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Home Air Criteria Pollutants

Ozone: Oxides of Nitrogen Emissions (Average tons/day)

Status and Trend

Interpretation and Commentary

Oxides of Nitrogen Emissions

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Status: At or somewhat better than target
Trend: Moderate Improvement
Confidence: Low

  • Relevance - This indicator estimatesthe daily emissions of NOx based on the California Air Resources Board (CARB) Emission Inventory for the California portion of the Lake Tahoe Region. Nitrogen dioxide is one of a group of highly reactive gasses known as “oxides of nitrogen,” or “nitrogen oxides.” Other nitrogen oxides include nitrous acid and nitric acid. While federal standards cover the entire group of NOx, NO2 is the component of greatest interest, and the indicator for the larger group of NOx. In addition to contributing to the formation of ground-level ozone and fine particle pollution, NO2 is linked with regional haze, global warming, water quality degradation, and a number of adverse effects on the respiratory system (EPA 2011e). Current scientific evidence links short-term NO2 exposure (30 minutes to 24 hours) with adverse respiratory effects, including airway inflammation in healthy people, and increased respiratory symptoms in people with asthma (EPA 2011c).
  • Adopted Standards - TRPA: Maintain oxides of nitrogen (NOx) emissions at or below the 1981 level (i.e., maintain oxides of nitrogen (NOx) emissions at or below 9.4 tons per day for an average summer day, as reported in the Study Report for the Establishment of Environmental Threshold Carrying Capacities (TRPA 1982a)); CA: Annual average NO2 concentration not to exceed 30ppb (0.030 ppm), highest one-hour, not to exceed 0.18ppm; NV/Federal:Annual averageNO2 concentration not to exceed 53ppb (0.053ppm), highest one-hour not to exceed 0.10 ppm.
  • Indicators - Average tons/day of NOx emission (ton/day), annual and highest one-hour NO2 concentrations (ppm).
  • Condition Status – Based on the CARB Emission Inventory for the California portion of Lake Tahoe Region, NOx emissions in 2010 were estimated at 4.95 tons per day, which is about 11% lower than the 1980 (the date closest to the date identified in the adopted Threshold Standard) estimate of 5.56 tons per day, and 29% lower than the 1990 estimate of 7 tons/day. Based on emission estimates for the California portion of the Basin in 2010, it was concluded that the current status determination is “at or somewhat better than target,” because emission estimates were below 1980 estimates for the California portion of the Basin. TRPA (1982a) estimated NOx emissions in 1980 for the entire Lake Tahoe air basin at 9.4 tons/day. Preliminary results from the new TRPA monitoring station (August through November 2011) indicated that the highest average 1-hour NO2 concentration was 0.02 ppm. These results preliminarily indicate that the Region is meeting the California and federal 1-hour NO2 standard of 0.18ppm and 0.10ppm, respectively.
  • Trend – Based on the California Air Resources Board (CARB) emissions inventory estimates for the California portion of the Lake Tahoe Region, average per day NOx emissions have decreased at a rate of -0.035 tons/day since 1980 and are projected to continue to decrease through 2020. This represents a -0.6% percent change resulting in a trend determination of “moderate improvement.”

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  • Confidence - Because NOx emissions are based on modeled outputs and the estimates only represent the California portion of the Lake Tahoe air basin, a “low” confidence rating is assigned to both status and trend determinations.
  • Human and Environmental Drivers - NOx gasses are formed during fuel combustion. NOx forms quickly from emissions from cars, trucks and buses, power plants, and off-road equipment.NOx reacts with ammonia, moisture, and other compounds to form nitric acid vapor and related particles (EPA 2011c). Small particles can penetrate deeply into lung tissue, causing premature death in extreme cases. Inhalation of such particles may cause or worsen respiratory diseases such as emphysema and bronchitis, and it may also aggravate existing heart disease. NOx reacts with volatile organic compounds in the presence sunlight to form Ozone. Ozone can cause adverse effects such as damage to lung tissue and reduction in lung function, mostly in susceptible populations (children, elderly, and asthmatics). Ozone can be transported by wind currents and cause health impacts far from the original sources.
  • Monitoring Approach – California Air Resources Board (CARB) compiles data to create the criteria pollutant emission inventory, which includes information on the emissions of reactive organic gases (ROG), oxides of nitrogen (NOx), oxides of sulfur (SOx), carbon monoxide (CO), and particulate matter (PM10). Data are gathered on an ongoing basis and stored in the California Emission Inventory Development and Reporting System (CEIDARS). A summary of the criteria pollutant inventory is published annually. The California emission inventory contains information on the following air pollution sources:
    • Stationary sources - approximately 13,000 individual facilities, called point sources. Point sources are fixed pollution sources such as electric power plants and refineries. There are also about 135 aggregated point source categories. These categories estimate emissions for the non-point source stationary sources.
    • Area-wide sources- approximately 80 source categories. An area-wide source category is made up of sources of pollution mainly linked to the activity of people. Examples of these sources include consumer products and architectural coatings used in a region.
    • Mobile sources- all on-road vehicles such as automobiles and trucks; off-road vehicles such as trains, ships, aircraft; and farm equipment.

The principal agencies contributing data to the stationary and area-wide source inventory are the CARB and the California air pollution control and air quality management districts. The CARB, the California Department of Transportation (Caltrans), and regional transportation agencies are the principal agencies involved in developing the mobile source inventory. Information represented in the California emission inventory is a snap-shot of a variety of dynamic and variable processes. As such, the emission inventory can only represent an estimate of what is actually occurring. In summer 2011, a new NOx monitoring station was established at the TRPA Stateline, NV office. This site will be used for future NOx concentration monitoring and reporting.

  • Monitoring Partners– California Air Resources Board and Tahoe Regional Planning Agency. Funding for the TRPA NOx monitoring site was provided by Nevada Department of Motor Vehicles.


  • Monitoring Plan
  • Conceptual Model


NOx Monitoring Locations in the Lake Tahoe Basin

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Trend Charts

Chart data not available at this time.
Trend in estimated Nitrogen Oxide emissions (tons/day) for the California portion of the Lake Tahoe Region. Source: CARB (2008) Emission Inventory for the California Portion of the Lake Tahoe Air Basin.

Additional Info


  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. Washoe County Air Quality Management Division website, April 26, 2011:http://www.co.washoe.nv.us/health/aqm/home.html
  4. California Air Resources Board website, April 26, 2011:http://www.arb.ca.gov/adam/.

Additional Information

  1. Ozone 8 hr avg. Indicator
  2. Ozone 3 yr 4th high 8 hr avg. Indicator
  3. CARB fact sheet on health effects: http://www.arb.ca.gov/html/fslist.htm#Health
  4. Conceptual Model: A conceptual model for Air Quality CO does not exist as of June 2011 and is anticipated to be developed in 2011.
  5. 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 10:40