This Factsheet: Oregon OSHA rules on smoke exposure includes a method for estimating air quality visually when local data is not available:
| AQI Index Values | Visibility: How Far You Can See |
|---|---|
| 0-50 | 15+ miles |
| 51-100 | 5-15 miles |
| 101-150 | 3-5 miles |
| 151-200 | 1-3 miles |
| 201-300 | 1 mile |
| 301+ | <1 mile |
This table draws on Oregon’s “5-3-1 Index” method for estimating air quality, which includes these instructions:
Determine the limit of your visual range by looking for distant targets or familiar landmarks such as mountains, mesas, hills, or buildings at known distances (miles). The visual range is that point at which these targets are no longer visible. As a general rule of thumb: if you can clearly see the outlines of individual trees on the horizon it is generally less than five miles away.
Ideally, the viewing of any distance targets should be made with the sun behind you. Looking into the sun or at an angle increases the ability of sunlight to reflect off of the smoke, and thus making the visibility estimate less reliable…