This article is a part of the NASA DEVELOP’s Spring 2017 Article Session. For more articles like these, click here
In large quantities, tropospheric ozone can negatively impact humans and vegetation, but ground-level stations only sample a portion of the atmosphere. This project assessed how NASA satellite data in conjunction with ground stations can enhance education efforts of the National Park Service.
Authors:
Tyler Rhodes
Amy Wolfe
Emily Beyer
Eric White
Amber Showers
Emily Gotschalk
The United States National Park Service (NPS) is tasked with preserving the natural and cultural resources and values of all units within the National Park System. Not only does the NPS preserve these unique landscapes for posterity, but it also educates and inspires individuals to care for their environment. However, these park units can be difficult to preserve as natural and anthropogenic impacts are widespread and sometimes challenging to target. One particular challenge for the NPS is preserving scenic landscapes. The NPS has been tasked via the Clean Air Act “to preserve, protect, and enhance the air quality in national parks, national wilderness areas, national monuments, national seashores, and other areas of special national or regional natural, recreational, scenic or historic value” (1). Not only is this a federal mandate, but it is important for park visitation, as park guests are often drawn to park units to see these unique vistas and unaltered landscapes. As such, NASA DEVELOP in conjunction with the NPS, assessed the use of satellite imagery to detect and analyze trends in atmospheric pollutants that affect park views.
One such pollutant is ozone (O3), which is a colorless, odorless reactive molecule comprised of three oxygen atoms. Ozone occurs throughout the upper and lower atmosphere, but the location and origin determines whether the effects of the ozone are beneficial or harmful (8). The troposphere, the lowest layer of the atmosphere, stretches from the surface of the Earth to approximately 10-15 km in altitude. The next layer, the stratosphere, is located approximately 10-50 km above Earth’s surface and contains the “ozone layer.” The ozone layer extends from about 15-30 km in altitude (2) and acts as a thin sheet protecting the Earth’s surface from harmful ultraviolet radiation emitted by the sun (8). Ozone occurs naturally in the stratosphere and is beneficial for humans and the environment because it blocks ultraviolet radiation known to cause skin cancer and harm marine and plant life (2). Significant depletion of stratospheric ozone has been observed near the South Pole driven primarily through the increase of anthropogenic chemicals such as chlorofluorocarbons (CFCs), which were commonly used in refrigerators and vehicle air conditioners, and have a long life expectancy within the troposphere (10). Commonly known as the “Ozone Hole,” this gap develops through chemical reactions between CFC photolysis products (halogen radicals) and ozone (2).
Figure A. Map of the study area along with the location of the two ground monitoring stations. Image Credit: NASA DEVELOP
Ground-level or tropospheric ozone is a “criteria air pollutant” that poses significant health risks to plants and humans (3). It is formed through a chemical reaction of nitrogen oxides and volatile organic compounds (VOCs) in the presence of sunlight (7). Ground level ozone has been increasing as a result of more fossil fuel combustion. According to the California Air Resources Board, exposure to high ozone levels irritates the respiratory system, can worsen asthma symptoms, and may cause permanent lung damage. The U.S. Department of Agriculture (USDA) states that tropospheric ozone causes more damage to plant life than all other atmospheric pollutants combined (4). Tropospheric ozone damages forests in many ways, including foliar damage, which decreases photosynthesis and increases leaf senescence. These effects increase the vegetation’s susceptibility to drought, invasive species infestation, and wildfire. Understanding tropospheric ozone is important for the NPS, as it has the responsibility to protect natural resources affected by air pollution and deliver high ozone advisories to the public.
Ground-level ozone is difficult to measure over broad geographic areas and various methods have been established to accomplish accurate measurements using satellite sensors. A common method is to use one of NASA’s Earth observations, Aura, and subtract the stratospheric ozone gathered from its sensor, the Microwave Limb Sounder (MLS), from the total column ozone measured by a different sensor, the Ozone Monitoring Instrument (OMI) (6). Ground monitoring of ozone provides an accurate measurement near the surface for that specific region; however, the stations extrapolate the value over large distances. The confidence in the extrapolation decreases as the distance from the monitoring station increases. Incorporating satellite instruments with the monitoring stations’ measurements could provide supplementary information of the distribution and changes of ozone over large areas with little to no surface measurements (5).
The area of interest in this study was the Appalachian Trail (Figure A), which spans 2,189 miles and traverses 14 states along the east side of the United States.
Started in 1921 by private citizens, the Appalachian Trail was completed in 1937 and is managed today by many federal agencies such as the National Park Service and the US Forest Service, along with state agencies and local volunteers (9). This project studied the entirety of the Appalachian Trail from 2012 to 2015 during the months of May to September. Specifically, the study focused on the hourly measurements made by the Shenandoah ground monitoring station, Big Meadows (Figure B), the Great Smoky Mountain monitoring station, Cove Mountain, measurements from OMI, and MLS to compare and validate the effectiveness of using these sensors to measure air pollutants in the troposphere.
Figure B. Ground station at Big Meadows with Jalyn Cummings. Image Credit: Tyler Rhodes
Tropospheric Ozone Residual (TOR) was calculated for the months of May to September for four consecutive years from 2012 to 2015 to observe the change in ozone during peak months and differences between years (Figure C). TOR is calculated by subtracting the stratospheric ozone amount from the total column ozone amount, leaving only the ozone found in the troposphere. Visually, the months of June and July regularly have high ozone over the entire study area with June 2015 displaying very high ozone. Also observed was a tapering off of ozone from August to September.
After comparing station ozone measurements to calculated TOR from the Aura satellite for 2012, our results revealed the monitoring stations’ measurements were consistently higher compared to the estimated TOR. However, overall, both the ground monitoring stations and TOR calculations showed similar trends with slight differences. The largest differences occurred during the months of May and September, but the differences were still within an acceptable range for the National Park Service to compare to its monitoring station data. The largest difference between the ground monitoring stations and TOR was approximately 15 parts per billion (ppb) while the smallest separation was 1 ppb.
Figure C. Monthly tropospheric ozone residual (TOR) for 2015. Image Credit: NASA DEVELOP
For future studies, the TOR calculation could incorporate more variables such as the changing tropopause height, which is known to naturally fluctuate from the equator to the poles. Also, more advanced satellites could be used to monitor air pollutants such as Tropospheric Emissions: Monitoring of Pollution (TEMPO). TEMPO is planned to be completed mid-2017, and launched in 2019 or later. This instrument will be in a geostationary Earth orbit (GEO) about 22,000 miles above Earth’s equator. The TEMPO instrument is sensitive to ultraviolet and visible wavelengths of light and will maintain a constant view of North America. This will allow the instrument’s light-collecting mirror to face Earth and make hourly scans during the day from the East Coast to the West Coast. The pixels will be 9 square kilometers, unlike the current sensors which are several hundred square kilometers. This will allow for tracking at a much smaller scale, and could help the NPS track pollutant movements across each individual park.
Beyond ozone, other atmospheric concerns like nitrogen and sulfur dioxides and trends in visibility also are important to the NPS. Future DEVELOP projects may explore these issues, as acid rain (from SO2 emissions) damages foliage and aquatic life in many of the parks along the Appalachian Trail. Further, visibility and its relationship with different aerosols in the atmosphere would be beneficial information for the NPS as visibility is one of the key focuses of the Clean Air Act and is a major aesthetic component for visitors to the parks.
References
[1] 42 U.S.C. §7470(2)
[2] Basic Ozone Layer Science. (2016, January 14). [Online]. Available: https://www.epa.gov/ozone-layer-protection/basic-ozone-layer-science
[3] Criteria Air Pollutants. (2016, June 16). [Online]. Available: https://www.epa.gov/criteria-air-pollutants
[4] Effects of Ozone Air Pollution on Plants. (2005, August 25). [Online]. Available: https://www.ars.usda.gov/Research/docs.htm?docid=8453
[5] J. D. Ray, “Ozone Monitoring Protocol for the National Park Service”. National Park Service U.S. Department of the Interior, pp. 1-24, 2004.
[6] J. Fishman, J. K. Creilson, P. A. Parker, E. A. Ainsworth, G. G. Vining, J. Szarka, F. Booker, X. Xu, “An investigation of widespread ozone damage to the soybean crop in the upper Midwest determined from ground-based and satellite measurements”. Atmospheric Environment, 44, pp. 2248-2256, 2010.
[7] N. A. Krotkov, C. A. McLinden, C. Li, L. N. Lamsal, E. A. Celarier, S. V. Marchenko, …D. G. Streets, “Aura OMI observations of regional SO2 and NO2 pollution changes from 2005 to 2015”. Atmospheric Chemistry and Physics, 16, pp. 4605-4629, 2016.
[8] Ozone Basics. (2016, May 16). [Online]. Available: https://www.epa.gov/ozone-pollution/ozone-basics#what_where_how
[9] United States. National Park Service. (n.d.). Appalachian National Scenic Trail (U.S. National Park Service). [Online]. Available: https://www.nps.gov/appa/index.htm
[10] What is the Ozone Hole?. (2013, September 25). [Online]. Available: http://ozonewatch.gsfc.nasa.gov/facts/hole_SH
Author Biographies
Tyler Rhodes is a recent graduate from Old Dominion University. Since working with DEVELOP at NASA Langley Research Center as an independent research consultant, he has moved to Piscah National Forest with the U.S. Forest Service.
Amy Wolfe is a recent graduate from the University of Virginia. Since working with DEVELOP at NASA Langley Research Center as an independent research consultant, she has moved to work with GIS in the private sector.
Emily Beyer is a student at Florida State University, and worked with DEVELOP at NASA Langley Research Center as an independent research consultant on the Appalachian Trail Health & Air Quality project.
Eric White is a student from University of Virginia’s College at Wise, and is working with DEVELOP at Wise County and City of Norton Clerk of Court’s Office.
Amber Showers is a recent graduate from University of Virginia’s College at Wise, and worked with DEVELOP at the Wise County and City of Norton Clerk of Court’s Office on the Appalachian Trail Health & Air Quality project.
Emily Gotschalk is a graduate of Christopher Newport University and is working with DEVELOP at NASA Langley Research Center as an independent research consultant.