When using the visibility index to determine smoke concentrations, it is important to:
- Face away from the sun.
- Determine the limit of your visibility range by looking for targets at known distances (miles). The visible range is the point at which even high-contrast objects (e.g., a dark forested mountain viewed against the sky at noon) totally disappear.
- At times, the visibility index may be hard to use, especially if specific landmarks at known distances are not available for judging visibility range, or at dawn or dusk. Furthermore, the above visibility categories for PM levels only apply in dry air conditions. For a given PM level, visibility decreases substantially at relative humidity above 65%, therefore, this method of estimation should not be used under conditions of high humidity. At night or during periods when visibility cannot be used to estimate smoke levels, intense smoky odor can be used to indicate potentially harmful levels.
For additional information and updates, you may visit the Air Quality Management District Wildfire Smoke Webpage at https://www.co.shasta.ca.us/index/drm_index/aq_index/aq_wildfire.aspx or call 225-5674.