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High Ozone in Your Metro Area

This table summarizes high one-hour and eight-hour ozone averages in the metropolitan areas where the TCEQ monitors ozone.

Please Note: Data in this table is based on the number of monitors operating in an area, as well as on the severity of ozone.
This data should not be used to perform comparisons between cities or across years without factoring in the number of monitors.

The peak one-hour and eight-hour averages are color-highlighted based on the EPA-defined Air Quality Index colors. (See Interpreting the AQI.)

High Ozone Averages for 2014

   
Highlight with AQI colors
Metropolitan AreaOne-Hour Averages
>= 125 ppb
Eight-Hour Averages
>= 76 ppb
Peak ValueHigh DaysPeak ValueHigh Days
DateppbDateppb
Houston
Includes:
     Fort Bend County, TX
     Harris County, TX
     Liberty County, TX
     Montgomery County, TX
No averages at or above 125 05/03/2014806
Dallas
Includes:
     Collin County, TX
     Dallas County, TX
     Denton County, TX
     Ellis County, TX
     Hunt County, TX
     Kaufman County, TX
     Rockwall County, TX
No averages at or above 125 07/16/2014782
Fort Worth-Arlington
Includes:
     Hood County, TX
     Johnson County, TX
     Parker County, TX
     Tarrant County, TX
No averages at or above 125 07/23/2014913
San Antonio
Includes:
     Bexar County, TX
     Comal County, TX
     Guadalupe County, TX
No averages at or above 125 05/30/2014911
Austin-San Marcos
Includes:
     Bastrop County, TX
     Caldwell County, TX
     Hays County, TX
     Travis County, TX
     Williamson County, TX
No averages at or above 125 No averages at or above 76
El PasoNo averages at or above 125 No averages at or above 76
McAllen-Edinburg-MissionNo averages at or above 125 No averages at or above 76
Corpus Christi
Includes:
     Nueces County, TX
     San Patricio County, TX
No averages at or above 125 05/29/2014761
Beaumont-Port Arthur
Includes:
     Jefferson County, TX
     Orange County, TX
No averages at or above 125 05/02/2014802
Brownsville-Harlingen-San BenitoNo averages at or above 125 No averages at or above 76
Killeen-TempleNo averages at or above 125 No averages at or above 76
Galveston-Texas CityNo averages at or above 125 No averages at or above 76
BrazoriaNo averages at or above 125 05/29/2014821
Longview-Marshall
Includes:
     Gregg County, TX
     Harrison County, TX
No averages at or above 125 No averages at or above 76
WacoNo averages at or above 125 No averages at or above 76
LaredoNo averages at or above 125 No averages at or above 76
TylerNo averages at or above 125 No averages at or above 76
Victoria
Includes:
     Dewitt County, TX
     Goliad County, TX
     Victoria County, TX
No averages at or above 125 No averages at or above 76
Fayette County, TexasNo averages at or above 125 No averages at or above 76
Brewster County, TexasNo averages at or above 125 No averages at or above 76
Navarro County, TexasNo averages at or above 125 No averages at or above 76
JuarezNo averages at or above 125 No averages at or above 76
Ozone averages are reported in parts per billion (ppb).
The High Days columns represent the number of days where one-hour or eight-hour ozone averages were at or above the thresholds of 125 ppb and 76 ppb respectively.

What do the Numbers Mean?

The information in the table is composed of ozone measurements from monitoring sites across Texas. There are two averaging periods that are of interest for ozone: a one-hour average and an eight-hour average. There are national air quality standards that have been established by the EPA for both of these averaging periods.

For the one-hour ozone average, a threshold of 125 ppb has been used to determine high value days. For the eight-hour ozone average, a threshold of 76 ppb has been used. Only averages that are equal to or higher than one of these thresholds appear in this table. The High Days column is a count of the number of days each metropolitan area experienced high ozone measurements (either one-hour or eight-hour) for the selected year. Out of all the averages at or above the thresholds, the peak or highest one-hour and eight-hour averages and the date they occurred are shown.

Ozone formation tends to be highest from March through October. Before May, there will be few if any metropolitan areas with high ozone readings. Some metropolitan areas never experience high ozone. In either of these cases, the table will show "No averages at or above 125", or "No averages at or above 76".

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 - 0.059
51 - 100 Not Defined 0.06 - 0.075
101 - 150 0.125 - 0.164 0.076 - 0.095
151 - 200 0.165 - 0.204 0.096 - 0.115
201 - 300 0.205 - 0.404 0.116 - 0.374
301 - 400 0.405 - 0.504 Not Defined
401 - 500 0.505 - 0.604 Not Defined
500+ Not Defined Not Defined

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.