Pacific Southwest Research Station

Lake Tahoe visibility impairment source apportionment analysis

Principal Investigators:
Mark Green, Desert Research Institute
Antony Chen, Desert Research Institute
Dave Dubois, New Mexico State University
John Molenar, Air Resource Specialists, Inc.

Proposal [pdf]

Final Report [pdf]

Please contact Dr. Mark Green with questions regarding the report.

Project Summary

Atmospheric aerosols are solid or liquid particles suspended in the atmosphere. Aerosols affect atmospheric visibility by scattering light out of a sight path or by absorbing light and thus removing it from the sight path. A reasonable estimate of the contribution of each major aerosol component to haze (light extinction) can be made based on the mass concentration of each component and the relative humidity. The U.S. Environmental Protection Agency Regional Haze Regulations require the use of reconstructed light extinction from aerosol data to track trends in haze at mandatory Class I areas, such as the Desolation Wilderness area in the Lake Tahoe Basin.

The Desolation Wilderness area was designated a mandatory Class 1 area with visibility protection pursuant to the Clean Air Act Amendments of 1977. The Tahoe Regional Planning Authority (TRPA) established regional and sub-regional visibility thresholds in 1982, revised in 1999. Long-term monitoring conducted at Bliss State Park and South Lake Tahoe has found that the thresholds were met and visibility has improved since monitoring began. However, the TRPA 2006 Threshold Evaluation report noted concerns over backsliding, i.e. potential inability to maintain the improvements made in visual air quality.

This study interpreted 20 years of chemically speciated PM_2.5 aerosol data at Bliss State Park and 15 years-worth of data at South Lake Tahoe to determine the effects of light scattering and absorption by particles on visibility impairment in the Lake Tahoe Basin.