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Urban smog from Central Valley plagues Mammoth

June 12, 2014

The hazy skies seen most afternoons for the past several weeks, like the one above Mammoth on June 10, are caused by air pollution from the Central Valley. Photo/Wendilyn Grasseschi

Urban smog isn’t one of those things most people associate with Mammoth, but that is the likely source of the persistent silver-gray hazy air residents have been breathing almost every afternoon and evening since the day after Memorial Day.

The thick haze that has descended on the Mammoth area starting at about 4 p.m. each day and lasting until midnight comes courtesy of the Central Valley. There, automobile exhaust and other air pollutants have combined with unseasonably hot weather to create both invisible ozone pollution and visible smog, according to local air pollution control district officer Ted Schade.

Mammoth (along with an area from about Tioga Pass to Aspen Springs) has been hardest hit for the same reasons it is hardest hit in the winter with snow—because of the low gap in the Sierra crest, called Mammoth Pass.

“The same things that bring you your snow in the winter are likely bringing in this haze,” Schade said, noting that although instruments cannot identify the haze completely, there is no other source that he can identify.

“My wife calls it ‘schmutz,’” he said.

Mammoth and areas nearby are experiencing the worst air quality in the whole Great Basin Unified Air Pollution Control District, which stretches from southern Inyo County to the Nevada border, he said.

“This is a pattern typically associated with ozone pollution,” he said. “The sun bakes emissions from the tail pipes of cars and converts some of it to ozone, then it travels over the pass. That’s also why it’s been so much worse in the later afternoons. When it’s been reaching the 90s in Bishop, it’s got to be above 100 over there, and the temperatures increase during the late afternoon.”

Another factor trapping the pollution in the region is a relatively stagnant air pattern that has been in place for much of the last two weeks, with the exception of this week’s rain storm.

In other words, there has been almost no significant weather in the past few weeks, nothing to flush the pollution out of the area or tamp it down in the Central Valley.

The air pollution is not considered dangerous to human health, especially compared to true urban smog, Schade said, because it is at relatively low concentrations.

It might be something, however, Eastern Sierra residents will have to get used to, or at least, expect at greater frequencies, according to Dr. Thomas Painter, a Jet Propulsion Laboratory research scientist who recently spoke at one of the Green Church lectures sponsored by the Sierra Nevada Aquatic Research Laboratory (SNARL).

During his talk, an audience member asked Painter whether the Gobi Desert dust that has also impaired air quality in the Eastern Sierra this spring (for more than a week in April) might play a part in increasing the rate at which the Sierra snowpack was melting (dust collects on snow, which then traps more heat than pure white snow since dust is darker than snow).

Painter said the research on that was not clear, but he indicated that preliminary research points toward another possible source of a dust layer that scientists are finding—the Central Valley.

“We are beginning to think that’s where this dust layer is coming from,” he said, adding that new technologies to measure and identify the source of the dust will soon be implemented so the hypothesis can be tested.

At that time, he noted the ongoing drought might also be a contributing factor to the increased dust on the snow, since there was less irrigation in the Central Valley and thus, more dust.

The same patterns bringing the dust could also be bringing other air pollution across the Sierra, he said.

Schade said a new system to measure and source air pollution will be implemented before the end of this year, at UC Los Angeles’ Bishop-based White Mountain Research Center.

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