Final Mitigated Negative Declaration and Response to Comments

III.
AIR QUALITY.
ENVIRONMENTAL SETTING
Lake Tahoe sits in a high-elevation basin bounded by the Sierra Nevada Mountains to the west
and the Carson Range to the east. The source of the air pollutants that threaten Lake Tahoe
water clarity are created both locally and from outside the basin. Local sources are the most
significant contributor of pollutants and include urban and forest wood smoke, vehicle exhaust,
and dust (Gertler et al. 2006). Air pollution sources from outside the basin include Sacramento
and San Francisco Bay Area urban pollutants and smoke from wildfires.
The Lake Tahoe Air Basin is comprised of the eastern portions of Placer and El Dorado
Counties in California and the western portions of Washoe, Douglas, and Carson City Counties
in Nevada that encompass the Lake Tahoe hydrographic basin (CARB 2008). Emerald Bay
State Park (SP) is within the jurisdiction of the El Dorado County Air Quality Management
District (EDCAQMD 2010).
Climate
The climate of the Lake Tahoe region is generally Mediterranean, but is modified by
topography and geography. It is characterized by relatively warm, dry summers, interrupted by
occasional lightning storms, and cold, wet winters with variable precipitation, mostly falling as
snow (O’Hara et al. 2007). Weather conditions can change rapidly as upper level wind
currents and pressure systems in the western states shift locations and both dry and wet
frontal systems move through the mountainous terrain.
The topographic condition of the Lake Tahoe Basin surrounded by high mountains has a
tremendous influence on local weather conditions and the resulting air quality. Lake Tahoe
experiences both surface-based and subsidence inversions. Surface-based inversions form
when cool air settles down into the basin replacing the warmer surface air, resulting in the
warm air rising and creating a lid over the basin, which traps the air below. These surfacebased
inversions generally begin late evening and lift during mid-morning as the sun warms
the atmosphere. Subsidence inversions result from high pressure centered over the region.
The high pressure compresses the atmosphere, creating a lid over the basin. These high
pressure systems are common during the summer and fall, and may persist for long periods.
Air Quality Designations
Public land owners and managers within El Dorado County are subject to air quality planning
programs required by the federal Clean Air Act of 1970 (CAA), its 1990 amendments, and the
California Clean Air Act of 1988 (CCAA). Both the federal and state clean air statutes provide
for ambient air quality standards related to air pollutants, timetables for progressing toward
achieving and maintaining ambient standards, and the development of plans to guide air
quality improvement efforts by state and local agencies. Ambient air pollutants called criteria
pollutants are pollutants for which acceptable levels of exposure can be determined and for
which an ambient air quality standard has been set.
The United States Environmental Protection Agency (USEPA) is responsible for setting
National Ambient Air Quality Standards (NAAQS) and established national area designations
Asian Clam Control Project IS/MND
Emerald Bay State Park
California Department of Parks and Recreation
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