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Annual Average PM2.5 Concentration

PM2.5 is very fine particulate matter, 2.5 micrometers and smaller. This indicator measures the annual average PM2.5 concentration for the calendar year. Particulate matter less than or equal to 2.5 microns in size (PM2.5) is associated with a variety of human health concerns, including asthma, lung diseases, and heart disease. The primary sources of PM2.5 in the Tahoe Basin are residential fuel combustion, campfires, wildfires, prescribed fires, motor vehicles, and dust from unpaved roads. PM2.5 is monitored by TRPA and partners at three sites around the Basin.

Annual Average Pm2.5 Concentration.jpg

Status

3-year rolling annual average PM2.5 in the Tahoe Region from 1991 to present. 

Data provided by the Desert Research Institute. Access detailed datasets on Tahoe Open Data, including:: Air Quality Station Location Data. Daily Monitoring Data. Yearly Average Data.

Evaluation Map

The location of all air quality monitoring stations in the Lake Tahoe Basin. PM2.5 is monitored by TRPA and partners at three of these locations.

2023 Evaluation

Status
Considerably Better Than Target
Trend
Little or No Change
Confidence
Moderate
View Evaluation

Applicable Standard

AQ12: Particulate Matter2.5 Annual Arithmetic Average - Maintain Particulate Matter2.5 at or below annual arithmetic average of 12µg/m3 in the portion of the Region within California and maintain Particulate Matter2.5 at or below annual arithmetic average of 15µg/m3 in the portion of the Region within Nevada. Particulate Matter2.5 measurements shall be made using gravimetric or beta attenuation methods or any equivalent procedure which can be shown to provide equivalent results at or near the level of air quality standard.

Key Points

  • Average PM2.5 concentrations are well within air quality standards except for 2021 during the Caldor fire. 
  • Available data suggest that PM2.5 levels in Tahoe have decreased since the early 1990’s, but monitoring was not continuous.
  • Lake Tahoe experiences long-term improvement in the average annual concentrations of particulate matter, but an increase in peak concentrations of particulate matter.
  • The best scenario for air quality on a local, regional, and national scale is the restoration of the natural fire cycle through prescribed fire or managing natural ignitions when conditions are favorable (Schweizer et al. 2019)
  • In 2024, the US EPA revised the Particulate Matter (PM) National Ambient Air Quality Standards (NAAQS) for PM2.5 to 9.0 µg/m3 Annual arithmetic mean, averaged over 3 years.  

About the Threshold

This indicator addresses annual average PM2.5 concentrations in the Lake Tahoe Region. Particulate matter less than or equal to 2.5 microns in size (PM2.5) is extremely small and can be inhaled deep into the lungs, causing or aggravating asthma, lung diseases, and heart disease. Some particles pass into the bloodstream and some are considered carcinogens. Federal and state standards have been adopted to protect human health.
The primary sources of PM2.5 in the Lake Tahoe Region are residential fuel combustion, wood smoke from wildfires and prescribed fires, motor vehicles and paved and unpaved road dust. PM2.5 results from both primary emissions (PM2.5 directly emitted from sources) and from secondary formation from reactions of gases in the atmosphere. Small particles are also transported into the Lake Tahoe Region, and the ambient concentration of PM2.5 is highly dependent on meteorological conditions such as wind speed, and mixing conditions.

Delivering and Measuring Success

EIP Action Priorities

  • Build and Enhance Trail Networks

    Bicycling, walking, and other forms of active transportation are important methods of travel that promote healthy lifestyles, improve air quality.

  • Build and Enhance Transit Systems

    Comprehensive and coordinated bus and shuttle transit system that provides seamless around the lake service.

  • Implement Prescribed Fire

    Prescribed fire and fire used for ecological benefit can reduce smoke exposure from large high intensity fires.

  • Reduce Hazardous Fuels

    Reduce hazardous fuels and proactively manage forests to improve ecosystem resilience and reduce wildfire smoke.

EIP Indicators

Example EIP Projects

  • Street Sweeper Purchase

    Reductions in particulate matter on the South Shore can mostly be attributed to reductions in local sources such as increased street sweeping.

Local and Regional Plans

Monitoring Programs

Rationale Details

Considerably Better Than Target. The status is determined on the average of the 3-year averages for the monitoring period 2020-2023 for all monitoring locations. The average reading is 5.7 ppm, 62% of the allowable value, 9 µg/m3. Therefore, the current status is considerably better than target.
Little or No Change. Trend was determined using the annual average reading at various South Lake Tahoe sites from 1989-2023 using the Theil-Sen robust regression method. An annual decrease of -.33% was observed during the time frame. Therefore, a trend of little or no change was determined.

Confidence Details

High. Monitoring was conducted using strict protocols to collect a long-term, high quality dataset.
Low. Confidence of trend is based on the coefficient of determination and t-test significance. R²=0.0196 (low), p-value= 0.3322.
Moderate. If one confidence rating is high and the other is low, the overall confidence rating is moderate.

Additional Figures and Resources

No photos available.

No documents available.