A firefighting air tanker drops retardant on the Caldor Fire over Grizzly Flats, Calif., on Tuesday. As of Friday, the wildfire has burned close to 70,000 acres. Photo by Peter DaSilva/UPI | License Photo
Aug. 20 -- Lake Tahoe has experienced "especially bad" air quality through the second half of this summer, and new data reveals the lake's air quality is at its worst levels of this decade.
The intense wildfire season California has experienced so far and the bowl-like geography surrounding Lake Tahoe that can cause pollutants to linger after getting trapped in the Sierra Nevada Mountain range, are partially responsible for the lake's poor air quality this year.
"The second half of summer has been especially bad for air quality around Lake Tahoe," AccuWeather Meteorologist Joe Curtis said. "The first half of summer was not as bad, but things rapidly deteriorated by late July and August."
According to AccuWeather Forecast Manager Bryan Sausman, summer tends to be the worst time for air quality due to less airflow. In addition, the wildfires throughout California have played a role.
The Caldor Fire, which is burning in El Dorado County directly southwest of Lake Tahoe, has so far torched close to 70,000 acres. As of Friday, the fire has been active for six days and is 0% contained.
On Tuesday, California Gov. Gavin Newsom declared a state of emergency for El Dorado County.
The sun sets on Tuesday behind the partially burned sign of the Walter Tyler Elementary School in Grizzly Flats, Calif., amid the the Caldor Fire. Photo by Peter DaSilva/UPI
"Any amount of smoke in the air will lead to poor air quality," Curtis said.
The Dixie Fire and Tamarack Fire, both of which erupted near Lake Tahoe in Northern California this summer, have also played a role in the dwindling air quality of the lake. The Tamarack Fire has burned over 68,000 acres so far and is more than 82% contained as of Friday while the massive Dixie Fire remains just 35% contained with more than 700,000 acres already burned.
"It's been bad in the past, it's bad now and it will be bad again in the future," Dave Johnston, air pollution control officer for the El Dorado County Air Quality Management District, told The San Francisco Chronicle.
"Lake Tahoe is in a basin surrounded by mountains, so it is difficult for smoke to dissipate without some wind behind it."
This year's air pollution at Lake Tahoe has been much higher than in previous years.
A firefighting tanker drops retardant on the Caldor Fire over Grizzly Flats, Calif., on Tuesday. Photo by Peter DaSilva/UPI
One way of measuring pollution is through particulate matter. According to the California Air Resources Board, particulate matter is an airborne mixture of chemicals. Most of pm 2.5 is made up of emissions coming from the combustion of gasoline, oil, diesel fuel and wood, and it gets its name from being less than 2.5 microns in diameter.
In 2020, data from the board reveals that Lake Tahoe's air basin had an average level of 5.3 pm 2.5 between June 1 and Aug. 17. The year prior, the basin had an average level of 1.1 pm 2.5 during the same time frame.
The air basin reported an average level of 18 pm 2.5 so far in 2021 -- higher than any other year of this decade within the time frame of June 1 to Aug. 17.
Particulate matter can reduce visibility by affecting the way light is absorbed in the atmosphere and cause negative impacts to the climate and ecosystem when it deposits into water sources, also affecting water quality and clarity.
On Thursday, Lake Tahoe was experiencing "pretty good" air quality however, with the presence of the Caldor fire just 40 miles away, the good air quality is not expected to last long, Curtis said. He added that forecasters are able to predict changes in air quality by observing changes in wind direction and patterns.
Trees catch fire after flames from the Caldor Fire jumped the Mormon Emigrant Trail in Happy Valley, Calif., on Tuesday. Photo by Peter DaSilva/UPI
"Anyone visiting the area should take advantage of the nice weather and relatively clean air while it lasts because more smoke and haze will fill the atmosphere again by Friday," he said. "Winds will shift out of the west-southwest Saturday afternoon, which will allow smoke particles from distant wildfires to drift toward Lake Tahoe."
According to Curtis, individuals with underlying respiratory or cardiovascular conditions are at a bigger risk of being affected by poor air quality. He recommended that those who have underlying conditions avoid strenuous outdoor activity when the atmosphere is filled with smoke.
"The best thing to do is to stay inside as much as possible. Using an air filter inside the home will also be helpful because it continuously works to clean the air," he said.