![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
About the PSI Chart
What does the chart tell me?
A Pollutant Standards Index chart shows daily maximum air pollution values for a county or metropolitan area, for a time period of one to twelve months.
Please note that EPA has replaced the Pollutant Standards Index. See Air Quality Index below for further information.
The Pollutant Standards Index (PSI) was a uniform way of reporting ambient concentrations of five major air pollutants (criteria pollutants) regulated by the Clean Air Act. Daily index values were calculated for each of the five pollutants, using ambient concentrations measured at air monitoring sites in each county. The highest of those index values was a county's PSI value, and the pollutant responsible for the highest index value was the "main pollutant." The PSI value for a metropolitan statistical area was determined by selecting the highest daily index value in all counties that comprise the MSA. Broad categories of potential health effects, due to the major air pollutants, were associated with ranges of PSI values. A Pollutant Standards Index chart shows all three types of information: daily PSI values and main pollutants, and health effects categories.
How can I customize the chart?
- Geographic Area
- The name of the geographic area previously selected is displayed
here. You can click on "change" to choose a different area.
- Date Range (required)
- Determines the dates included in a PSI chart. Select all of the
following:
- Starting Month, Year - Beginning date of the chart. Select a month and year from the lists provided.
- Number of Months - The length of time displayed in the chart. Select a number of months (1-12) from the list provided.
Air Quality Index
In July 1999, EPA replaced the PSI with the Air Quality Index (AQI). Be aware that the data displayed in an AirData PSI chart do not conform with the current EPA definition of AQI. The PSI data are presented only as a qualitative indicator of historical air quality.
For a comparison of the obsolete PSI with AQI, refer to the tables below. They list the index values and pollutant concentrations for each health category of PSI and AQI. A third table lists pollutant names and units of measure.
| Pollutant Standards Index (PSI) | ||||||
|---|---|---|---|---|---|---|
| Category | Good | Moderate | Unhealthful | Very Unhealthful | Hazardous | |
| Index Value | 0 - 50 | 51 - 100 | 101 - 200 | 201 - 300 | 301 - 400 | 401 - 500 |
| Pollutant | Concentration Ranges | |||||
| CO | 0 - 4.5 | 4.5 - 9 | 9 - 15 | 15 - 30 | 30 - 40 | 40 - 50 |
| NO2 | -- | -- | -- | .6 - 1.2 | 1.2 - 1.6 | 1.6 - 2.0 |
| O3 1-hour | 0 - .06 | .06 - .12 | .12 - .20 | .20 - .40 | .40 - .50 | .50 - .60 |
| PM 10 | 0 - 50 | 50 - 150 | 150 - 350 | 350 - 420 | 420 - 500 | 500 - 600 |
| SO2 | 0 - .03 | .03 - .14 | .14 - .30 | .30 - .60 | .60 - .80 | .80 - 1.0 |
| Air Quality Index (AQI) | |||||||
|---|---|---|---|---|---|---|---|
| Category | Good | Moderate | Unhealthy for Sensitive Groups | Unhealthy | Very Unhealthy | Hazardous | |
| Index Value | 0 - 50 | 51 - 100 | 101 - 150 | 151 - 200 | 201 - 300 | 301 - 400 | 401 - 500 |
| Pollutant | Concentration Ranges | ||||||
| CO | 0 - 4.4 | 4.5 - 9.4 | 9.5 - 12.4 | 12.5 - 15.4 | 15.5 - 30.4 | 30.5 - 40.4 | 40.5 - 50.4 |
| NO2 | -- | -- | -- | -- | 0.65 - 1.24 | 1.25 - 1.64 | 1.65 - 2.04 |
| O3 1-hour | -- | -- | .125 - .164 | .165 - .204 | .205 - .404 | .405 - .504 | .505 - .604 |
| O3 8-hour | 0 - .059 | .060 - .075 | .076 - .095 | .096 - .115 | .116 - .374 | -- | -- |
| PM 2.5 | 0 - 15.4 | 15.5 - 40.4 | 40.5 - 65.4 | 65.5 - 150.4 | 150.5 - 250.4 | 250.5 - 350.4 | 350.5 - 500.4 |
| PM 10 | 0 - 54 | 55 - 154 | 155 - 254 | 255 - 354 | 355 - 424 | 425 - 504 | 505 - 604 |
| SO2 | 0 - .034 | .035 - .144 | .145 - .224 | .225 - .304 | .305 - .604 | .605 - .804 | .805 - 1.004 |
| Pollutants | ||
|---|---|---|
| CO | Carbon Monoxide | parts per million |
| NO2 | Nitrogen Dioxide | parts per million |
| O3 1-hour | Ozone (average concentration for 1 hour) | parts per million |
| O3 8-hour | Ozone (average concentration for 8 hours) | parts per million |
| PM 2.5 | Particulate Matter (particle sizes 2.5 micrometers or less) | micrograms per cubic meter |
| PM 10 | Particulate Matter (particle sizes 10 micrometers or less) | micrograms per cubic meter |
| SO2 | Sulfur Dioxide | parts per million |