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Home Air Greenhouse Gases

Carbon Monoxide 8 Hour Average Concentration

Status and Trend

Interpretation and Commentary

Considerably Better Than Target
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Status: Considerably Better Than Target
Trend: Rapid Improvement
Confidence: High

  • Relevance - Carbon monoxide (CO) in high concentrations affects human health by reducing the supply of oxygen to the tissues of the body. Health effects can include headaches, nausea, reduced mental alertness and even death, at very high concentrations. TRPA, federal and state standards, with varying time averaging periods, have been adopted to protect the public from this harmful pollutant. This indicator addresses the highest and second highest monitored CO concentrations averaged over every 8 hours for the calendar year.
  • Adopted Standards - TRPA: Highest 8-hour average of 9 ppm – not to be exceeded, California and Nevada: Highest 8-hour average of 6 ppm is not to be exceeded, Federal: Highest 8-hour average of 9 ppm – not to be exceeded more than once per year.
  • Indicators - First and second highest 8-hour CO concentration (ppm). Only the highest 8-hour concentration is used to determine compliance with adopted standards. The 2nd highest is provided to demonstrate the magnitude of difference between the highest and 2nd highest recorded 1-hour concentration in the Region.
  • Condition Status – The Region has been in compliance with the strictest standard since 2003. The 2010 1st highest and 2nd highest 8-hour average carbon monoxide (CO) concentration values were 1.9 ppm and 1.6 ppm respectively (EPA 2011a). The highest 8-hour average concentration is equal to 32% of the most stringent (CA and NV) standard of 6 ppm (68% below standard). The 2nd high value is equal to 27% of the most stringent standard of 6 ppm (73% below standard). Consequently, the status was determined to be “considerably better than target.”
  • Trend – Trends were calculated using the Thiel regression method which is academically well accepted for air quality analysis.
    • Long Term Trends - The long-term trend indicates a decreasing highest 8-hour average CO concentration at the Horizon site between 1983 and 1998, and at the Harvey’s site between 2000 and 2010. The trend represents a change in concentration of -0.4 ppm/year at both the Horizon and Harvey’s sites. These rates are -6.7% per year of the most stringent (CA and NV) standard of 6 ppm, so the long-term trend designation is “rapid improvement”.
    • 5 Year Trend - The trend over the most recent 5 years (2006-2010) is consistent with the long-term trend, and indicates decreasing first high 8-hour average CO concentrations. The regression analysis of the last 5 years of data indicated a -0.3.ppm/year reduction in CO concentration.

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  • Confidence
    • Condition Status - There is high confidence in the condition status because the data is collected using federal reference methods2, is subject to extensive quality assurance requirements and were collected continuously between 1983 and 2010 (except 1999).
    • Long Term Trends - The confidence in the trend for the first high 8-hour average values at the Horizon site is high for the long range analysis of 16 data points, with a confidence level of 100%, a S-value of -97, and a P value of <0.01. The confidence in the trend for the 1st highest values at the Harvey’s site is also high for 11 data points, with a confidence level of 98%, a S-value of -28, and a P value of 0.02.
    •  5 Year Trend - The confidence in the trend for first high over the most recent 5 years (2006-2010) is moderate with a confidence level of 76%, a S value of -4 and a P value of 0.24..
    •  Overall Confidence - The overall confidence in the status and trend determination is high because there is high confidence in the status and long-term trend. Although confidence in the short-term trend is only moderate, data for the last five years indicates 8-hour CO concentrations is well below the strictest standard.
  • Human and Environmental Drivers - Carbon monoxide is emitted from incomplete fuel combustion by sources such as cars, trucks, boats, construction equipment, fireplaces, woodstoves, furnaces and wildfire. The ambient concentration of CO is highly dependent on meteorological conditions such as temperature, wind speed, and mixing conditions.
  • Monitoring Approach – Between 1983 and 1998, carbon monoxide was monitored at the Horizon Hotel in Stateline, NV. In 1998, the monitoring site was relocated to Harvey’s Resort parking garage in Stateline, NV. The site is designed to monitor the highest CO concentrations at Lake Tahoe, and is intended to be representative of both the CA and NV sides of the south shore resort district. Data is collected, analyzed and reported by the Nevada Division of Environmental Protection (NDEP).3
  • Monitoring Partners– Nevada Division of Environmental Protection, U.S. Environmental Protection Agency, and Tahoe Regional Planning Agency

Links

 
  • Monitoring Plan
  • Conceptual Model

Map

Carbon Monoxide Monitoring Locations in the Lake Tahoe Basin

Carbon Monoxide monitoring locations

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Trend Charts

The highest and second highest 8-hour-average carbon monoxide (CO) concentration from the year 1983 through 2010 at the Stateline monitoring sites. All concentrations are better than federal and TRPA standards and most are better than the more stringent state standards. The long term trends show rapid improvement from1983-1998 and 2000-2010. The discontinuity in data during 1999 is caused by movement of the monitoring site.
Source: U.S. Environmental Protection Agency, Air Data
Nevada Division of Environmental Protection

Additional Info

References

  1. U.S. Environmental Protection Agency, AirData website, April 26, 2011: http://www.epa.gov/aqspubl1/.
  2. EPA methods for air quality monitoring: http://www.epa.gov/ttn/amtic/files/ambient/criteria/reference-equivalent-methods-list.pdf
  3. Nevada Air Quality Trend Report, 1998-2009. Nevada Division of Environmental Protection, Bureau of Air Quality Planning, January 2011. http://ndep.nv.gov/baqp/monitoring/docs/trend.pdf

Additional Information

  1. Carbon Monoxide 1 hr avg. 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 10:33