B.C. Air Quality

Ventilation Index

The Ventilation Index is a term used in air pollution meteorology. (It is also known as the Venting Index.) The index is a numerical value related to the potential of the atmosphere to disperse airborne pollutants, such as smoke from a prescribed fire. It is based on both the current wind speed in the mixed layer and the mixing height. The mixed layer is the surface layer of air that is turbulent and well mixed. The mixing height is the thickness (sometimes zero) of this mixed layer.

Forecast venting indices (usually from a computer model) are available for 26 different areas of the province. Stronger wind speeds and thicker mixed layers will produce higher venting indices. For convenience, the Ventilation Index is converted to a scale of 0 to 100. On this scale, the capacity of the atmosphere to disperse pollutants is related to the following Ventilation Index values:

Venting Index

Ventilation Category

0 - 33

POOR ventilation

34 - 54

FAIR ventilation

55 - 100

GOOD ventilation


These category boundaries differ in some jurisdictions. For example, in the Regional District of Central Okanagan, the range of the "GOOD" ventilation category is currently 65 to 100. A ventilation index of 0 implies no ability of the atmosphere to disperse pollutants (smoke), while a value of 100 implies an excellent dispersion ability.

Use of the Ventilation Index

The Ministry of Environment's Ventilation Index (also available by phoning 1-888-281-2992) contains smoke-control forecasts for the current and following day, as well as archived smoke-control forecasts for the last several years. If the Ventilation Index indicates POOR or FAIR, then smoke that results from burning will tend to build up, causing air pollution. To avoid such pollution, outdoor burning is restricted when the index is POOR or FAIR.

Contact your regional Ministry of Environment office for more details.

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