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The U. S. Environmental Protection Agency (EPA) has provided a scale called the Air Quality Index (AQI) for rating air quality. This scale is based on the National Ambient Air Quality Standards (NAAQS) and is described in the Code of Federal Regulations, Part 58, Appendix G. This report is based on the AQI standards. More information on the AQI can be found on the EPA's AirNow web site.
PLEASE NOTE: Data in this table are collected from air monitoring sites in Texas where data are reported to EPA. Site-specific information is available for each site by clicking on the site name. These data have not been verified by the TCEQ or the responsible entity and may change. While these are the most current data, they are not official until they have been certified by the appropriate technical staff. This table is updated hourly. Click here for information about all the monitoring sites.
The table above lists the current peak concentrations for each pollutant, the corresponding Air Quality Index (AQI) category, and the AQI ratings for each of the NAAQS pollutants that are measured real-time. The table is updated each hour and covers the period from midnight through the indicated ending time for today's data or from midnight to midnight on other days. Listings are provided for each monitoring site within the Austin-San Marcos metropolitan area where pollutant levels are monitored by the TCEQ.
Each NAAQS pollutant has a separate AQI scale, with an AQI rating of 100 corresponding to the concentration of the Federal Standard for that pollutant. Additional information about the AQI and how it can be used is available from the EPA's AirNow web site.
Place your mouse pointer over the scale displayed above to view information about the Air Quality Index, and each of the rating levels.
The actual index calculation is different for each parameter measured and is specified by the EPA. The following table shows the various breakpoints used in calculating the AQI.
|AQI Breakpoint Definitions|
|AQI Range||1hr Ozone
|8hr Carbon Monoxide
|1hr Sulfur Dioxide
|24hr Sulfur Dioxide
|1hr Nitrogen Dioxide
in µg/m³ (25° C)
in µg/m³ LC
|0 - 50||Not Defined||0 - 0.054||0 - 4.4||0 - 0.035||Not Defined||0 - 0.053||0 - 54||0 - 12.0|
|51 - 100||Not Defined||0.055 - 0.070||4.5 - 9.4||0.036 - 0.075||Not Defined||0.054 - 0.1||55 - 154||12.1 - 35.4|
|101 - 150||0.125 - 0.164||0.071 - 0.085||9.5 - 12.4||0.076 - 0.185||Not Defined||0.101 - 0.36||155 - 254||35.5 - 55.4|
|151 - 200||0.165 - 0.204||0.086 - 0.105||12.5 - 15.4||0.186 - 0.304||Not Defined||0.361 - 0.64||255 - 354||55.5 - 150.4|
|201 - 300||0.205 - 0.404||0.106 - 0.200||15.5 - 30.4||Not Defined||0.305 - 0.604||0.65 - 1.24||355 - 424||150.5 - 250.4|
|301 - 400||0.405 - 0.504||Not Defined||30.5 - 40.4||Not Defined||0.605 - 0.804||1.25 - 1.64||425 - 504||250.5 - 350.4|
|401 - 500||Not Defined||Not Defined||40.5 - 50.4||Not Defined||0.805 - 1.004||1.65 - 2.04||505 - 604||350.5 - 500.4|
|500+||Not Defined||Not Defined||Not Defined||Not Defined||Not Defined||Not Defined||605 - 4999||500.5 - 999.9|
PLEASE NOTE: This data has not been verified by the TCEQ and may change. This is the most current data, but it is not official until it has been certified by our technical staff. Data is collected from TCEQ ambient monitoring sites and may include data collected by other outside agencies. This data is updated hourly. All times shown are in local standard time unless otherwise indicated.
Following EPA reporting guidelines, negative values may be displayed in our hourly criteria air quality data beginning 1/1/2013, down to the negative of the EPA listed Method Detection Limit (MDL) for the particular instrument that made the measurements. The reported concentrations can be negative due to zero drift in the electronic instrument output, data logger channel, or calibration adjustments to the data. Prior to 1/1/2013, slightly negative values were automatically set to zero.