Air quality in South Lake Tahoe

How is the air quality in South Lake Tahoe, CA today?

Air quality in South Lake Tahoe varies in composition and severity depending on the season. Its highland climate features cold winters with regular snowfall and warm arid summers. Winters typically experience high particle pollution counts as a result of increased wood burning, building heating, and temperature inversions. Summers, on the other hand, tend to have low particle pollution but high ozone. Ozone is formed in the atmosphere from primary pollutants that exist at relatively constant levels. Sunlight and heat are required to force the reaction, however, and as a result, ozone only tends to accumulate in the hotter summer months.

The US Environmental Protection Agency (EPA) created the air quality index (AQI) scale to serve as a means for conveying a location’s overall air quality. AQI values are calculated by weighting six criteria pollutants for their risk to health in a formula. The highest individual AQI value dictates the overall AQI score, and the pollutant at the riskiest level becomes the “main pollutant.” Usually fine particulate matter (PM2.5) and ozone are the main pollutants responsible for determining overall AQI for their pervasiveness and high risk to human health.

In 2019, South Lake Tahoe averaged an annual AQI score of 21, meeting the “good” category threshold. The US EPA defines “good” air quality as air that poses little to no risk to health.

Despite such an optimistic annual average, short-term pollution spikes have caused South Lake Tahoe’s El Dorado County to fail to meet federal targets for 24-hour ozone and PM2.5 pollution.

Federal targets for short-term pollution spikes are based on a weighted 3-year average. Counties that average more than the allowable 3.2 unhealthy pollution days for each pollutant are considered “non-attainment” regions.

From 2016 to 2018, El Dorado County averaged 40.2 unhealthy ozone days a year, more than 12 times the federal target.¹ The greater Sacramento and Roseville area, which includes South Lake Tahoe, ranked 5th nationally for highest number of ozone days out of 228 surveyed metropolitan areas.

South Lake Tahoe’s warm, dry summers with little precipitation allow ozone to accumulate and be transported by wind from nearby cities. Carson city air pollution and Roseville air pollution are often culpable for affecting South Lake Tahoe’s own air quality, as they experience much hotter temperatures and higher ozone levels as a result.

While data from the same 2016 to 2018 monitoring period in El Dorado County lacked sufficient data availability for 24-hour PM2.5, the greater Sacramento-Roseville area in California serves as a rough indicator. On average, 11.3 days in this greater region are deemed as unhealthy PM2.5 days, landing the region 11^th for worst 24-hour particle pollution in the US out of 217 surveyed metropolitan areas.

In South Lake Tahoe, PM2.5 pollution is significantly higher in the winter months than in the summer months. In 2019, South Lake Tahoe’s most polluted months for PM2.5 were January, October, and December respectively. These seasonal PM2.5 pollution swings occur as a result of increased emissions from wood burning, building heating, and car idling as well as pollution-trapping weather events known as temperature inversions.

Temperature inversions occur when snow coverage creates a ground-level air layer colder than the air layer above it. The warm air layer acts like a lid, preventing the cooler air from dispersing in the atmosphere. During temperature inversions, South Lake Tahoe’s PM2.5 pollution accumulates until conditions change.

Is there smoke in South Lake Tahoe?

South Lake Tahoe smoke usually comes from wildfires burning in the late summer and early fall, or from domestic wood burning in the winter. Black carbon, or soot, is most of what we see and describe as smoke. In air pollution terms, black carbon and other microscopic particulates are grouped together as PM2.5, which is fine airborne matter measuring 2.5 micrograms or smaller.

PM2.5 pollution can remain suspended in the air for hours or even days, and is easily transported by wind. Follow live air pollution data for South Lake Tahoe at the top of this page and on the IQAir air pollution app to know when smoke in South Lake Tahoe has reached unhealthy levels.

Where is the fire in South Lake Tahoe?

Dry conditions and rising temperatures have exacerbated the frequency and severity of wildfires in South Lake Tahoe, California and further abroad, contributing to seasonal smoke in the region.

In 2020, there were a number of devastating fires in the South Lake Tahoe area, including the Numbers Fire that burned more than 18,000 acres, the Loyalton Fire that burned more than 47,000 acres, and the Slink fire that burned more than 12,000 acres.^2,3 The onslaught of fires in August 2020 contributed to a number of unhealthy air pollution days in South Lake Tahoe. On August 19th, South Lake Tahoe’s daily AQI reached 212, or “very unhealthy.” The drastic jump in short-term PM2.5 caused South Lake Tahoe to rank among the most polluted cities in the world on that day.

IQAir’s air quality map displays active fire data alongside live air quality data. Fire information is based on based satellite observations provided by NASA's Fire Information for Resource Management System (FIRMS), and is updated every 3 hours. Use the map to discover which fires may be contributing to South Lake Tahoe’s poor air quality.

How bad is the ozone in South Lake Tahoe?

South Lake Tahoe currently lacks city-based ozone measurements. As a result, inferences of the area’s ozone pollution are made from El Dorado County, to which South Lake Tahoe belongs. While hyperlocal differences are likely to exist, especially as a result of the areas significant micro-climates, El Dorado County’s severe non-attainment status for ozone is likely true for South Lake Tahoe as well.

In the 2016 to 2018 monitoring period, El Dorado County averaged 40.2 unhealthy ozone days. This high frequency landed the region 5th in the US for worst ozone pollution out of 228 included regions.

When will the smoke in South Lake Tahoe clear?

Weather is a key indicator for when air pollution in South Lake Tahoe will clear. Wind speed, wind direction, temperature, and inversion layers all play a significant role.

IQAir forecast air quality data uses artificial intelligence to crunch hundreds of millions data points in order to predict when smoke will clear out from South Lake Tahoe. The same method is used for thousands of global cities represented on the IQAir platform. For forecast air quality data, refer to the top of this page under the “Forecast” header.

While steps have been taken to ensure the accuracy of the forecast, there are limitations. Learn more about IQAir’s forecast method.

+ Article Resources

[1] American Lung Association. (2020). State of the air.
[2] Cal Fire. (2020). Loyalton fire.
[3] InciWeb: Incident Information System. (2020). Slink fire.