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Home Air Criteria Pollutants

PM 2.5 Annual Average Concentration

Status and Trend

Interpretation and Commentary


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Status: At or Somewhat Better Than Target
Trend: Litle or No Change
Confidence: Moderate

  • Relevance - 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.
  • Adopted Standards - California: 12 mg/m3 annual concentration must not be exceeded; Federal: 15 mg/m3, 3-year average of weighted annual mean concentration must not be exceeded (not reported here); TRPA: no adopted standard; Nevada: No adopted standard.
  • Indicator - Annual average PM2.5 concentrations at any permanent monitoring station (mg/m3).
  • Status – The 2009 annual average PM2.5 concentration measured at Bliss State Park is 2.92 µg/m3 (IMPROVE 2011). The 2009 annual average value is 75.7% below the most stringent California standard of 12 µg/m3, resulting in a status determination of “at or somewhat better than target,” because the most current measured value is within 25% of the standard (24.3% of standard).
  • Trend – Trends were calculated using the Thiel regression method which is academically well accepted for air quality analysis.
    • Long Term Trends - The long-term trends for South Lake Tahoe (1991 to 2003) and Bliss State Park (1991-2009) were decreasing in annual average PM2.5 concentrations. Trend at the Bliss site is decreasing at a rate of -0.02 µg/m3 /yr, or -0.2% per year relative to the most stringent California standard of 12 µg/m3. The trend at the South Lake Tahoe monitoring site was decreasing at a more rapid rate of -0.25 µg/m3 /year, or -2.1%/year of the California standard. Because current data are insufficient (2004 to 2010) for the South Lake Tahoe Site, the Bliss site was used to characterize the regional annual average PM2.5 concentration trend of “little or no change.”
    • 5 Year Trend - The 5-year trend for the last 5 years (2005-2009) at Bliss State Park indicates an increase in annual average PM2.5 concentration at a rate of +0.30 µg/m3 /yr., or +2.5% of the standard per year. Note that short-term trends in air quality are typically not reliable due to high inter-annual indicator variability, variability in meteorology and the small number of points evaluated (n=5).

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  • Confidence
    • Status - There is “high” confidence in the status determination. IMPROVE samplers collected data at both monitoring sites, and used the IMPROVE sampling protocol which is not a Federal Reference Method (FRM) PM2.5 sampler, but is accepted for determining compliance with regional haze regulations. Consistent data from 1993 through 2009 are available for the Bliss State Park site. However, insufficient data have been collected in the past 6 years for the City of South Lake Tahoe site. There was extensive testing of the samplers, and rigorous quality control procedures employed at the measurement laboratories.
    • Long Term Trends - The confidence in the long-term trend at Bliss State Park for the analysis of 17 data points of the annual average PM2.5 concentration is “moderate,” with a confidence level of 83%, an S = -24, and a P = 0.17. The confidence in the long- term trend for the South Lake Tahoe site of 15 data points is high with a confidence level of 100%, a S=-59 and a P < 0.01.
    • 5 Year Trend - The confidence in the trend for the most recent 5 years (2005-2009) at Bliss State Park is moderate with a confidence level of 88%, an S = 6, and a P = 0.12.
    •  Overall Confidence - The overall confidence in the status and trend is “moderate” because of the “moderate” confidence assigned to the trend recorded at the Bliss monitoring.
  • Human and Environmental Drivers - The primary sources of PM2.5 in the Lake Tahoe Basin 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 (e.g. sulfate particles from sulfur dioxide emissions and reactions with other gases, nitrate particles from emissions mainly of nitrogen oxide and reactions with other gases such as ammonia), and condensation of semi-volatile organic gases. Small particles are also transported into the Lake Tahoe Basin from distant locations, and the ambient concentration of PM2.5 is highly dependent on meteorological conditions such as wind speed, and mixing conditions.
  • Monitoring Approach – PM2.5 is currently monitored at one site in the Lake Tahoe Basin (Bliss State Park). This site is expected to be representative of background levels of PM2.5 transported into the Lake Tahoe Basin and has been in operation since 1990. Historical data (1989-2004) are available for South Lake Tahoe. The South Lake Tahoe site is expected to represent basin-wide highest PM2.5 concentrations because it is located in a relatively densely populated urban area. These sites used the IMPROVE sampler, which is not a Federal Reference Method PM2.5 sampler but is accepted for determining compliance with regional haze regulations.
  • Monitoring Partners–  Interagency Monitoring of Protected Visual Environments (IMPROVE), Tahoe Regional Planning Agency

Links

 
  • Monitoring Plan
  • Conceptual Model

Map

PM2.5 Monitoring Locations in the Lake Tahoe Basin

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Trend Charts

 
The annual average concentrations of particulate matter less than or equal to 2.5 microns in size (PM2.5) measured at Bliss State Park and South Lake Tahoe monitoring sites. Current concentrations are considerably better than federal and California standards. The long-term trend at each site shows decreasing annual average concentrations of PM2.5
Source: U.S. Environmental Protection Agency, Air Data
Nevada Division of Environmental Protection

Additional Info

References

  1. IMPROVE data: http://views.cira.colostate.edu/web/.
  2. Tahoe Regional Planning Agency visibility data.

Additional Information

  1. PM2.5 24 hr Indicator
  2. CARB fact sheet on health effects: http://www.arb.ca.gov/html/fslist.htm#Health
  3. Conceptual Model: A conceptual model for Air Quality CO does not exist as of June 2011 and is anticipated to be developed in 2011.
  4. Monitoring Plan: A monitoring plan for Air Quality CO does not exist as of June 2011 and is anticipated to be developed in 2012
Last Updated on Monday, 05 November 2012 10:52