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Home Air Criteria Pollutants

PM2.5 24 Hour Average Concentration

Status and Trend

Interpretation and Commentary


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

  • Relevance - This indicator measures the 3-year running average of the 98th percentile 24-hour average concentration of PM2.5. 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 standards have been adopted to protect the public from this pollutant.
  • Adopted Standards - Federal: The 3-year average of the 98th percentile 24-hour PM2.5 concentration must not exceed 35 mg/m3.
  • Indicator - 3-year average of the 98th percentile 24-hour PM2.5 concentration at any monitoring station (mg/m3).
  • Status – The 3-year average of 98th percentile 24-hour PM2.5 concentration for 2007-2009 at Bliss State Park was 15.4 µg/m3 (IMPROVE 2011), which is 44% of the federal standard.  Therefore, a status of “considerably better than target” is designated. Data for the South Lake Tahoe monitoring site has not been collected since 2003, and therefore it is not possible to characterize recent status from that location. According to the data record, the Region has never exceeded the federal 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 the South Lake Tahoe and Bliss State Park sites are not consistent over the monitoring record. For Bliss State Park, there is a long-term trend between 1991 and 2009 of increasing 24 hour PM2.5 concentrations at a rate of +0.27 µg/m3 /year.  This is equal to +0.8% per year of the federal standard of 35 µg/m3. For South Lake Tahoe, there is a long-term trend between 1993 and 2003, of decreasing 24-hour PM2.5 concentrations at a rate of -1.0 µg/m3/year, or -2.9% per year change relative to the standard. The trend determination for this evaluation is based on currently available data from the Bliss site, indicating “little or no change” in PM2.5 based on criteria established for this report.
    • 5 Year Trend - The trend in the last 5 years (2005-2009) at Bliss State Park is not consistent with the long-term trend and indicates an increase in PM2.5 concentration by +2.0 µg/m3 /yr., or +5.7% of the standard per year. Note that short-term trends in air quality are typically not reliable due to the variability of meteorology from one year to the next.

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  • Confidence
    • Status - There is high confidence in the determination for status. These sites used the IMPROVE sampler which is not a Federal Reference Method (FRM) PM2.5 sampler, but is accepted for determining compliance with regional haze regulations. Data from the IMPROVE sample cannot be used to judge attainment of National Ambient Air Quality Standards (NAAQS) for PM2.5. Consistent data from 1993 through 2009 is available for the Bliss State Park site. However, insufficient data has 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 current long-term trend at Bliss State Park for the analysis of 13 data points of the 3-year average 98th percentile 24 hour average concentration is “high,” with a confidence level of 96%, an S = 30, and a P = 0.04. The confidence in the long-term trend determination for the South Lake Tahoe site with 7 data points was “low,” because of data gaps between 2003 and 2010.
    • 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. No 5-year trend could be estimated for the South Lake Tahoe site due to insufficient data. Overall confidence rating for trend is “moderate.”
    •  Overall Confidence - The overall confidence in the status and trend determination is “moderate,” because of the “high” confidence rating for status, and “moderate” confidence rating for trend.
  • Human and Environmental Drivers - Particulate matter pollution consists of very small liquid and solid particles in the air. 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 primary emissions (PM2.5 directly emitted from sources), condensation of semi-volatile organic gases, 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). 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) is available for South Lake Tahoe. The South Lake Tahoe site is expected to represent basin-wide maximum PM2.5 concentrations. 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 3-year average of the 98th percentile 24-hour average concentration of particulate matter less than or equal to 2.5 microns in size (PM2.5) at Bliss State Park from 1993 through 2009, and at the South Lake Tahoe site from 1993 through 2003. These concentrations have been substantially better than the federal standard. The trend determination for this evaluation is based on currently available data from the Bliss site, indicating a “moderate decline” (or increasing concentration) 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 Annual Average 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 10:51