Because of wildfires in North Central California (typically in August and September) Tahoe can be have a lot of smoke in the air. Depending on wind direction it can vary from day to day.
Smoke is just 1 type of pollution that affects air quality, but it becomes the major one during these fires. The affect on health and the environment is measured by the Air Quality Index (AQI).
See Air Quality Index at donsnotes.com
Air Quality maps:
Purple Air You have to wait for it to zoom in.
IQAir (AirVisual) has a forecast.
The AirVisual (IQAir) App is good
AirNow | EPA
Westshore Cafe Web-Cam
North Central California Fires