Ozone (O3), one of the EPA criteria pollutants, is a pale blue gas with a distinctive pungent smell. The oxygen we breathe that is necessary for life is made of two oxygen molecules, while ozone is made up of three oxygen molecules. Ozone is found at the highest concentrations in two regions of the atmosphere (EPA, 2013g):
- In the upper atmosphere, roughly 12 - 19 miles above ground (i.e., the ozone layer)
- Naturally occurring
- Beneficial: blocks certain types of ultraviolet radiation
- At ground level
- Largely from human sources
- Major component of air pollution
- Can be harmful to your health
Health Effects | Top
Even at relatively low levels, exposure to ozone can cause harmful health effects, particularly of the lungs and respiratory system.
Populations sensitive to ozone air pollution (UDAQ, 2014c)
- People with preexisting lung conditions, including:
- Children, whose lungs are still developing and who are more likely to have asthma and play outdoors
- Older adults, who may have otherwise undiagnosed lung conditions
- People who work or exercise vigorously outdoors
- Otherwise healthy people who are unusually sensitive to ozone
The initial symptoms of ozone exposure may go away over time, particularly when the exposure lasts for several days. However, ozone can continue to damage the lungs even when symptoms are no longer noticeable.
- Aggravation of respiratory diseases
- Irritation of the respiratory system:
- Pain when taking a deep breath
- Throat soreness or irritation
- A feeling of tightness in the chest
- Reduced lung function
- Difficulty in breathing deeply and vigorously
- Shortness of breath
- Inflammation of the airways, possibly causing damage
- Can make the lungs more susceptible to infection
- Over time, permanent damage can result
These health effects can lead to increased school and work absences, visits to doctors and emergency rooms, and hospital admissions. Research has suggested that ozone exposure may increase the risk of death due to lung or heart disease. The frequency and severity of the health effects tends to increase as the concentrations of ozone increase. A recent study found that maternal exposure to ozone during the second and third trimesters was associated with reduced birth weight (Salam et al., 2005).
Ways to Reduce Exposure | Top
People are typically exposed to ozone when they are outdoors when ozone levels are high, and the amount of exposure is determined by the ozone concentration and the amount of air a person breathes over time. Any activity that increases the rate and depth of breathing, such as physical exertion, will increase that person’s exposure to ozone, and consequently the likelihood and severity of health effects (EPA, 2013g; UDAQ, 2014c).
Protect your health when ozone levels are high:
- Monitor ozone levels in your area
- Reduce the amount of time you are active outdoors
- Since exercise is good for your health, it is important to both stay active as well as know when to make changes
- Schedule your outdoor activities for the morning or evening when ozone levels are typically lower
- Substitute lower intensity activities (e.g., take a walk instead of jogging or running)
Sources | Top
Ground level ozone (usually just referred to as ozone) is not released directly into the air, but is instead created by chemical reactions between nitrogen oxides (e.g., nitrogen dioxide) and volatile organic compounds (VOCs). In the presence of sunlight, nitrogen oxides and VOCs break apart and recombine into new compounds, including ozone (UDAQ, 2014c). Motor vehicle exhaust; emissions from industrial facilities, refineries, and power plants; gasoline vapors; and chemical solvents are some of the major sources of nitrogen oxides and VOCs, and thus ozone (EPA, 2013g).
Ozone can reach unhealthy levels on hot, sunny days in regions with high concentrations of the nitrogen oxides and VOC precursors, such as urban areas. Ozone and its precursors can also be transported long distances by wind, so even rural areas can experience high ozone levels (EPA, 2013g). Ozone contributes to the smog or haze typically associated with air pollution. Due to the long range transport potential for ozone precursors, wildfires and urban emissions from other continents can also contribute to local ozone formation (UDAQ, 2014c).
Ozone in the Uintah Basin | Top
While ground level ozone is typically associated with summer, elevated levels have also been observed in winter at a few high elevation areas in the Western U.S. with high concentrations of local emissions of nitrogen oxides and VOCs. One such region is the Uintah Basin in northeastern Utah, a largely rural area with a sparse population. High ozone levels in the Uintah Basin during the winter are thought to only occur when the ground is snow covered, a temperature inversion traps emissions close to the ground, and the skies are sunny (Figure 1) (UDAQ, 2014d).
Figure 1: Average daily max 8-hour ozone concentration in the Uintah Basin, 2010 – 2016
The winter of 2011 – 2012 was relatively mild with little snow cover, and ozone levels remained below the National Ambient Air Quality Standard (NAAQS). By contrast, the winter of 2012 – 2013 saw plenty of snow, and ozone levels exceeded the NAAQS a number of times (UDAQ, 2014e). Recent studies have determined that oil and gas operations in the Basin are responsible for 98 – 99% of VOC emissions and 57 – 62% of nitrogen oxide emissions. Natural gas production generated the highest percentage of VOC emissions, while population centers had the highest levels of nitrogen oxides (UDAQ, 2014d). The Utah Department of Environmental Quality continues to study winter ozone in the Uintah Basin.
Standards and Trends | Top
The primary and secondary National Ambient Air Quality Standards (NAAQS) for ozone are 0.070 parts per million (ppm) based on an eight hour average. This has been revised several times, most recently in 2015 when it was lowered from the previous standard of 0.075 ppm (EPA, 2013h). Since weather conditions play such a large role in the data collected year to year, this standard is evaluated over rolling three year periods.
Nationally, average ozone levels have shown a slow but steady decline since 1980, with a 32% overall decrease (Figure 2).
Figure 2: Average national ozone concentration, 1980 - 2015
Ozone levels in the Southwest region states of Arizona, Colorado, New Mexico, and Utah have remained relatively stable throughout the last decade, with a slight decreasing trend (Figure 3).
Figure 3: Average ozone concentration in the Southwest, 2000 – 2015
Along the Wasatch Front, ozone concentrations have also been fairly stable, rising over the 1990s before declining to return to levels below the NAAQS by the 2010s (Figure 4).
Figure 4: 3-year average of the annual 4th highest daily maximum 8-hour average ozone concentration along the Wasatch Front, 1990 – 2015
The typical seasonal variation in ozone pollution, high in the summer and low in the winter, can be clearly seen in Figure 5.
Figure 5: Average daily max 8-hour ozone concentration along the Wasatch Front, 1990 – 2014
Two areas in Utah, Davis and Salt Lake Counties, have been designated as maintenance areas by EPA (Figure 6).
Figure 6: Ozone maintenance areas in Utah
Data and Indicators | Top
The Utah Environmental Public Health Tracking Program (EPHT) has created a number of indicators exploring data on ground level ozone in Utah. An indicator is a fact or trend that indicates the level or condition of something. Well known indicators include gross national product, unemployment rates, and presidential approval ratings. In a public health context, indicators show trends like cancer rates, drinking water contamination levels, and blood lead levels in children. Visit the EPHT frequently asked questions page for more information.