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.

Pollutant Data

Particulate (PM10)
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 (O3)
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

Meteorological Data

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.

Quality Assurance