Monitoring Data >> Current Data by Monitor >> Meteorological Parameters
Meteorological Parameters
Meteorological Measurements
  • Temperature: The ambient air temperature reported in degrees Fahrenheit. To convert to Celsius, subtract 32 from degrees Fahrenheit and divide by 1.8. Temperature sensors are often mounted on a lightweight tower at either 2 meters (2m) or 10 meters (10m) above the ground surface.
  • Relative Humidity: The ratio of actual water vapor in the ambient air to the maximum amount that could occur at the same ambient air temperature. The ratio is reported as a percentage.

  • Precipitation: Amount of rainfall reported in inches per hour.

  • Wind Speed: Wind velocity is reported in miles per hour. To convert to meters per second, divide by 2.24.

  • Wind Direction: Wind Directions Wind direction is the cardinal or intercardinal direction from which the wind is blowing. Wind directions are also reported in degrees azimuth, a compass scale of 0° to 360°. The cardinal directions are North (0° or 360° azimuth), East (90°), South (180°) and West (270°). See diagram at left.

  • Solar Radiation: The amount of atmospheric solar radiation with a wavelength of 0.4 to 1.1 micrometers in length reported in watts per square meter. These wavelengths are in the infrared and the visible light range of the electromagnetic spectrum.

Pollutant Concentration Measurements
Two categories of air pollutants are monitored and shown here: Suspended Particulates and Gaseous Pollutants. Suspended particulates are generally measured and reported in units of micrograms per cubic meter (µg/m3). Gaseous pollutants are reported in either parts per billion (ppb) or parts per million (ppm), depending on the numerical precision required and the sensitivity of the monitoring equipment. All pollutants are shown as one-hour averages, except as noted below.

Note 1:
The 24-hour standard for PM2.5 is required to be evaluated using specially designated monitors termed "federal reference method (abbreviated "FRM") or federal equivalent method" ("FEM") monitors, FRM monitors currently are not capable of reporting one-hour averages and are not available for real-time reports. For real-time reports, we acquire PM2.5 one-hour averages using either a "tapered element oscillating microbalance" instrument ("TEOM") or a beta attenuation method instrument ("BAM").

Each TEOM is paired with an FRM at the same monitoring station, and we periodically compare 24-hour averages calculated from the TEOM data to the corresponding 24-hour averages measured directly by its companion FRM. BAM monitors are operable in a configuration that is FEM, but we pair new ones similarly with an FRM for a probationary period (typically, 12 months), and where there is a TEOM collocated with a BAM, we use the TEOM data for real-time reports. For reporting purposes, TEOM averages are adjusted in a manner explained in the next paragraph.

There is a strong, though imperfect, linear relationship between the TEOM and FRM data. Once we have accumulated at least 12 months of paired averages at a site, we can estimate that relationship using inverse regression and use it to compute "FRM-adjusted" TEOM averages representing our best prediction of the one-hour averages that would have been reported by a FRM. The regression equation can be stored in the TEOM's datalogger so that FRM-adjusted one-hour averages are computed in real time. We use the FRM-adjusted averages in online real-time data reports and current Air Quality Index reports. In general, the TEOM-FRM relationship varies with each season of the year, so at most sites, we cycle annually through 4 different regression equations.