Sub-Regional Visibility 90th Percentile ("Worst Visibility Days")
This indicator measures visibility on low visibility days in the urbanized area of South Lake Tahoe. Visibility measures the distance at which an object or light can be clearly discerned by the human eye. Sources of locally generated haze pollutants include entrained/suspended roadway particles, vehicle emissions, residential wood burning, campfires, prescribed fires, and wildfires. Decreases in visibility on the worst days is largely attributed to smoke from wildfires.Some particles responsible for the degradation of regional visibility in the Tahoe Basin include dust and other pollutants transported into the Basin from areas as far as Asia. Regional programs such as increased street sweeping and work to improve forest health aim to increase sub-regional visibility. Sub-regional visibility is monitored at Lake Tahoe Community College as part of the national IMPROVE monitoring network.
Status
Sub-regional visibility conditions at the old South Lake Tahoe site and current Lake Tahoe Community College site.
Evaluation Map
Sub-regional visibility monitoring station at the Lake Tahoe Community College.
2019 Evaluation
- Status
- Considerably Better Than Target
- Trend
- Insufficient Data to Determine Trend
- Confidence
- Moderate
Applicable Standard
AQ8: Achieve an extinction coefficient of 125 Mm-1 at least 90 percent of the time as calculated from aerosol species concentrations measured at the South Lake Tahoe monitoring site (visual range of 31 km, 19 miles).
Key Points
- The South Lake Tahoe monitoring station was recently re-established. Compared to data from the 1990s, sub-regional visibility appears to have greatly improved.
- Visibility on average days in the urbanized area of South Lake Tahoe is well within air quality standards.
- Decreases in visibility on the worst days are largely attributed to smoke from severe wildfires. While the fires were bad at the times, there were not enough worst days to offset the good days.
Delivering and Measuring Success
EIP Indicators
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Miles of Street Sweeping
Since 2009 EIP partners have swept more than 61,000 miles of roadways within the Tahoe Basin reducing fine sediment particles from roadways entering the air and water.
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Non-Compliant Wood Stoves Removed or Retrofitted
This EIP performance measure tracks removal of polluting wood stoves to reduce local air pollution for human and ecosystem health.
Example EIP Projects
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Purchase of High-Efficiency Sweepers - City of South Lake Tahoe
To help increase sub-regional visibility, programs have been put in place for increased street sweeping such as the purchase of high-efficiency street sweepers.
Monitoring Programs