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Rocky Mountain National Park, Colorado, photograph National Park Service

Ozone Exposures: The Status of the National Parks - 2015-2017

Allen S. Lefohn, Ph.D.
A.S.L. & Associates
Helena, Montana 59601
August 9, 2018

Summary

The recent publishing of the EPA design values offers an opportunity to quantitatively evaluate for the period 2015-2017 the status of ozone exposures in the national parks in the United States. Ozone data from 43 monitors in the US national park system were evaluated for potential human health risk. Controlled human laboratory studies have shown that there is a disproportionately greater pulmonary function response from higher hourly average ozone concentrations than from lower hourly average values. For establishing the 2015 ozone standard of 0.070 ppm (70 ppb) for human health, EPA mainly focused on the results associated with clinical studies. While there are some sites in the national park system that experienced frequent occurrences of elevated ozone concentrations, many ozone monitoring sites in the park system experienced no or infrequent occurrences of daily maximum 8-h average concentrations greater than 70 ppb. Using the weighting methodology described in the American Lung Association's State of the Air Report, 61% of the monitoring sites in the park system received a grade of either "A" or "B", 12% received a grade of "C", and 28% received a grade of either "D" or "F". The percent total is greater than 100% due to rounding. Both the (a) Sequoia and Kings Canyon National Parks (NPs) and (b) Joshua Tree National Park (NP) experienced some of the most frequent enhanced ozone exposures in the park system. To better place into perspective the ozone exposures experienced at these two national park sites with the site experiencing the highest design value in the United States, the ozone exposures experienced at the two sites in California were compared with the site located at Crestline in San Bernardino County, California. The Crestline site is in the Los Angeles-South Coast Air Basin, which includes all of Orange County and the non-desert regions of Los Angeles County, Riverside County, and San Bernardino County. Many of the highest ozone exposures in the Los Angeles-South Coast Air Basin occur outside of Los Angeles County. The Crestline site experienced a greater number of days in the high concentration red (86-105 ppb) and purple (106-200 ppb) categories than the two park sites. This reflects a greater risk to human health at Crestline than at (a) Sequoia and Kings Canyon NPs and (b) Joshua Tree NP.

 

Analyses

On July 24, 2018, the US EPA published design values (DV) for ozone and other air pollutants on its website (https://www.epa.gov/air-trends/air-quality-design-values). Design values are used to designate and classify nonattainment areas, as well as to assess progress towards meeting the US National Ambient Air Quality Standards (NAAQS). The recent publishing of the EPA design values offers an opportunity to quantitatively evaluate for the period 2015-2017 the status of ozone exposures in the national parks in the United States. The level of the current 8-hour ozone NAAQS is 0.070 parts per million (ppm), which is commonly referred to as 70 parts per billion (ppb). The ozone design value calculated by the EPA is the 3-year average of the annual 4th highest daily maximum 8-hour ozone concentration.

In addition to publishing design values, the EPA also provides guidance to the States and Tribes on informing the public on ozone concentrations experienced across the US. For informing the public, the daily maximum 8-hour ozone values are summarized in the form of an Air Quality Index (AQI). The index provides information how clean or polluted the air is, and what associated health effects might be a concern to the public. Daily maximum 8-hour ozone concentrations are calculated from the hourly average ozone concentrations recorded. Besides ozone, EPA calculates the AQI for four other major air pollutants (particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide). For each of these pollutants, EPA has established national air quality standards to protect public health. The AQI for ozone corresponds to the following daily maximum 8-hour ozone concentrations:


For assessing the status of ozone 8-hour exposures in the national parks, both the 3-year (2015-2017) design values calculated by the EPA and the weighted mean of the (a) unhealthy for sensitive groups, (b) unhealthy, (c) very unhealthy, and (d) hazardous categories were calculated. For all monitoring sites in the US for the period 2015-2017, no 8-hour ozone concentrations greater than 200 ppb have been reported. Following the analytical methodology used by the American Lung Association's annual State of the Air Report, a weighted mean is calculated using weighting factors applied to each range of daily 8-hour concentrations associated with the Air Quality Index levels described above. The number of orange days (unhealthy for sensitive groups) experienced by each county received a factor of 1; red days (unhealthy), a factor of 1.5; purple days (very unhealthy), a factor of 2; and maroon days (hazardous), a factor of 2.5. The greater weighting to the higher daily maximum 8-hour ozone values follows the scientific results associated with clinical studies for lung function decrement. Controlled human laboratory studies have shown that there is a disproportionately greater pulmonary function response from higher hourly average ozone concentrations than from lower hourly average values. Therefore, the simple addition of the number of daily maximum 8-hour concentrations above 70 ppb does not adequately reflect the potential human health risk associated with ozone exposures because all concentrations are treated equivalently for potential impact. A weighting scheme as outlined above for the daily maximum 8-hour concentrations reflects the clinical study results on which the 2015 ozone standard for human health is based. For more information on this subject, please see Section 2 and the Supplement File of the 24-authored paper by Lefohn et al. (2018), Tropospheric Ozone Assessment Report: Global ozone metrics for climate change, human health, and crop/ecosystem research and the US Federal Register summarizing EPA's decision on the 2015 ozone standard.

The weighted average approach provides greater weight for those days when ozone levels are higher compared to those levels when the values are lower but still above 70 ppb. For calculating the weighted average for the period 2015-2017, the total number of days within each AQI category as noted above is multiplied by their assigned factor and then summed to calculate a total. The total is divided by three to determine the weighted average over the three-year period 2015-2017.

Applying the American Lung Association's methodology, the weighted average defines a letter grade as follows:

Applying the methodology described above, data from the 43 ozone monitors located in the national park system were analyzed. The figure below summarizes the analysis.

 

 

The table below represents the results.

The grading scores for the 43 monitors are summarized as follows:

Percentage total is greater than 100% due to rounding

Sixty-one percent of the monitoring sites in the park system received a grade of either "A" or "B", 12% received a grade of "C", and 28% received a grade of either "D" or "F". The following 12 monitoring sites of the 43 sites in the national park system received either a grade of "D" or "F":

Acadia NP, ME (23-009-0102)
Cape Cod Nat Seashore, MA (25-001-0002)
Chamizal Nat Memorial, TX (48-141-0044)
Death Valley NP, CA (06-027-0101)
Dinosaur NM, UT (49-047-1002)
Indiana Dunes Nat Lakeshore, IN (18-089-0022)
Joshua Tree NP, CA (06-065-0008)
Joshua Tree NP, CA (06-071-9002)
Saguaro NP, AZ (04-019-0021)
Sequoia & Kings Canyon NPs, CA (06-107-0006)
Sequoia & Kings Canyon NPs, CA (06-107-0009)
Yosemite NP, CA (06-043-0003)

For the 2015-2017, the two highest weighted averages of the sites analyzed were experienced in Sequoia and Kings Canyon NPs (06-107-0009 and 06-107-0006). Ozone levels at Sequoia & Kings Canyon NPs are downwind of many air pollution sources, including agriculture, industry, major highways, and urban pollutants from as far away as the San Francisco Bay Area. The third highest weighted average occurred in Joshua Tree NP (06-071-9002). The Los Angeles basin, with a large population, is the major contributor of ozone and other pollutants to Joshua Tree NP. A comparison of the ozone levels at the highest Sequoia and Kings Canyon NPs site and the Joshua Tree NP site was made with the site that experienced the highest ozone design value and weighted average in the United States. The site is located at Crestline in San Bernardino County, California (AQS ID 06-071-0005). The Crestline site is in the Los Angeles-South Coast Air Basin, which includes all of Orange County and the non-desert regions of Los Angeles County, Riverside County, and San Bernardino County. Many of the highest ozone exposures in the Los Angeles-South Coast Air Basin occur outside of Los Angeles County. The monitor is in a residential area in San Bernardino County. There is a considerable difference between the two park sites and the Crestline site when comparing design values and weighted averages. The design values and the weighted averages calculated for each of the three sites are as follows:

For 2015-2017, while both (a) Sequoia and Kings Canyon NPs and (b) Joshua Tree NP experienced 35 and 12 days, respectively, in the red category (i.e., 86-105 ppb range) and no occurrences in the purple category (106-200 ppb range), the Crestline site in San Bernardino, CA experienced 115 days in the red category and 25 days in the purple (106-200 ppb) category. The Crestline site experienced a greater number of days in the higher concentration red and purple categories. While the two national park sites experienced some of the highest ozone exposures in the national parks, the exposures at Crestline reflect a greater risk to human health.

Conclusion

While there are some sites in the park system that experience frequent occurrences of elevated ozone concentrations, many ozone monitoring sites in the park system experience zero or infrequent occurrences of daily maximum 8-h average concentrations greater than 70 ppb. Sixty-one percent of the monitoring sites in the park system received a grade of either "A" or "B", 12% received a grade of "C", and 28% received a grade of either "D" or "F". The percent total is greater than 100% due to rounding. Both the (a) Sequoia and Kings Canyon NPs and (b) Joshua Tree NP experienced some of the most frequent enhanced ozone exposures in the park system. To better place into perspective the ozone exposures experienced at these two national park sites with the site experiencing the highest design value in the United States, the ozone exposures experienced at the two sites were compared with the site located at Crestline in San Bernardino County, California. The Crestline site is in the Los Angeles-South Coast Air Basin, which is composed of several counties in the Los Angeles area. The Crestline site experienced a greater number of days in the red (86-105 ppb) and purple (106-200 ppb) categories when compared to the two park sites. This reflects a greater risk to human health at Crestline than at (a) Sequoia and Kings Canyon NPs and (b) Joshua Tree NP.

 

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