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Four Highest Eight-Hour Ozone Concentrations in 2021
as of October 18

Use this form to retrieve the four highest eight-hour ozone concentration averages from data collected at DAQ monitoring sites beginning January 1, 1999 through today. Although this is our most current data, it is not considered official until it has been certified by our technical staff. This information is updated hourly. All times shown are in Local Standard Time.

The table below lists the four highest daily maximum eight-hour ozone concentrations measured in 2021 in each community where the DAQ measures ozone. Concentrations that are rated Moderate or higher are color-highlighted based on the EPA-defined Air Quality Index colors. (See Interpreting the AQI.) The fourth-highest average is in bold black (unless it is highlighted). All ozone measurements are in parts per billion. Times are shown in 24-hour format and correspond to the beginning of the eight hour average.

Use the selection boxes below to customize this report. You may select a different year or a different report format. If you want to cut and paste data from this web page into another application, such as a spreadsheet, select the comma-delimited format. Click on the Generate Report button once you have made your selections.

YearReport Format
Highlight with AQI colors
Area Monitoring Site POC Highest Second Highest Third Highest Fourth Highest
Date Time Value Date Time Value Date Time Value Date Time Value
Clark County
Virgin Valley108/07/202110007308/03/202110006506/10/202111006505/01/2021110065
Paul Meyer108/07/202109008108/14/202110007808/03/202111007708/22/2021100074
Mountains Edge108/07/202109008008/03/202110008008/02/202110007506/17/2021100075
Walter Johnson108/07/202109008208/19/202110007808/02/202110007708/22/2021110075
Palo Verde108/07/202109008308/14/202110007808/02/202110007808/19/2021110076
Joe Neal108/07/202110008308/19/202110008208/22/202111007508/02/2021100075
Green Valley108/07/202110008408/22/202111007408/02/202111007408/03/2021100072
Liberty High School108/07/202110008208/02/202111007708/03/202111007608/22/2021110074
Jerome Mack108/07/202110007608/02/202111007208/22/202111007008/19/2021110070
Garrett Junior High106/10/202112007208/01/202112007006/18/202109006905/29/2021110069
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.