The Ventilation Index (VI) is a term used in air pollution meteorology. It is also known as the venting index. The Ventilation 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 ventilation indexes (usually from a computer model) are available for 26 different areas of the province. Stronger wind
speeds and thicker mixed layers will produce higher ventilation indexes. 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:
Ventilation 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.
Environment Canada's Smoke Control Forecast contains information on the forecast Ventilation Index and the upper winds in the surface mixed layer. 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.
In the Ministry of Environment's version of the Smoke Control Forecast, archived smoke-control forecasts for the last several years are also provided.
Top