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Eight-Hour Ozone High Value Days for 2021
as of April 13

The table below lists the daily maximum eight-hour ozone concentrations measured which meet or exceed 71 parts per billion in 2021 in each community where the TCEQ measures ozone. This information is updated hourly. Concentrations are color-highlighted based on the EPA-defined Air Quality Index colors. (See Interpreting the AQI.) Times shown are in 24-hour format and are Local Standard Time. Our convention is that the time reflects the beginning of the eight-hour average. All ozone measurements are in parts per billion.

Use the selection boxes below to customize this report. You may select a different year, a different sorting order, or a different report format. Click on the Generate Report button once you have made your selections.

YearSort ByReport Format
Highlight with AQI colors
2021 Sorted by Maximum Value
Lang C408 12 40848_201_0047April 11 202111:00892
Houston Aldine C8/AF108/X150 12 848_201_0024April 11 202111:00862
Houston Harvard Street C417 12 41748_201_0417April 11 202111:00781
Camp Bullis C58 13 5848_029_0052April 11 202111:00761
Houston East C1/G316 12 148_201_1034April 11 202110:00762
UH Launch Trailer C1611 12 161148_201_1611April 11 202111:00761 N
Houston North Wayside C405 12 40548_201_0046April 11 202111:00751
Texas City 34th St. C620 12 62048_167_0056March 23 202111:00741 N
UH Moody Tower C695 12 69548_201_0695April 11 202110:00741 N
Conroe Relocated C78/A321 12 7848_339_0078April 12 202110:00731
San Antonio Northwest C23 13 2348_029_0032April 11 202111:00722
Bulverde Elementary C503 13 50348_091_0503April 11 202111:00721 N
Park Place C416 12 41648_201_0416April 11 202111:00721
Meyer Park C561 12 56148_201_0561April 11 202112:00711 N
Dripping Springs School C614 11 61448_209_0614April 11 202112:00711 N
UH WG Jones Forest C698 12 69848_339_0698April 12 202110:00711 N
POC (Parameter Occurrence Code): a code used to correctly separate data from multiple instruments at one site.
 N - Data from this instrument does not meet EPA quality assurance criteria and cannot be used for regulatory purposes.

Interpreting the AQI

Air Quality Index

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
in ppm
8hr Ozone
in ppm
0 - 50 Not Defined 0 - 0.054
51 - 100 Not Defined 0.055 - 0.070
101 - 150 0.125 - 0.164 0.071 - 0.085
151 - 200 0.165 - 0.204 0.086 - 0.105
201 - 300 0.205 - 0.404 0.106 - 0.200
301 - 400 0.405 - 0.504 Not Defined
401 - 500 Not Defined Not Defined
500+ Not Defined Not Defined
  • The AQI for ozone is based on either the peak eight-hour running average since midnight OR the peak one-hour measurement since midnight.

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, 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.