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Outdoor Air Quality Data

Air Data Basic Information

On this page:

What is AirData?

The AirData website gives you access to air quality data collected at outdoor monitors across the United States, Puerto Rico, and the U. S. Virgin Islands. The data comes primarily from the AQS (Air Quality System) database. You can choose from several ways of looking at the data:

  • download data into a file (or view it on the screen)
  • output the data into one of AirData’s standard reports
  • create graphical displays using one of the visualization tools
  • investigate monitor locations using an interactive map

AirData assists a wide range of people, from the concerned citizen who wants to know how many unhealthy air quality days there were in his county last year to air quality analysts in the regulatory, academic, and health research communities who need raw data.

AirData lets you display and download monitored hourly, daily, and annual concentration data, AQI data, and speciated particle pollution data. For more detailed information on the AQS and the AirData source information, you can refer to the About AQS Data page.  If you need data that AirData does not have (such as emissions data) please see Other Sources of Data.

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Keeping Up with AirData News

We invite you to subscribe to the AirData RSS Feed so you’ll be notified when we make enhancements to AirData, when we’re going to be down for scheduled maintenance, etc. 

Subscribe to the AirData RSS feed

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What Can I do with AirData?

There are four main parts of the AirData website: Download Data, Reports (Summary and Technical), Visualize Data, and the Interactive Map. 

Download Data

This part of the website has two query tools (one for raw data and one for daily data) and a page of pre-pulled data files.

Reports - Summary

This part of the website provides a way to generate customized reports based on parameters you select. The About Air Data Reports page explains exactly what is in each report, including individual column descriptions.

  • Air Quality Index Report – This report displays a yearly summary of AQI values in a county or city (specifically a CBSA - Core Based Statistical Area) . The summary values include maximum, 90th percentile and median AQI, the count of days in each AQI category, and the count of days when the AQI could be attributed to each criteria pollutant.
  • Air Quality Statistics Report – This report shows yearly summaries of air pollution values for a city or county. The report shows the highest values reported during the year by all monitors in the CBSA or county. The report uses highlighted text to show values that exceed the level of an air quality standard.
  • Monitor Values Report – This report shows a yearly summary (first through fourth maximum values, number of samples, etc.) of the measurements at individual monitors and provides descriptive information about the sites.
  • Monitor Values Report - Hazardous Air Pollutants – This report displays hazardous air pollutant summary data for individual monitoring sites.
  • Air Quality Index Daily Values Report – This report provides daily Air Quality Index values for the specified year and location.

Reports - Technical

This part of the website provides a way to generate customized reports based on parameters you select.  These reports are technical in nature and are intended to assist monitoring agencies.

Visualize Data

Sometimes “seeing” the data is the best way to understand it. AirData’s visualization tools display data in unique and helpful ways.

  • AQI Plot - Compare AQI values for multiple pollutants for a specific location and time period. This tool displays an entire year of AQI values – two pollutants at a time - and is useful for seeing how the number of unhealthy days can vary throughout the year for each pollutant.
  • Tile Plot - Plot daily AQI values for a specific location and time period. Each square or “tile” represents one day of the year and is color-coded based on the AQI level for that day.  The legend tallies the number of days in each AQI category.
  • Concentration Plot - Generate a time series plot for a specific location and time period. This tool displays daily air quality summary statistics for the criteria pollutants by monitor. You can choose to plot all monitors in a county or CBSA, or you can select specific monitors.
  • Concentration Map - Generate an animated series of daily concentration maps for a specific time period. Daily air quality is displayed in terms of the Air Quality Index (AQI) for the criteria pollutants, or in concentration ranges for certain PM species like organic carbon, nitrates, and sulfates.  This tool may be useful for tracking an air pollution episode like a wildfire event.
  • Ozone Exceedances - Compare 8-hour ozone "exceedances" from this year with previous years. Comparisons are presented in three ways. The first plot shows the comparisons by MONTH. The second plot shows the comparisons by DAY (for cumulative counts). The third plot shows the comparisons by YEAR.

The Interactive Map

Use the Interactive Map of Air Quality Monitors  to see where air quality monitors are located, get information about the monitor, and download data from the monitor.  You can select which monitoring networks to display on the map. There are also layers for nonattainment areas, Tribal areas, and Federal Class 1 areas (national parks and wilderness areas).

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Other Sources of Air Data

Name Type of Data
AirNow Exit Air quality forecasts and real-time data in a visual format for public health protection
AirCompare Exit AQI summaries for comparison of counties
AirTrends Trends of air quality and emissions
The National Emissions Inventory Emissions - a comprehensive and detailed estimate of air emissions of both Criteria and Hazardous air pollutants from all air emissions sources
Air Quality System (AQS) Monitored ambient air quality data from AQS; for those who need large volumes of data
Power Sector Emissions, Operations, and Environmental Data Emissions and operating data from power plants since 1990, plus ambient data to track changes in the environment since the mid-1980s. 
CASTNET The Clean Air Status and Trends Network (CASTNET) is the nation's primary source for data on dry acidic deposition and rural, ground-level ozone
Remote Sensing Information Gateway (RSIG) Air quality monitoring, modeling, and satellite data
Radiation Monitoring Data Air quality and emissions; Links to databases and maps
EPA Data Finder Air, Water, other EPA data
Visibility Information Exchange Web System (VIEWS) Exit Air quality monitoring, modeling, emissions, and satellite data
Data.Gov Exit Air, Water, other U.S. Federal Executive Branch datasets

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Some Basic Air Quality Concepts

Here are a few basic air quality concepts that could help you when using AirData. 

Types of Data

Monitoring Data - Ambient (outdoor) concentrations of pollutants are measured at more than 4000 monitoring stations owned and operated mainly by state environmental agencies. The agencies send hourly or daily measurements of pollutant concentrations to EPA's database called AQS (Air Quality System). AirData retrieves data from AQS.

Emissions Data - EPA keeps track of the amount of pollution that comes from a variety of sources such as vehicles, power plants, and industries. The emissions data reported to EPA by state environmental agencies can be an actual reading taken at a source or an estimate made using a mathematical calculation. AirData does not contain emissions data at this time. Emissions data can be obtained from the Air Emissions Inventories website.

Types of Air Pollutants

Criteria Air Pollutants
EPA sets national air quality standards for six common pollutants, also called criteria pollutants, to protect public health. Monitoring sites report data to EPA for these six criteria air pollutants:

  • Ozone (O3)
  • Particulate matter (PM10 and PM2.5)
  • Carbon monoxide (CO)
  • Nitrogen dioxide (NO2)
  • Sulfur dioxide (SO2)
  • Lead (Pb)

(PM10 includes particles less than or equal to 10 micrometers in diameter.  PM2.5 includes particles less than or equal to 2.5 micrometers and is also called fine particle pollution.)

Hazardous Air Pollutants (HAPs) / Toxic Air Pollutants
Hazardous air pollutants (HAPs) (also called toxic air pollutants or air toxics) are pollutants that are known or suspected to cause serious health problems such as cancer.  There are 188 hazardous air pollutants.  Examples of toxic air pollutants include benzene, which is found in gasoline; perchlorethlyene, which is emitted from some dry cleaning facilities; and methylene chloride, which is used as a solvent and paint stripper. Examples of other listed air toxics include dioxin, asbestos, toluene, and metals such as cadmium, mercury, chromium, and lead compounds. The National Air Toxics Assessment (NATA) is EPA's ongoing comprehensive evaluation of air toxics in the U.S.

The AQI (Air Quality Index)
AirData uses the Air Quality Index (AQI) in some of its reports and tables and to display data using the visualization tools. The AQI is an index for reporting daily air quality. It tells how clean or polluted the air is, and what associated health effects might be a concern, especially for ground-level ozone and particle pollution.

Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air quality with little potential to affect public health, while an AQI value over 300 represents hazardous air quality.

An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy-at first for certain sensitive groups of people, then for everyone as AQI values get higher.

The AQI is divided into six categories:

Air Quality Index
(AQI) Values
Levels of Health Concern Colors
When the AQI is in this range: ..air quality conditions are: symbolized by this color:
0-50 Good Green
51-100 Moderate Yellow
101-150 Unhealthy for Sensitive Groups Orange
151 to 200 Unhealthy Red
201 to 300 Very Unhealthy Purple
301 to 500 Hazardous Maroon

Each category corresponds to a different level of health concern. The six levels of health concern and what they mean are:

  • "Good" AQI is 0 - 50. Air quality is considered satisfactory, and air pollution poses little or no risk.
  • "Moderate" AQI is 51 - 100. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people. For example, people who are unusually sensitive to ozone may experience respiratory symptoms.
  • "Unhealthy for Sensitive Groups" AQI is 101 - 150. Although general public is not likely to be affected at this AQI range, people with lung disease, older adults and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults and children are at greater risk from the presence of particles in the air.
  • "Unhealthy" AQI is 151 - 200. Everyone may begin to experience some adverse health effects, and members of the sensitive groups may experience more serious effects.
  • "Very Unhealthy" AQI is 201 - 300. This would trigger a health alert signifying that everyone may experience more serious health effects.
  • "Hazardous" AQI greater than 300. This would trigger health warnings of emergency conditions. The entire population is more likely to be affected.

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