Highest 1-Hour Concentration of Carbon Monoxide
This threshold indicator has been retired and is no longer reported.
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. Federal and state standards with varying time-averaging periods have been adopted to protect the public from this pollutant. This indicator addresses the highest carbon monoxide concentrations averaged over every one hour for the calendar year.
Carbon monoxide is created by incomplete fuel combustion and emitted by sources such cars, trucks, boats, construction equipment, fireplaces, woodstoves, furnaces, and wildfire.
Evaluation Map
Carbon monoxide monitoring sites located at Horizon and Harvey’s Casinos in the Lake Tahoe Basin.
2015 Evaluation
- Status
- Considerably Better Than Target
- Trend
- Moderate Improvement
- Confidence
- Moderate
Applicable Standard
TRPA does not have an adopted standard for this indicator so the strictest California state standard is used instead.
Key Points
- The Tahoe Region has been well within compliance with the TRPA, State, and Federal standards for many years.
About the Threshold
- 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. Federal and state standards with varying time-averaging periods have been adopted to protect the public from this pollutant. This indicator addresses the highest CO concentrations averaged over every 1 hour for the calendar year.
- Carbon monoxide is created by incomplete fuel combustion and emitted by sources such cars, trucks, boats, construction equipment, fireplaces, woodstoves, furnaces, and wildfire.
Delivering and Measuring Success
Rationale Details
- The Region has been well within compliance with the TRPA, State and Federal standards for many years. In April of 2012, The NDEP submitted its' second 10-year Maintenance Plan to EPA recommending that the monitoring site be discontinued due to the low concentrations recorded at the sites. In explaining the decision to discontinue monitoring, NDEP writes, "NDEP concludes that 33 years of clean data, all of it under 80 percent of the NAAQS and most recently at 34 percent, with on-going downward trends is sufficient evidence of continued attainment through 2024...(NDEP 2012)." Prior to discontinuation of the monitoring site, a high recording of 29.1 ppm was recorded, but is believed to a be a false/faulty reading. The 2012 reading was nearly double the "exceptional events" readings recorded during wildfire 2003/2004 and was almost three times the level that would be expected based on the long term trend in the data. The 2012 reading did not exceed the 1hr NV state standard (35 ppm) and was thus not flagged for additional analysis by NDEP.
Surrogate monitoring conducted by TRPA recorded a maximum 1-hour CO reading of 4 ppm during the current monitoring period. While the TRPA monitor is not "official" data because the monitoring station has not been approved by the EPA, it provides quality assured data and is further evidence to support the belief that the 29.1ppm levels recorded in 2012 were not accurate. For these reasons, the 2012 reading is not used to assess status and instead the long term trend line is used. The long term trend line shows the current status as considerably better than target. - The long-term trend lines indicate statistically significant decreasing trends at the Horizon site between 1983 and 1998, and at the Harvey's site between 2000 and 2012 (Campbell 2015). 1-hour CO concentrations decreased by an average of 0.3 ppm per year at the Harvey's site, which is a decrease of 1.5 percent per year in relation to the standard of 20 ppm. Therefore, a trend of moderate improvement was determined. The 2012 data appears to be an anomaly and was not indicative of the overall trend.
Confidence Details
- Moderate. There is moderate confidence in the status because data was collected using widely accepted protocols, are subject to quality assurance requirements, and were collected consistently between 1983 and 2012 with the exception of moving the monitoring site approximately one-quarter mile in 1999. While only one monitoring site is used to determine indicator status, the monitoring site is located within the South Shore Resort District that represents the greatest volume of vehicle traffic in the Region, and the measurements are thought to represent the highest source of CO emissions. Confidence would be "high," but moving the monitoring location one-quarter mile in 1999 significantly changed CO levels, raising questions about the representative nature of data (Campbell, D. 2016)
- Moderate. Confidence in the trend at the Stateline Harvey's site is moderate (p = 0.18).
- Moderate.
Additional Figures and Resources
No photos available.
No documents available.