Relevance

This indicator measures sub-regional visibility in South Lake Tahoe and the distance that the human eye can see. It is measured by using a reconstructed light extinction (bext) value derived from an equation that combines measured concentrations of several gasses and particles. The equation is corrected for humidity and natural “background” light scattering. Bext is summarized by “average visibility days” (50th percentile values) and “worst visibility days” (90th percentile values) for each year followed by calculating the 3-year running average. This threshold standard has been adopted to protect sub-regional visibility and air quality.

Human and Environmental Drivers

Particulate matter in the atmosphere is the primary driver of visibility impairment because of the optical properties and long retention times in the air. The main sources of particulate matter in the basin are smoke and entrained roadway dust. Improving visibility trends are attributable to effective controls over motor vehicle, residential wood combustion, regulatory controls over prescribe burn days and road dust emissions. The most substantial risk to visibility is the increased frequency and intensity of wildfires in the Western U.S.

EIP Indicators

• 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.

• 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

• 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

• Regional Visibility Monitoring