3-Year Average of the 4th Highest 8-hour Average Concentration of Ozone
This threshold indicator has been retired and is no longer reported.
This indicator addresses the 3-year average of the 4th-highest 8-hour average ozone concentration, which is the basis of the federal standard. Ozone (O3), in high concentrations can cause health effects such as lung inflammation and other respiratory illness. Ozone can also cause damage to trees and plants at concentrations lower than the human health based ambient air quality standards. TRPA, and federal and state standards, with varying time averaging periods, have been adopted to protect the public from this harmful pollutant.
Ozone is considered a secondary pollutant, created by photochemical reactions between hydrocarbons (HC) and oxides of nitrogen (NOx) in sunlight. The sources of HC and NOx include mobile sources (cars, trucks, boats, aircraft, off-road vehicles, etc.), biomass burning (wood stoves, wildfires, prescribed burning), and consumer products such as solvents. Ozone is transported from populated areas around the Lake Tahoe Region into the basin, and the ambient concentration of O3 is highly dependent on meteorological conditions such as sunlight, temperature, wind speed and mixing conditions.
Status
Desert Research Institute
Evaluation Map
Ozone monitoring locations in the Lake Tahoe Basin.
2015 Evaluation
- Status
- At or Somewhat Better Than Target
- Trend
- Moderate Improvement
- Confidence
- High
Applicable Standard
Federal: The 3-year average of the 4th-highest daily maximum must not exceed concentration standard of 0.075 ppm.
Key Points
- The indicator has been in attainment at all monitoring locations since 1993.
About the Threshold
- This indicator addresses the 3-year average of the 4th-highest 8-hour average ozone concentration, which is the basis of the federal standard. Ozone (O3), in high concentrations can cause health effects such as lung inflammation and other respiratory illness. Ozone can also cause damage to trees and plants at concentrations lower than the human health based ambient air quality standards. TRPA, and federal and state standards, with varying time averaging periods, have been adopted to protect the public from this harmful pollutant.
- Ozone is considered a secondary pollutant, created by photochemical reactions between hydrocarbons (HC) and oxides of nitrogen (NOx) in sunlight. The sources of HC and NOx include mobile sources (cars, trucks, boats, aircraft, off-road vehicles, etc.), biomass burning (wood stoves, wildfires, prescribed burning), and consumer products such as solvents. Ozone is transported from populated areas around the Lake Tahoe Region into the basin, and the ambient concentration of O3 is highly dependent on meteorological conditions such as sunlight, temperature, wind speed and mixing conditions.
Delivering and Measuring Success
Rationale Details
- Of all the monitoring stations where recent data is available, the
highest 3-year average of the 4th-highest daily maximum ozone concentration was 0.064 ppm in Incline Village, 85 percent of the standard (Campbell 2015). Therefore, a status of “somewhat better than target” was determined. The indicator has been in attainment at all monitoring locations since 1993. - The trend line for all monitoring stations since 1986 shows a decrease of 0.0004 ppm per year, a decrease of 0.53 percent per year in relation to the standard of 0.075 ppm (Campbell 2015). Therefore, a trend of moderate improvement is determined.
Confidence Details
- High. There is high confidence in the status determination because data is collected using federal reference methods (EPA 2011a), are subject to quality assurance requirements, and are collected continuously across the Region since 1975.
- High. Confidence in the trend is high with a confidence in a trend of 99 percent (P = 0.01)
Additional Figures and Resources
No photos available.
No documents available.