The Ozone Bio-indicator Garden Project: A Cooperative Effort Between ARMN, Arlington County, NASA, and Harvard

By Jane Metcalfe, Louis Harrell, Nicolasa Hernandez, and Barbara Hoffheins

ARMN has been working with Arlington County, NASA, and the Harvard Smithsonian Center for Astrophysics Science Education to build and maintain a “bio-indicator” garden as part of a project to monitor the impact of ozone air pollution on plants. Bio-indicator gardens consist of plants that exhibit a typical and verifiable response when exposed to ozone air pollution. This project is part of a NASA-sponsored network of ozone bio-indicator gardens across the U.S.—and internationally—in conjunction with its the TEMPO (Tropospheric Emissions: Monitoring Pollution) mission.

TEMPO will be the first space-based instrument to monitor major air pollutants across the North America continent every daylight hour at high spatial resolution. Data collected from the garden over a period of three or four years will be merged with data from other gardens across the country. The mission’s ultimate aim is to monitor the air we breathe with greater detail and precision. This information can be learned from monitoring the plants chosen for the project.

In addition to the overall mission, what are the goals of this ozone bio-indicator garden and what information will it collect?

The Ozone Garden has several goals:

•           To illustrate visually the impacts of ozone pollution on plants

•           To educate all ages about air pollution in Arlington

•           To connect individual actions, as well as official policy, to local air pollution

•           To better understand the impact of ozone air pollution on plants.

Understanding the impact of ozone air pollution will be achieved by merging Arlington data with data from across the country. Data will be collected from all participating gardens using a standard procedure and reported to a project website used by all the gardens. Uniform procedures are critical for data quality.

The TEMPO satellite, which is currently projected to be launched in 2022, will provide very high-resolution hourly data on ozone and will be correlated with data on the impacts to plants in the bio-indicator garden in Arlington.

How concerned are we about ozone in this area?

Ground-level ozone is a harmful air pollutant and is likely to reach unhealthy levels on hot sunny days in urban environments. Ozone can be transported long distances by wind. For this reason, even rural areas can experience high ozone levels. The Washington-Baltimore-Arlington area is one of the country’s most polluted areas due to ozone pollution. The American Lung Association gives Arlington an “F” for ozone pollution from 2016-2018 (the latest information available) ( The American Lung Association also notes that the entire DC area is ranked 20th out of 229 metropolitan areas for high ozone days ( The Environmental Protection Agency currently places the Washington DC area in “Marginal – Nonattainment” for ozone standards (

How did ARMN become involved with the project and where is the garden located?

2018 ARMN trainee, Jane Metcalfe, became aware of the NASA effort in the process of developing a class presentation. She then spearheaded an ARMN Project for an ozone garden and worked with other ARMN volunteers to launch it. The Ozone Monitoring Garden became a true partnership: ARMN developed the project and provided basic funding and volunteers; Arlington County furnished the garden site along with site support, mulch, and fencing; and NASA/Harvard Smithsonian Center for Astrophysics Science Education is responsible for providing genetically-similar plants and seeds, and support for education and outreach.

Walter Reed Community Center in Arlington was chosen for the garden’s site because its conditions were suitable for the plants and it is visible to the community for visits and eventual education events. An area was fenced off and the ground was initially broken and prepared for planting in September 2019. However, an early frost in 2019 prevented the garden from being planted that year and the subsequent pandemic prolonged efforts to continue work on the space. In addition to Arlington, the NASA/TEMPO program directors were unable to get seeds to the 17 gardens across the U.S. and internationally.

Photo of the garden
Photo on March 11, 2020 just before all work stopped with pandemic. Photo courtesy of Kasha Helget.

Has the ozone garden been planted?

Yes! It was determined last fall that planting and monitoring could proceed with Covid-19 safety procedures in place. So, a team led by new ARMN member, Nicolasa Hernandez, along with other members of ARMN and the Master Gardeners of Northern Virginia, began clearing the site on August 7, 2020.

Seeds were planted on October 2, 2020 so they could establish before the first frost of the season. The bed was divided into four areas that were outlined with mulch paths. Individuals can walk on the mulch paths to get a close look at the plants without disturbing them. They can later inspect the plant leaves for evidence of any elevated presence of ozone. 

Photo of volunteer in the garden
Volunteers Barbara Hoffheins and Todd Minners install seeds and mark walkways on October 2, 2020. Photo courtesy of Nicolasa Hernandez.

The team installed two of the areas with common milkweed (Asclepias syriaca) a local native perennial, the third area with snap beans that are sensitive to ozone (Phaseolus vulgaris ‘S-156’), and the fourth with snap beans that are less sensitive to ozone (Phaseolus vulgaris ‘R-331’).

Below is a photo of the garden three weeks after planting. The first two leaves of each of the snap bean plants are easily visible. These plants should continue to develop through the winter. The seeds planted for the common milkweed (a perennial requiring overwintering) will emerge in late this spring. The weeds that have returned throughout the garden since planting will be removed by the team.

Garden three weeks after planting with visible snap bean plants. Milkweed hadn’t come up yet. The remaining plants are weeds. Photo courtesy of Nicolasa Hernandez.

What will ozone impacts to the plants look like?

Damage caused by ozone is typically observed as stippling or purpling on the top side of older leaves of the plant. If foliar damage occurs on younger leaves, then it is not ozone damage. The team also has to be aware of mimicking symptoms and other pest problems that look like ozone injury.

Later, signposts will be placed in the garden to describe its purpose and identify each area along with photos that indicate the conditions to look for.

As the plants grow, ARMN volunteers will monitor them for physical effects of ozone pollution and report the results to the national database.  

What is the future plan for the ozone garden?

ARMN volunteers will need to keep the garden weeded, and plan to install additional seeds this spring.

ARMN, via the Virginia Master Naturalists, has applied for a grant from Harvard to pay for signage to explain the project and how it links to TEMPO. A public education program is planned so that members of the community will be able to see the link between ozone and plant health. Additional procedures will be developed for people who will be monitoring the garden.   

For more information about the TEMPO Citizen Science program, see:

Finally, thanks go out to the ARMN Ozone Bioindicator team for their hard work and dedication in the development and care of this Ozone Garden: 

  • Sonya Dyer
  • Mary Frase
  • Louis Harrell
  • Nicolasa Hernandez
  • Barbara Hoffheins
  • Phil Klingelhofer
  • Jane Metcalfe
  • Todd Minners
  • Marj Signer

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