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Eight-Hour Ozone High Value Days for 2025
as of July 1

The table below lists the daily maximum eight-hour ozone concentrations measured which meet or exceed 71 parts per billion in 2025 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.

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YearSort ByReport Format
Highlight with AQI colors
2025 Sorted by Maximum Value
LocationRegionCAMSAQSDateTimeValuePOC
Elm Creek Elementary C501 13 50148_029_0501June 24 202508:00991 N
Galveston 99th St. C1034/A320/X183 12 103448_167_1034March 1 202516:00971
HRM-3 Haden Road C603/A114 12 60348_201_0803June 20 202516:00961 N
West Houston C554 12 55448_201_0554May 29 202510:00881 N
Mercer Arboretum C557 12 55748_201_0557May 27 202510:00881 N
AACOG City of Garden Ridge C505 13 50548_091_0505May 12 202512:00861 N
Mercer Arboretum C557 12 55748_201_0557March 25 202510:00861 N
Frisco C31/C680 4 3148_085_0005June 16 202513:00851
Meyer Park C561 12 56148_201_0561March 25 202510:00851 N
Heritage Middle School C622 13 62248_029_0622May 12 202511:00831 N
Galveston 99th St. C1034/A320/X183 12 103448_167_1034May 12 202514:00831
Killeen Skylark Field C1047 9 104748_027_1047May 13 202512:00821
Galveston 99th St. C1034/A320/X183 12 103448_167_1034February 1 202512:00821
West Houston C554 12 55448_201_0554May 7 202509:00821 N
Bulverde Elementary C503 13 50348_091_0503May 15 202511:00811 N
Pilot Point C1032 4 103248_121_1032May 23 202510:00811
Houston Aldine C8/AF108/X150 12 848_201_0024March 25 202510:00812
West Houston C554 12 55448_201_0554May 21 202509:00801 N
Huffman Wolf Road C563 12 56348_201_0563March 25 202510:00801 N
Conroe Relocated C78/A321 12 7848_339_0078April 10 202511:00801
Conroe Relocated C78/A321 12 7848_339_0078April 12 202511:00801
Frisco C31/C680 4 3148_085_0005May 23 202510:00791
Ascarate Park SE C37/A332/A172/X159 6 3748_141_0055May 11 202511:00791
Mercer Arboretum C557 12 55748_201_0557April 10 202509:00791 N
Lang C408 12 40848_201_0047May 29 202511:00782
Mercer Arboretum C557 12 55748_201_0557April 9 202510:00781 N
Mercer Arboretum C557 12 55748_201_0557June 2 202509:00781 N
Huffman Wolf Road C563 12 56348_201_0563May 27 202509:00781 N
Dripping Springs School C614 11 61448_209_0614May 21 202511:00781 N
Conroe Relocated C78/A321 12 7848_339_0078April 9 202510:00781
Conroe Relocated C78/A321 12 7848_339_0078June 2 202510:00781
Northwest Harris Co. C26/A110/X154 12 2648_201_0029March 25 202512:00772
Mercer Arboretum C557 12 55748_201_0557April 12 202509:00771 N
Tom Bass C558 12 55848_201_0558March 1 202512:00771 N
Katy Park C559 12 55948_201_0559May 21 202509:00771 N
Dripping Springs School C614 11 61448_209_0614April 9 202511:00771 N
Dripping Springs School C614 11 61448_209_0614April 11 202511:00771 N
Bulverde Elementary C503 13 50348_091_0503May 13 202511:00761 N
Bulverde Elementary C503 13 50348_091_0503May 14 202511:00761 N
AACOG City of Garden Ridge C505 13 50548_091_0505May 13 202511:00761 N
Skyline Park C72 6 7248_141_0058May 11 202511:00761
Northwest Harris Co. C26/A110/X154 12 2648_201_0029April 9 202510:00762
Houston East C1/G316 12 148_201_1034March 25 202510:00762
Dripping Springs School C614 11 61448_209_0614April 8 202512:00761 N
Dripping Springs School C614 11 61448_209_0614May 13 202511:00761 N
Granbury C73/C681 4 7348_221_0001April 10 202512:00761
Conroe Relocated C78/A321 12 7848_339_0078March 25 202511:00761
Camp Bullis C58 13 5848_029_0052April 11 202511:00751
Frisco C31/C680 4 3148_085_0005May 13 202512:00751
Dallas North No.2 C63/C679 4 6348_113_0075June 16 202510:00751
Texas City 34th St. C620 12 62048_167_0056March 1 202512:00751 N
Texas City 34th St. C620 12 62048_167_0056May 12 202513:00751 N
Longview C19/A127/C644 5 1948_183_0001April 9 202513:00752
Lang C408 12 40848_201_0047March 25 202511:00752
Meyer Park C561 12 56148_201_0561April 10 202510:00751 N
Dripping Springs School C614 11 61448_209_0614April 21 202511:00751 N
Laredo College C44 16 4448_479_0016May 15 202511:00751 N
Killeen Skylark Field C1047 9 104748_027_1047April 12 202511:00741
Government Canyon C1610 13 161048_029_1610April 11 202511:00741 N
Government Canyon C1610 13 161048_029_1610April 21 202511:00741 N
Government Canyon C1610 13 161048_029_1610May 21 202510:00741 N
Lockhart C1604 11 160448_055_1604April 9 202511:00741 N
Pilot Point C1032 4 103248_121_1032May 13 202512:00741
Northwest Harris Co. C26/A110/X154 12 2648_201_0029April 12 202511:00742
West Houston C554 12 55448_201_0554March 25 202510:00741 N
Meyer Park C561 12 56148_201_0561April 12 202509:00741 N
Huffman Wolf Road C563 12 56348_201_0563April 10 202509:00741 N
Eagle Mountain Lake C75 4 7548_439_0075May 23 202511:00741
Ft. Worth Northwest C13/AH302 4 1348_439_1002May 23 202510:00742
Laredo College C44 16 4448_479_0016May 12 202510:00741 N
Calaveras Lake C59 13 5948_029_0059May 12 202511:00731
Heritage Middle School C622 13 62248_029_0622April 21 202511:00731 N
Heritage Middle School C622 13 62248_029_0622May 20 202513:00731 N
Seguin Outdoor Learning Center C506 13 50648_187_0506May 12 202512:00731 N
Meyer Park C561 12 56148_201_0561April 9 202509:00731 N
Bunker Hill Village C562 12 56248_201_0562May 21 202509:00731 N
Rockwall Heath C69 4 6948_397_0001June 16 202511:00731
Grapevine Fairway C70/A301/X182 4 7048_439_3009May 23 202510:00731
Fair Oaks Ranch C502 13 50248_029_0502April 11 202512:00721 N
Heritage Middle School C622 13 62248_029_0622April 11 202511:00721 N
Government Canyon C1610 13 161048_029_1610May 12 202510:00721 N
Frisco C31/C680 4 3148_085_0005May 14 202510:00721
Lang C408 12 40848_201_0047May 7 202509:00722
Houston Harvard Street C417 12 41748_201_0417March 25 202511:00721
West Houston C554 12 55448_201_0554April 9 202509:00721 N
HRM-3 Haden Road C603/A114 12 60348_201_0803March 25 202510:00721 N
Dripping Springs School C614 11 61448_209_0614April 12 202511:00721 N
Dripping Springs School C614 11 61448_209_0614May 20 202511:00721 N
Waco Mazanec C1037 9 103748_309_1037April 9 202511:00721
Conroe Relocated C78/A321 12 7848_339_0078April 16 202510:00721
Conroe Relocated C78/A321 12 7848_339_0078June 9 202511:00721
Ft. Worth Northwest C13/AH302 4 1348_439_1002April 10 202511:00722
Keller C17 4 1748_439_2003March 1 202511:00722
Killeen Skylark Field C1047 9 104748_027_1047April 9 202511:00711
Killeen Skylark Field C1047 9 104748_027_1047May 14 202511:00711
Camp Bullis C58 13 5848_029_0052May 15 202511:00711
Camp Bullis C58 13 5848_029_0052May 21 202510:00711
Elm Creek Elementary C501 13 50148_029_0501April 21 202511:00711 N
Fair Oaks Ranch C502 13 50248_029_0502April 10 202511:00711 N
Government Canyon C1610 13 161048_029_1610May 13 202511:00711 N
Lockhart C1604 11 160448_055_1604April 8 202510:00711 N
Lockhart C1604 11 160448_055_1604May 20 202512:00711 N
AACOG City of Garden Ridge C505 13 50548_091_0505April 11 202511:00711 N
AACOG City of Garden Ridge C505 13 50548_091_0505May 15 202511:00711 N
Dallas Executive Airport C402 4 40248_113_0087May 7 202511:00711
Ascarate Park SE C37/A332/A172/X159 6 3748_141_0055June 16 202511:00711
Houston Aldine C8/AF108/X150 12 848_201_0024April 12 202510:00712
Northwest Harris Co. C26/A110/X154 12 2648_201_0029April 10 202510:00712
Houston Harvard Street C417 12 41748_201_0417May 29 202511:00711
Crosby Library C553 12 55348_201_0553April 10 202508:00711 N
La Porte Sylvan Beach C556 12 55648_201_0556May 12 202512:00711 N
Atascocita C560 12 56048_201_0560March 25 202509:00711 N
Meyer Park C561 12 56148_201_0561May 27 202510:00711 N
Bunker Hill Village C562 12 56248_201_0562May 29 202510:00711 N
Baytown Garth C1017 12 101748_201_1017March 25 202510:00711
Dripping Springs School C614 11 61448_209_0614April 10 202511:00711 N
Mission C43/AP143 15 4348_215_0043April 8 202510:00711
Mission C43/AP143 15 4348_215_0043May 12 202510:00711
Cleburne Airport C77/C682 4 7748_251_0003April 10 202512:00711
Waco Mazanec C1037 9 103748_309_1037May 13 202511:00711
St. Edwards University C1605 11 160548_453_1605April 8 202511:00711 N
St. Edwards University C1605 11 160548_453_1605April 11 202511:00711 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.