detected smoke plumes, and any special smoke statements issued for this location.
Air Quality (PM2.5): Fine particulate (PM2.5) air quality conditions are shown for both monitors (permanent and temporary) as well as low-cost sensors nearest the set location of interest. For monitors and sensors within 30 mi, the closest three monitors and sensors are shown. If no monitors are within 30 mi, the nearest monitor is shown. Click on one of the monitors to see the measurements and conditions at that monitor.
Fires: Local fire conditions indicate whether there is presence of a potential fire within a 150 mile radius of the user defined position (either set through geolocation or manually). Large fire incidents and satellite fire detections are shown. False detections have been known to occur. Presence as well as spatial measures such as distance and directionality should not be used for tactical decisions.
Smoke Plumes: Local smoke plume conditions indicate whether there is presence of a satellite detected smoke plume either at the user defined position (either set through geolocation or manually), or within a 150 mile radius. Presence as well as spatial measures such as distance and directionality should not be used for tactical decisions.
Special Smoke Statements: Smoke Outlooks issued by the Interagency Wildland Fire Air Quality Response Program’s Air Resource Advisors that apply to the location of interest will appear here. Click to view the Smoke Outlook.
The Fire and Smoke Map shows fine particulate (<2.5 micron, PM2.5) pollution data obtained from air quality monitors and sensors. Information is shown on both the EPA’s Air Quality Index scale, using the NowCast AQI algorithm, and also as hourly PM2.5 concentration values. For low-cost sensor data, a correction equation is also applied to mitigate bias in the sensor data.
The AQI is EPA’s index for reporting air quality. It tells you how clean or polluted your air is, and what associated health effects might be a concern for you. The AQI can be calculated for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. See more information about the AQI.
The AQI used in the Fire and Smoke Map is specifically focused on fine particulate matter (PM) known as PM2.5. PM stands for particulate matter (also called particle pollution), the term for a mixture of solid particles and liquid droplets found in the air. PM2.5 specifically refers to fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller. See more information about the PM2.5 or the Air Quality Guide for Particle Pollution
It is possible that ozone or PM10 could drive the local AQI in certain circumstances. To see a map that includes ozone and PM10 in addition to PM2.5, please see the AirNow Interactive Map.
NowCast refers to an algorithm that is applied to the hourly permanent, temporary, and sensor data when an estimate of the current hourly AQI is needed. The AQI for PM2.5 is a 24-hour average, so EPA uses an algorithm to estimate the current AQI based on multiple hours of past data. The NowCast uses longer averages during periods of stable air quality and shorter averages when air quality is changing rapidly, such as during a wildfire. However, the NowCast is not designed to react to changes that are shorter than a 3 hr period in duration.
See more information about the NowCast AQI.
PM stands for particulate matter (also called particle pollution), the term for a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope. PM2.5 specifically refers to fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller. See more information about PM2.5 or the Air Quality Guide for Particle Pollution
| Daily AQI Color | Levels of Concern | Values of Index | Description of Air Quality |
|---|---|---|---|
| Green | Good | 0 to 50 | Air quality is satisfactory, and air pollution poses little or no risk. |
| Yellow | Moderate | 51 to 100 | Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution. |
| Orange | Unhealthy for Sensitive Groups | 101 to 150 | Members of sensitive groups may experience health effects. The general public is less likely to be affected. |
| Red | Unhealthy | 151 to 200 | Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects. |
| Purple | Very Unhealthy | 201 to 300 | Health alert: The risk of health effects is increased for everyone. |
| Maroon | Hazardous | 301 and higher | Health warning of emergency conditions: everyone is more likely to be affected. |
Note: Values above 500 are considered Beyond the AQI. Follow recommendations for the Hazardous category. Additional information on reducing exposure to extremely high levels of particle pollution is available here.
Learn More about the AQI, as well as the Air Quality Guide for Particle Pollution, and how to be Smoke Ready, including protective actions for wildland fire smoke.
The map displays 3 types of air quality monitors:
Clicking on any monitor or sensor will bring up a popup box that shows additional information for the unit including its:
The historical timeseries of values is shown for the past 10 days (when viewed on desktop displays) or 3 days (on mobile devices). Hovering over any particular hour on the timeseries shows the value. The user can zoom into a portion of the timeseries by clicking and selecting a section of the timeseries.
Permanent particulate monitors are owned and maintained by various entities, including: federal, state, tribal, and local agencies. These monitors are regulatory-grade, and the data they produce is of the highest quality.
Most monitors report out hourly. Data for permanent monitors is obtained through the EPA AirNow system which aggregates data feeds from a large number of agencies and organizations on an hourly basis. Data lag in transmission to AirNow is dependent on the specific monitor data transmission methodology and agency involved. Data is retrieved from AirNow every 3 min.
Temporary MonitorsTemporary, portable particulate monitors are deployed near large, active wildfires by the US Forest Service and state and local agencies. Most monitors report out hourly.
Data for temporary monitors is obtained through the AirSis and the Western Regional Climate Center (WRCC) data feeds. Data is retrieved approximately every 15min, but the monitors themselves only report hourly aggregates based on the clock hour (e.g. 2-3pm). Further transmission lags, particularly with the GOES satellite transmissions processed by the WRCC can sometimes take several hours.
Low-Cost SensorsLow-Cost Sensors are portable, generally easier to operate than regulatory-grade monitors, and available on the commercial market. Most sensors report out every few minutes. Most sensors report out every few minutes. Most low-cost sensors do not have data quality that is comparable to the monitoring stations operated by air agencies. For the pilot, sensor data have been averaged to an hour, QA screened, corrected for bias, and NowCast.
Data for low cost sensors is currently obtained through the PurpleAir network with potentially other networks added in the future. The PurpleAir data has undergone QA screening.
PurpleAir data is collected every 2 min, but only displayed after aggregating to a calendar hour (e.g. 2-3pm) and processing through the correction factor and NowCast AQI algorithm. This processing can take up to 15 min. Additionally, the processing and time smoothing of the hourly aggregation and NowCast algorithm means that the PurpleAir data shown here will not respond as rapidly as the 10 min averages and other shorter term time averages available on the PurpleAir website. Work is ongoing to investigate best to include shorter term time averages or data updates on this map.
See Section 5. Data Limitations and Disclaimers for important limitations on the data shown.
Two types of fire information are presented on the map: large fire incidents and satellite fire detections.
Large Fire Incident
Active large fire incidents from the U.S. National Interagency Fire Center’s active incident feed are presented as fire icons. Clicking on a fire displays information about the fire. Note that these incidents may not have updated for several days due to the nature of the reporting systems used. Additional information on these incidents is available through the Inciweb system (https://inciweb.nwcg.gov). While the information presented by this feed can be several days old, it does present important management information including the fire name, overall fire size, and containment.
Data is downloaded every 15 min.
Satellite fire detections are based on information from the National Oceanic and Atmospheric Administration’s (NOAA) Hazard Mapping System (HMS). This is a combination of automated satellite detected “hotspots” from various satellites and human analyzed fire locations based on smoke plumes. Hotspot detections are based on higher than normal temperatures visible to the satellite from a location on the ground. This represents the detection of above normal temperatures, and does not necessarily reflect the presence of an actual wildland fire, as false detections have been known to occur. Additionally, depending on the satellite the specific location covered by the image pixel may be 1 or more kilometers in resolution. Additionally geolocation error can occur due to other reasons. For large fires, multiple satellite detections may occur for the same fire.
Data is downloaded every 15 minutes from the NOAA Hazard Mapping System (HMS), but HMS updates can sometimes take a few hours to occur.
Smoke plume locations are based on information from the NOAA Hazard Mapping System based on polygons drawn around smoke detected in satellite imagery. In general this represents the presence of smoke in the overall column of air at those locations. However, it may not correspond to smoke being present at ground level; the smoke could be aloft instead. Additionally it will not represent smaller smoke plumes or smoke plumes otherwise not detected by the satellite images (e.g. due to cloud cover, or because they have occurred after the satellite image was taken).
Data is downloaded every 15 minutes from the NOAA Hazard Mapping System (HMS), but HMS updates can sometimes take a few hours to occur.
Whenever the location of interest is within the area of a Special Smoke Statement, a banner is displayed notifying the user and the Special Smoke Statement section of the Sidebar will also display this information. Clicking the link takes the user to the Special Smoke Statement (or to a list if there is more than one). Currently the map only displays as Special Smoke Statements smoke outlooks produced by deployed U.S. Interagency Wildland Fire Air Quality Response Program Air Resource Advisors, but the inclusion of additional smoke outlooks and forecasts are being investigated. The boundaries of areas with smoke outlooks can be turned on the Map Layer Control.
U.S. Interagency Wildland Fire Air Quality Response Program smoke outlooks are retrieved every 5 min.
EPA and USFS are conducting a pilot project to add data from low-cost sensors to the Fire and Smoke map. While these sensors don’t meet the rigorous standards required for regulatory monitors, they can help you get a picture of air quality nearest you – especially when wildfire smoke is in your area. Use the map layer icon in the upper righthand corner of the map to turn on information from AirNow monitors, USFS temporary monitors, and sensors. EPA and USFS may update the sensor map layer several times during the pilot project, as we respond to feedback and work to improve the map.
Please Note:
Sections:
The Fire and Smoke Map shows fine particle pollution (PM2.5) from permanent AirNow monitors, temporary monitors deployed by agencies for smoke events, and low-cost sensors made by PurpleAir.
Users can click or tap on the layer icon (it looks like this
) on the upper right of the map to select/de-select map layers showing the different data sources.
To see other pollutants, visit the AirNow interactive map, which shows ozone, PM2.5, and PM10 data that official outdoor air quality air monitoring stations report to AirNow.
AirNow uses three shapes to show the type of air measurement device that is reporting data to the Fire and Smoke Map:
For each of the shapes, the map shows air quality in the color codes of the U.S. Air Quality Index. The color is determined using EPA’s NowCast.
The colors show the US. Air Quality Index (AQI) category, as calculated using EPA’s NowCast. The AQI is EPA’s color-coded tool for communicating air quality to the public. To see the AQI categories, click on the AQI Legend on the bottom left corner of the map. Note: If an icon is gray, that indicates that data is not available (this could occur for several reasons).
A quick glance at the Fire and Smoke Map will show you the latest NowCast Air Quality Index (AQI) category for monitor or sensor location. But there’s a lot more information available:
The AQI tab for each monitor or sensor displays the hourly Nowcast AQI value as well as the AQI color for the past 10 days. For low-cost sensors, the NowCast is applied after the sensor data are corrected.
The Concentration tab shows the PM2.5 concentration value for the current hour as well as the recent trend in concentrations over the past several days. For low-cost sensors, the concentrations shown have been corrected using the EPA correction equation.
Wildfire smoke can affect your health in many ways, but there are a number of different steps you can take to help protect yourself -- ranging from limiting outdoor activities to wearing masks to filtering indoor air via air conditioning or HEPA filters. Learn more about how wildfire smoke affects you and what you can do through at How Smoke from Fires Can Affect Your Health, or get more detailed information in the Wildfire Guide Factsheets.
To see the trend, click on the sensor or monitor you’re interested in. You’ll see a “dashboard” that shows a trend icon. Click on that icon for more detail.
We’ve added PM2.5 trend information to the dashboard in response to feedback we received during the 2020 sensor data pilot. Air quality can change rapidly during a fire and map users expressed interest in seeing more real-time air quality information to help them make decisions about their outdoor activities. The PM2.5 trend describes how conditions have changed recently – usually over the last 30 minutes.
The trend information you see when you click or tap on a monitor or sensor describes the most recent air quality information (usually gathered over the past 30 minutes) and can help give you an idea whether air quality near that location is stable, improving or getting worse.
The overall Fire and Smoke Map shows hourly particle pollution (PM2.5) levels in the color-coded categories of the Air Quality Index (AQI). The AQI for particle pollution is a 24-hour index that is tied to national standards for particle pollution (also called particulate matter) and the scientific studies behind them. To show the most recent hour of air quality as the AQI, AirNow uses a formula called a “NowCast” to estimate the AQI for the current hour.
While the trend information may more closely align with what you see outside your window than the NowCast, you should use them both to make decisions. When you click on a monitor or sensor on the map, you’ll see both current air quality, calculated using the NowCast, and the trend. The NowCast AQI category tells you who should take precautions to protect their health. The trend information shows you whether air quality for the past 30 minutes has been stable, improving or worsening at your location. You can use that to guide short-term activities, such as opening or closing windows, or going outside to walk the dog.
No. The PM2.5 short-term trend is not a forecast of NowCast categories. The trend shows what has recently been observed (usually in the past 30 minutes) at the location you have selected. The color code and category included in the trend show what the NowCast AQI category would be in the next few hours IF conditions continue to remain at these levels. If conditions change, the NowCast may not reach this category.
Sometimes observations in an area can show different PM2.5 trends. Sensors and monitors can reflect only the conditions at their specific location, but smoke can vary considerably -- even over small distances and times. This is particularly true as smoke plumes move in and out of an area. This can cause different trends at sensors or monitors in the same area – and can result in different NowCast AQI categories, too.
For a low-cost sensor, only data from that sensor is used to determine a trend. All 10-minute rolling averages received in the past 20 minutes from PurpleAir are recorded (note the 10- minute average from 20 minutes ago represents the time period from 30 to 20 minutes ago). Each 10-minute average is considered a separate data point and is converted into an AQI category based on its value. The range of these 10-min AQI categories is then used to evaluate the PM2.5 trend.
Calculation of PM2.5 trend for a permanent or temporary monitor is based on the recent data available from the nearest low-cost sensors, provided they are within 10 kilometers of the monitor. Up to three low-cost sensors are used. Where no low-cost sensor has been identified nearby, the last available hourly measurement from the monitor itself is used, provided it is no more than an hour old.
Calculating the PM2.5 trend requires having timely data. For instance, we need 10-minute data from the most recent 30 minutes (in real time) in the case of low-cost sensors and permanent/temporary monitors with sensors within 10 km. For permanent/temporary monitor with no nearby low-cost sensors, we need an hourly measurement within the last hour to report a trend. Sometimes due to data lags or other issues no such data is available; in this case the PM2.5 trend is listed as “not available.”
Depending on the situation, the PM2.5 trend label can be stable, increasing, decreasing, or variable. The trend graphic (see below) also shows the AQI category range for the data used to determine the trend.
Here are descriptions of the trend categories.
To minimize the possibility that small fluctuations in air quality are mis-interpreted as an increasing or decreasing trend, we use a 10 percent “buffer” around each NowCast AQI breakpoint. This means we do not label a trend as increasing or decreasing until data show PM2.5 concentrations are 10 percent higher than the concentration breakpoint between two NowCast AQI categories.
The written trend description states the full range of AQI categories observed in the past 30 minutes. It is possible that rapid changes in air quality may result in 30 minutes of data that span several AQI categories. If this happens, the PM2.5 trend description will list the full range of categories observed (e.g. GOOD-MODERATE). The PM2.5 trend icon circle color will always represent the category within this range that is the closest to the current NowCast AQI category at the sensor or monitor. This may be the same as the current NowCast AQI if that category was observed in the recent data.
The Fire and Smoke map brings you a host of fire-related information all in one place, including:
In 2021, EPA and the U.S. Forest Service have expanded the information available when you click or tap a monitor or sensor icon. We’ve added a dashboard” that gives you quick access to key information you can use to help plan your activities: the current AQI category at a monitor or sensor location; information about actions to consider taking; and information showing whether air quality is getting better or worse. You also can find a map showing the monitor or sensor location, and ID information about the particular monitor or sensor you have selected.
USFS and EPA are providing the sensor data on the Fire and Smoke Map to give the public additional information they can use to make individual decisions to protect their health during fires. Sensor data is not currently used on other maps on the AirNow website and is not used to generate the current NowCast Air Quality Index (AQI) or the forecast AQI shown on the “dial” on the AirNow home page or AirNow app. The data on the map is not used for regulatory purposes.
While you may use both websites to learn more about air quality in your area, the AirNow Fire and Smoke Map allows you to compare current air quality from low-cost sensors, permanent monitors that report to AirNow, and temporary monitors – and to see all of that information in one place. In addition, the Fire and Smoke Map features fire location, basic fire information (if available), and smoke plume information.
In addition, the maps may look different because of:
Differences in sensor data processing:
USFS and EPA take several steps before sensor data appear on the Fire and Smoke Map:
When clicking on individual sensors on the Fire and Smoke Map, you can view the hourly Nowcast for the past several days, along with 1-hour, and 10-minute averages in PM2.5 concentrations.
The PurpleAir map shows outdoor and indoor sensors. Users can also choose to view the data in different averaging times (down to 2-minute averages), to apply several corrections and conversions, or view additional data such as PM10, particle count, temperature, and relative humidity data. Viewing data at different averaging intervals and using different corrections can cause differences between the maps. In addition, PurpleAir uses a different color scale to display their data.
To learn more, watch our video at https://www.youtube.com/watch?v=5prwxe1U9GY&t=484s
Air sensors, also known as low-cost sensors, are a class of non-regulatory technology for measuring pollutants in the air. This term often describes an integrated set of hardware and software that uses one or more “sensing elements” (also sometimes called sensors) to detect or measure pollutant concentrations. Air sensors are lower in cost, portable, and generally easier to operate than the regulatory monitors widely used in the United States. Learn more about sensors at https://www.epa.gov/air-sensor-toolbox.
The NowCast Air Quality Index or PM2.5 concentration reported by a monitor or sensor represents the air quality at the monitor/sensor location for a given day and time. Whether air quality where you are is exactly the same depends on many factors including how far away you are from the monitor/sensor location, meteorological conditions like wind speed and wind direction, geographic features like terrain, the location of PM2.5 sources, and the size and amount of the particles emitted.
If PM2.5 concentrations are fairly stable, no significant winds are present, and no PM sources are near or between you and the monitor/sensor, you may expect that your air quality may be similar to the monitor/sensor several kilometers away. However, if PM2.5 concentrations are highly variable, if smoke plumes are in the area, or if PM sources are nearby, and/or if there is significant terrain like mountains/hills and valleys, there may be larger differences in air quality between your location and the nearest monitor or sensor. You may even see this type of difference when comparing two nearby sensors.
The sensor data comes from PurpleAir, which crowdsources data from that company’s particle pollution sensors and shows the data on a map. Only PurpleAir sensors that are registered as outdoor and display publicly will appear on the AirNow Fire and Smoke Map. EPA and USFS perform quality control screening and then apply some data processing steps, a scientific correction equation to reduce bias in the sensor data, and the NowCast, the calculation used show the data in the context of the Air Quality Index.
There are several possible reasons why no sensor appear on the map for your area. There may be no publicly available sensors in your area, the sensors in your area failed to meet the quality control screening criteria developed for the Fire and Smoke Map, or the sensor data is temporarily unavailable or offline. Newly registered sensors also may not appear on the map for up to 48 hours. Sensors identified by state, local, or tribal agencies as problematic (such as sensors that are strongly influenced by local pollution sources, sensors that have shown erroneous data for a long time compared to other nearby sensors, or sensors believed to be mis-labeled or mis-located) may be removed from the map. It also is possible that the state, local or tribal agency responsible for air quality in your area has chosen not to have sensor data shown on the Fire and Smoke Map for your area. To date, only one state has chosen not to show PurpleAir data on the map.
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.
Sensor data was added to the Fire and Smoke Map during a pilot phase in 2020 using the PurpleAir sensor as a test. At the time, EPA and more than 30 state, local, and tribal air agency partners were operating these sensors side-by-side with highly robust and accurate regulatory monitors in more than 70 locations throughout the U.S. to evaluate their performance. Additionally, EPA conducted similar comparisons during smoke events in several locations throughout the U.S. The PurpleAir sensors were assessed because their use was growing exponentially, resulting in an extensive network of publicly reporting sensors worldwide, and EPA and our air monitoring partners needed to better understand how to interpret the data produced.
Using all of the collocation data collected, from typical ambient conditions AND smoke impacted conditions, EPA researchers used a scientific approach to develop a correction equation for PM2.5 data from PurpleAir sensors to make the data more comparable to the permanent and temporary monitors. This work allowed for a consistent view of air quality across the various monitoring types shown on the map. Work is now underway to determine how additional sensor types can be added to the map in the future.
Note: Low-cost sensor data is being provided by PurpleAir and is subject to the capabilities and limitations of that system. Use of any data provider or system does not constitute endorsement or recommendation of that system. Mention of trade names or commercial products does not constitute EPA or USFS endorsement or recommendation for use.
Please visit Technical Approaches for the Sensor Data on the AirNow Fire and Smoke Map to view a series of video segments 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 equation, along with links to additional resources.
EPA is currently working to develop a process to allow other sensors to appear on the map. While that work is underway, it would be advantageous for manufacturers and others to continue collecting data side-by-side with highly robust and accurate regulatory monitors (known as collocated data), to demonstrate performance and comparability.
Because the Fire and Smoke Map is most widely used during wildfire and smoke events, it is imperative that collocation data be collected during smoke impacted times when concentrations may be very high. Because the map is always available, collocations capturing typical ambient conditions throughout the U.S. are also valuable. EPA’s Performance Testing Protocols, Metrics, and Target Values for Fine Particulate Matter Air Sensors Report provides guidance for setup and reporting of sensor performance by collocation.
Sensors are most valuable when they can fill in data gaps which could mean deployments in rural or remote locations and in locations without readily available or intermittent power or cellular connectivity. Sensor manufacturers may wish to consider these issues when designing sensor devices or data quality assurance or correction methodologies.
For additional information, visit Air Sensor Performance Targets and Testing Protocols.
State, local, and tribal air agencies are not responsible for the accuracy and performance of the sensor data. The Fire and Smoke Map shows publicly available PM2.5 (fine particle pollution) data provided by the PurpleAir data feed. Many PurpleAir sensors are run by community groups and individuals. Little is known about the sensors’ locations, including how accurate the user-reported GPS coordinates are or how close sensors are to any localized sources of pollution, or how the sensors are operated or maintained. That’s why you should use the sensor data on the map for informational purposes only.
While low-cost sensors are useful for providing general information about air quality, air sensors have a number of limitations that could include occasionally reporting questionable data points and a bias that may result in data that systematically over- or under-estimates the actual pollutant concentration. For the Fire and Smoke Map, we quality control sensor data to remove questionable data points and apply a correction equation to remove bias in the sensor data before showing sensor information on the map. These steps make the sensor data more comparable to data from permanent and temporary monitors. EPA does not use sensor data for regulatory purposes, and it should not be used for official daily AQI reporting.
You can learn more about key considerations about PurpleAir Sensors and Crowdsourced Data here: https://www.youtube.com/embed/5prwxe1U9GY?&start=1520&end=1906
No. For compliance with the National Ambient Air Quality Standards (NAAQS) compliance, methods must meet the applicable requirements in the Code of Federal Regulations (CFR) - Part(s) of Title 40, Protection of Environment (see, e.g. 40 CFR Parts 50, 53, and 58). Technical requirements include detailed sampling, siting, and quality assurance requirements. Only data from federal reference or equivalent method (FRM/FEM) monitors are used in a regulatory context.
Sensor data can have a number of limitations and uncertainties, including limitations in measurement technology, data bias and inaccuracy, sensor failure, and unknowns about siting and crowdsourcing.
Despite these limitations and uncertainties, EPA and USFS believe that sensor data is valuable during localized smoke episodes. Sensors report more frequently than regulatory-grade air quality monitors, and there are thousands of them, meaning they can provide air quality information in areas where there are no official monitoring stations. While a minor fraction of the sensors used in the Fire and Smoke Map may have issues, our experience indicates that data from most crowdsourced sensors will be of value for reporting air quality during wildfires.
More detail
Sensor data limitations include:
The extended U.S.-wide correction is a mathematical equation, developed by EPA scientists, that reduces the bias in the sensor data so that sensor data is more comparable with data from permanent and temporary monitors. This correction was built based from comparisons between sensors and permanent/temporary monitors across the U.S. during typical ambient time, smoke impacted times, and during extreme smoke episodes during the 2020 wildfire season. You can learn more about EPA’s work to update the U.S.-wide correction here: https://www.youtube.com/embed/G7CNziDkUok?&start=1641
More detail:
The extended correction is a piecewise regression that corrects for bias and relative humidity at low concentration and the nonlinearity of PurpleAir response at higher concentration. Although originally developed on the cf_1 data it is being implemented on the cf_atm data since 10-minute averages are not currently available for the cf_1 data. Additional details on the correction can be found on the air sensor toolbox (https://www.epa.gov/air-sensor-toolbox/technical-approaches-sensor-data-airnow-fire-and-smoke-map).
| Low Concentration PAcf_atm < 50 µg/m3 |
PM2.5 = 0.52 x (PAcf_atm) - 0.086 x RH + 5.75 |
| Mid Concentration 50 µg/m3 ? (PAcf_atm) <229 | PM2.5 = 0.786 x (PAcf_atm) - 0.086 x RH + 5.75 |
| High Concentration PAcf_atm ? 229 µg/m3 |
PM2.5 = 0.69 x (PAcf_atm) + 8.84 x 10-4 x PAcf_atm2 + 2.97 |
Active large fire incidents from the U.S. National Interagency Fire Center’s active incident feed are shown as fire icons (shown as 
for large incidents and
for satellite-detected fires). Clicking on a fire icon displays information about the fire. Note that these incidents may not have updated for several days due to the nature of the reporting systems used. Additional information on these incidents is available through the InciWeb system (https://inciweb.nwcg.gov). While the information presented by this feed can be several days old, it does provide important management information including the fire name, overall fire size, and containment.
Fire and smoke plume detections are from the NOAA’s Hazard Mapping System Fire and Smoke Products. Trained analysts manually integrate data from various automated fire detection algorithms with information from satellite instruments, including NASA’s Geostationary Operational Environmental Satellite (GOES) Imager, NOAA’s Advanced Very High Resolution Radiometer (AVHRR) and NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS). The analyst outlines smoke plumes that are detected by the satellites, resulting in a quality-controlled display of fire locations and smoke plumes. The smoke plumes are updated every few hours.
Both the fire detections and the smoke plume data are generated by the Hazard Mapping System. Note that the information on fire position should be used as general guidance and for strategic planning, not for tactical decisions, such as the activation of a response to fight these fires and evacuation efforts, without other information to corroborate the fire's existence and location.
The NowCast is the calculation that EPA uses to relate hourly readings from air quality monitors to the U.S. Air Quality Index (AQI). EPA uses the NowCast to show you current air quality using the AQI colors and scale (the AQI for particle pollution is a 24-hour index). The NowCast for particle pollution shows you air quality for the most current hour available by using a calculation that involves multiple hours of past data. It uses longer averages during periods of stable air quality and shorter averages when air quality is changing rapidly, such as during a wildfire. See the calculation.
The NowCast AQI shows air quality for the most current hour available by using a calculation that involves multiple hours of past data. The NowCast uses longer averages during periods of stable air quality and shorter averages when air quality is changing rapidly, such as during a wildfire. The PM2.5 value is a 1-hour average concentration measured by an air quality monitor.
The Interagency Wildland Fire Air Quality Response Program provides Air Resource Advisors (ARAs) that work with Incident Management Teams responding to large wildfires. Most large and persistent wildfires have ARAs assigned. ARAs analyze, summarize, and communicate smoke impacts to incident management teams, air quality regulators, public health agencies, and the public. ARAs issue these Special Smoke Statements (also known as Smoke Outlooks) for areas where smoke from wildfires may be of concern and they have been deployed. At this time, only Special Smoke Statements issued by ARAs are provided in the map. However, additional information on smoke impacts can be available at your state, tribal, or local air quality agency. Learn more about ARAs and what they do.
For additional information about wildfire smoke and air quality near you, please contact your state, tribal, or local air quality agency and/or local public health agencies for additional air quality information and air quality alerts.
Thank you for taking the time to provide feedback on the pilot effort by USFS and EPA to add a sensor data layer to the Fire and Smoke Map.
Please email feedback to: firesmokemap@epa.gov
