LAKE TAHOE BASIN “-It’s like they say, “What happens in Vegas, stays in Vegas.”

The same is true for pollutants in the Tahoe Basin, says Thomas Cahill, the air quality expert for the Environmental Protection Agency’s Region 9 Sierra Nevada Public Land Management Association, and member of the University of California at Davis “Delta Group” that regularly audits Tahoe’s most challenging environmental issues.

During the winter months, an inversion layer traps a pocket of warm air in valley areas where the air contracts and creates a lower ceiling keeping pollutants from escaping the alpine ranges. Winter aerosols include wood smoke, sand transport, industrial and transportation-related emissions, and even Dust from Asia.

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But nitrogen oxides, a greenhouse gas and precursor to hazardous ozone, are increasing in the summer, Cahill said, emitted from the tail pipes of traffic along Interstate 80.

“We’re thinking this is because of the increased truck traffic. Nitrous oxides are really only produced at that level by trains and trucks, and much less so with cars. The use of 87 octane was a major victory toward cleaner emissions for automobiles,” Cahill said, explaining that diesel fuel is “inherently dirty.”

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Nitrogen oxides combine with hydrocarbons naturally released from plant life in the presence of ultra-violet light from the sun, said Joe Fish, deputy air pollution control officer for the Sierra Air Quality Management District, making ozone, which becomes unhealthy for humans at one part per million.

The entire Basin does meet national ozone standards, and will also meet the new standards revised by the Environmental Protection Agency in 2008, Placer County Air Pollution Control District reports. In comparison, places like Auburn and Colfax do not meet these standards.

The Sierra Nevada Ecosystem Project, funded by the U.S. Forest Service, reports that during the winter, the Tahoe Basin receives its worst concentration of ozone, sulfates, nitrates and other fine particles from the Central Valley in California, creating multiple health and environmental issues. Placer County says summer time pollutants could be worse due to boats, as well as the natural release of airborne particles from forests during the summer.

California currently does not meet national emission standards for ozone and nitrates and state analysis demonstrate high concentrations of these pollutants just north east of Sacramento.

However, Tahoe can’t claim victim; in fact, local pollution, primarily from car exhaust, is more often the culprit.

While some pollutants are imported by air masses flowing east of major urban areas like Sacramento and San Francisco, it is generally thought that the majority of the pollution comes from within the basin, though the exact ratio remains unclear.

For instance, the Ecosystem Project reports, “The low concentration of transported nitrates, and their small particulate size, must be contrasted with the high levels of local nitrates from the highways that ring the lake.”

In addition, highway road dust from the sanding and salting of frequent basin sources, as well as imported fine particles transported across the Pacific called “Asian dust values,” are becoming an increasingly significant source of decreased visibility.

Asian dust contributes up to a ton of micro-particles per year to Tahoe. Speculation exists as to whether or not the increased dirt and dust in the air will contribute to increased melting and greater snowpack lost. Whether or not this would effect the Tahoe’s diminishing snowpack, Cahill remarked, “is beyond what I know. And I’ve been doing this for 40 years.”

“Asian dust values are not a big deal for Tahoe, but on a global scale it increases global warming,” Cahill said. “Sierra dust cools the Earth because it is a scattering aerosol which reflects sunlight, but Asian dust is coated with soot and sulfates, trapping radiation.”

Fires also contribute to pollution values ” worldwide and locally. Though not normally understood as a primary source of pollution, burning wood has had a big impact on the air-quality, lake and water visibility, and area tax hikes, as well as contributing to overall carbon dioxide production in the region.

“The State of the Lake Report,” conducted by the University of California at Davis in 2007, states “neighborhood residential wood-burning is a continuous source of localized air pollution. Most wood heaters (woodstoves and fireplaces) release far more air pollution, indoors and out, than heaters using other fuels (such as natural gas).”

Each year the Tahoe Regional Planning Agency receives federal funding for burning between 6,000-9,000 acres to imitate low-intensity fires in 2,000-8,000 acres of the Tahoe region. “Prescribed fire is the best way to mimic natural low-intensity fires and reduce the chances of wildfires,” said Ann Westling Public Affairs Officer for the Tahoe National Forest.

Proscribed fires reduce understory, trim away canopy that blocks growth in other areas, and increases the richness in the sub-alpine soil, which is considered to be nutrient-poor.

The costs to the taxpayer over the last 20 years has totaled over 25 million federally, and 4 million locally.

According to the Tahoe Regional Planning Association, “large fires devastate lake clarity.”

However, the Angora Fire in 2006 added between 2.5- and 7-times the normal rate of wood burning, and the overall contribution to the lake was decided to be negligible at only about 1 to 2 percent of the background levels.

As far back as 1969, and as a result of the developing seriousness of California’s low air quality, the state began establishing high standards for air quality, “sufficient to reduce visibility to less than 10 miles when relative humidity is less than 70 percent,” according to the California Environmental Protection Agency.