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Eight-Hour Ozone High Value Days for 2021
as of June 18

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 DAQ 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
2021 Sorted by Maximum Value
LocationRegionCAMSAQSDateTimeValuePOC
Mountains Edge 1 4432_003_0044June 17 202110:00751
Palo Verde 1 7332_003_0073June 3 202109:00741
Palo Verde 1 7332_003_0073June 16 202110:00741
Joe Neal 1 7532_003_0075June 11 202111:00731
Indian Springs 1 777232_003_7772May 14 202111:00731
Paul Meyer 1 4332_003_0043June 11 202111:00721
Paul Meyer 1 4332_003_0043June 17 202111:00721
Walter Johnson 1 7132_003_0071June 3 202109:00721
Walter Johnson 1 7132_003_0071June 11 202111:00721
Joe Neal 1 7532_003_0075June 16 202110:00721
Garrett Junior High 1 60232_003_0602June 10 202112:00721
Walnut 1 200332_003_2003June 2 202110:00721
Walnut 1 200332_003_2003June 11 202111:00721
Paul Meyer 1 4332_003_0043June 16 202110:00711
Walter Johnson 1 7132_003_0071May 29 202111:00711
Walter Johnson 1 7132_003_0071June 12 202109:00711
Walter Johnson 1 7132_003_0071June 16 202110:00711
Palo Verde 1 7332_003_0073June 12 202110:00711
Joe Neal 1 7532_003_0075May 29 202110:00711
Joe Neal 1 7532_003_0075June 3 202109:00711
Joe Neal 1 7532_003_0075June 4 202109:00711
Green Valley 1 29832_003_0298June 11 202111:00711
POC (Parameter Occurrence Code): a code used to correctly separate data from multiple instruments at one site.

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 0.201 - 0.2011
401 - 500 0.505 - 0.604 Not Defined
500+ Not Defined Not Defined

PLEASE NOTE: This data has not been verified by the Clark County Department of Air Quality 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 Clark County Department of Air Quality 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.