About These Data
Date/Time of Measurements
Individual Live Sites Web pages display near real-time meteorology and pollutant
measurements. The date and time stamp posted under the image denotes
the last time an instrument was polled. Each monitoring station is accessed hourly to poll standard-time ozone
(O3), nitrogen dioxide (NO2), and meteorological 1-hour
averages (labeled for the "hour-beginning"). Those stations with particulate monitors are
accessed daily to poll the previous day’s 24-hour PM10 average. All monitoring station air quality data
depicts raw hourly, 8-hour, and 24-hour averages that have not been
validated. Whenever instrument data is designated invalid an “N/A” will appear on the page for that hour's reading.
These invalid readings are not considered in the rolling 8-hour or 24-hour average measurements.
Ongoing 8-hour and 24-hour rolling averages are based on the criteria that a minimum of
75% of the hourly data points have been collected to represent the rolling period. A minimum of 6 hourly data
points must have been collected to represent any rolling 8-hour period. A minimum of 18 hourly averages must have
been collected to represent any rolling 24-hour period.
Yesterday's 24-hour (Midnight to Midnight) PM10 averages are based on the
criteria that 18 or more hourly data points have been collected to make up the
average. If less than 18 hourly averages are collected then an “N/A” will
appear in yesterday’s 24-hour average for that instrument.
PM10 particles are less than or equal to 10 micrometers in diameter.
They tend to have a natural origin and are made of dust, dirt, and liquid droplets.
Sources of PM10 particles include dust stirred by wind and/or
vehicles traveling on unpaved roads, and crushing and grinding operations.
Nitrogen Dioxide (NO2)
A reddish brown, highly reactive gas forms when nitric oxide (NO) combines with oxygen in the atmosphere.
Once it has formed, nitrogen dioxide reacts with other pollutants. Eventually these reactions
result in the formation of ground-level ozone. The ppb (parts per billion)
values shown represent a 24-hour rolling average of hourly concentration data.
Ozone is a gas composed of three oxygen atoms.
It is not usually emitted directly into the air, but is created at ground level
by a chemical reaction between oxides of nitrogen (NOx)and volatile organic
compounds (VOC) in the presence of heat and sunlight. Ozone has the same
chemical structure whether it occurs miles above the earth or at ground level
and can be "good" or "bad," depending on its location in
the atmosphere. "Good" ozone occurs naturally in the stratosphere
(approximately 10 to 30 miles above the earth's surface) and forms a layer that
protects life on earth from the sun's harmful rays. In the earth's troposphere,
ground-level ozone is considered "bad."
VOC + NOx
+ Heat + Sunlight = Ozone
Temperature: The ambient air temperature measured in degrees Fahrenheit.
Relative Humidity: The ratio of water vapor in ambient air compared to the maximum amount of water
vapor that could occur at the ambient air temperature. The ratio is measured as a percent.
Wind Speed: Wind velocity measured in miles per hour.
Wind Direction: Wind direction is the direction from which the wind is blowing. It is measured using
a compass scale of 0 to 360 degrees. North is 0 or 360 degrees, East is 90
degrees, South is 180 degrees, and West is 270 degrees. See diagram.
Precipitation: Total amount of rainfall accumulated (measured) in inches per 24-hour period.
The Wyoming air quality monitoring instrumentation and its operation are designed to follow EPA
guidelines for monitoring, including:
40CFR50 National Primary and Secondary Ambient Air Quality Standards
Appendix D: Measurement Principle and Calibration Procedure for the measurement of Ozone
in the Atmosphere
Appendix F: Measurement Principal and Calibration Procedure for the measurement of
Nitrogen Dioxide in the Atmosphere
Appendix L: Reference Method for the Determination of Fine Particulate Matter as PM2.5
in the Atmosphere
Appendix M: Reference Method for the Determination of Particulate Matter as PM10 in the
All measurement devices and calibration standards will be traceable to the National
Institute of Standards and Technology (NIST).
40CFR53 Ambient Air Monitoring Reference and Equivalent Methods
40CFR58 Ambient Air Quality Surveillance
Appendix A: Quality Assurance Requirements for State and Local Air Monitoring Stations (SLAMS)
Appendix B: Quality Assurance Requirements for Prevention of Significant Deterioration (PSD) Air Monitoring
Appendix C: Ambient Air Quality Monitoring Methodology
Appendix E: Probe Siting Criteria for Ambient Air Quality Monitoring
EPA Quality Assurance Handbook for Air Pollution Measurement Systems:
Volume I, A Field Guide to Environmental Quality Assurance
Volume II: Ambient Air Quality Monitoring Program Quality System Development/Ambient Air Specific Methods
Volume IV, Meteorological Measurements
These guidelines establish quality assurance and quality control (QA/QC) standards
that provide data of known precision and accuracy.
Real-Time Data Disclaimer
Air quality information and meteorology data are displayed on this Web page typically within one to three
hours of their collection. As a result, data posted on the Live Sites Web page are raw data that have
not been validated by human review and may contain errors. Real-time data must be interpreted with
caution. These data are provided for public awareness and AQD review only. They
should not be used in any medical or scientific study.
Contact the Wyoming Department of Environmental Quality
to obtain quality-assured quarterly data summaries or access to
fully-validated raw data.