Inversions

Rapid City Air Pollution Alert for Inversions

Area of impact: Citywide which includes the three miles surrounding the city limits.

Meteorological Criteria: The following weather conditions need to exist for a 12-hour period before an air quality advisory will be called:

• The forecasted low temperature needs to be 20 degrees Fahrenheit or less;
• The forecasted daily average wind speed needs to be 8 mph or less;
• The forecasted inversion layer needs to be less than 4500 feet; and
• No precipitation or fog is forecasted.

The air pollution advisory will be discontinued when the following weather conditions exist:

• The PM10 concentrations are below 150 ug/m³ for a 3 hour average; or
• There is greater than 0.02 inches of precipitation.

Air Pollution Advisory issuance protocol : An air pollution advisory is issued when conditions exist for poor air quality. The National Weather Service issues the advisory to the Department of Environment and Natural Resources and Rapid City Air Quality staff to begin review of PM10 air quality data. The National Weather Service contacts the Department of Environment and Natural Resources. The first Department of Environment and Natural Resources contact is Brad Schultz in Pierre at 773-3151 then Jon Epp in Rapid City at 394-2229. The Rapid City air quality staff at 394-4120 is contacted next if no one is available at the Department of Environment and Natural Resources.  The Department of Environment and Natural Resources contacts the industry sources to limit activities during the air pollution alert.

Air Pollution Alerts issuance protocol: An air pollution alert is called when PM10 ambient air quality concentrations exceed 200 ug/m³ over a three hour average. These concentrations are continuously observed during the advisory and alert. The Department of Environment and Natural Resources contacts the National Weather Service to issue an air pollution alert based upon the PM10 data. The most recent air pollution alert can be viewed at the National Weather Service website.  The Department of Environment and Natural Resources or the Rapid CIty air quality staff contacts the National Weather Service to discontinue the alert based upon the PM10 data. 

Precautions: The following precautions should be taken during any of these situations:
Elderly citizens, young children and individuals with respiratory problems should avoid excessive physical exertion and minimize outdoor activities. Although these people are the most susceptible to health impacts, it is recommended that everyone take precautions to avoid being exposed to these poor air quality conditions.

Voluntary actions to reduce air pollution levels: It is requested that all residents discontinue operation of wood or coal home heating devices, unless it is the sole source of heat. To further reduce air pollution levels, it is requested that construction, industrial or agricultural activities that generate air pollution cease operation, minimize the activity, or use additional preventative measures during the alert.

Basis for criteria selection: An air inversion is created when the air close to the surface of the earth is colder than the air above it. For the Rapid City area, air pollution levels have been observed to increase when an inversion upper air layer is lower than 4500 feet, average hourly surface wind speeds are less than 8 miles per hour, and surface temperatures are below 20 degrees Fahrenheit and there is no precipitation or fog present. The suspended dust and smoke from air pollution sources become trapped in the dense stagnant cold air near the surface of the earth. Air pollution levels typically increase with the intensity and duration of the inversion. There are three ways for an inversion to be eliminated. It takes an incoming weather front to create good air dispersion conditions for the pollution to be released from the lower atmosphere, strong winds to push the air pollution out of the area, or measurable precipitation ( more than 0.02 inches) to wash the pollution out of the air.

The following are activities that contribute to elevated air pollution levels:

• Residential fuel burning - fireplaces, woodstoves, pellet stoves and coal burning stoves;
• Industrial activity - coal burning kilns, furnaces, boilers and normal day-to-day activities;
• Construction activity;
• Automobile exhaust; and
• Reentrained dust - street sanding material and dust deposited on public streets that is suspended into the air from vehicular traffic.