By Barbara Hoffheins
Overview
The ARMN Ozone Bioindicator Garden continues for a fourth year at Walter Reed Community Center (WRCC). ARMN has been working with Arlington County, NASA, and the Harvard Smithsonian Center for Astrophysics Science Education in building and maintaining the bioindicator garden as part of a nationwide project to monitor the impact of ozone air pollution on plants. The plants in the garden consist of varieties and cultivars that exhibit a typical and verifiable response when exposed to ozone air pollution. They are provided by the Ozone Garden Network, which is affiliated with the National Science Foundation, NASA, Harvard University, and the Smithsonian Institution.
The plants are genetically identical in all of the Network gardens. The observations of ozone effects on plants in the ozone gardens add to the understanding of ground-based ozone seasonal patterns, distribution, and intensity. Elevated ozone levels can seriously damage crops and forests and cause respiratory damage or distress in humans and animals. (For more background on this project, see earlier blog articles about the mission, installation, maintenance, and information collection concerning the garden in February and November, 2021; September, 2022; and September, 2023.)
At WRCC we have two varieties of snap beans (Phaseolus vulgaris), one variety of potato (Solanum tuberosum), two tobacco varieties (Nicotiana tabacum), Cutleaf Coneflower (Rudbeckia laciniata), and Common Milkweed (Asclepias syriaca). The specific varieties of snap beans, potatoes, and tobacco have been studied by ozone researchers for many years. The Ozone Garden Network provided two new posters to display at the ozone garden to convey more information about its purpose, and NASA’s new satellite for monitoring air pollution in North America.
Ozone Garden team members participated in two community events so far this year. The first was on March 9, the 2024 Plot Against Hunger Spring Garden Kickoff, sponsored by Arlington Friends of Urban Agriculture at the Arlington Central Library. Team members Jon Bell, Anne Doll, and I were invited to give a presentation about the Ozone Garden. Jon delivered a compelling introduction featuring the famous photograph, “Earthrise” taken by astronaut William Anders on December 24, 1968, on NASA’s Apollo 8 Mission. Earthrise is said by experts to have been the inspiration for the environmental movement. Anne and I discussed the garden’s history, selection of plants, and what ozone damage looks like. We made several interesting connections at this event. These led to: planting ozone sensitive beans at the Highlands Urban Garden (HUG) (next to the Virginia Department of Environmental Quality (VA DEQ) air monitor at the Arlington Fire Station in Virginia Highlands Park); and sharing ozone indicator plants with Dr. Susan Agolini, a professor at Marymount University, who is establishing an ozone bioindicator garden on the university grounds. We also gave away ozone sensitive potatoes from the ARMN garden for attendees to plant in their gardens. Last year’s potato yield from the ozone garden was sufficient for team member, Todd Minners, to donate about 10 lbs. to a food bank and for me to ship potatoes to the Ozone Garden Network to distribute to other ozone gardens.
The second event was on July 23 for the 55+ group at WRCC at which I gave a talk about the ARMN garden. ARMN’s Bill Browning attended, and we used the opportunity for a quick chat about his work to address deer overpopulation in Arlington. Although attendance was small, it made for a cozy, informal discussion and the audience had a lot of questions. I presented slides about the history and rationale for the garden, NASA’s involvement, and what ozone damage looks like. Afterwards, we visited the garden and looked for ozone damage.
There is also a lot going on in the ozone garden itself. In May, team members Todd Minners, Jon Bell, and I prepared the garden beds for planting. The garden consists of three 4’ x 8’ raised beds constructed with notched corner blocks to hold 2” thick boards that form the sides of the beds. Over time, the corners weakened and some of the top boards started to fall out. Exacerbating this is the ingrowth of long bald cypress roots from a nearby tree that year by year increases the shade in the garden. Todd and Jon wrangled the roots and shored up the blocks. There is concern that, in years ahead, the bald cypress roots and shade might force a decision to relocate the garden. Ozone damage needs sun plus volatile organic compounds (mostly from automotive exhaust in Arlington), as well as long, hot, dry days. However, increasing shade on the garden each year might protect some of the plants from ozone damage and also retard growth. (Incidentally, unlike the WRCC garden, the Marymount University garden, mentioned earlier, is in a more open area with heavy traffic. It will be interesting to see if plants in that garden will show heavier ozone damage than those at the WRCC garden.
Two photos below show patterns of suspected ozone damage on plants in the WRCC garden this year. Spots on the tobacco leaf are called weather fleck that is caused by air pollution. The black spots on the Cutleaf Coneflower are also associated with ozone damage from pollution. So far, no ozone damage has been observed on the snap beans at WRCC this year. However, a photo of a snap bean leaf from the HUG garden taken on August 7 shows the classic ozone damage patterns of brown spots in between the leaf veins. This is likely because these leaves receive direct sunlight for many hours each day and experienced elevated ozone levels recorded on August 1 and 5. The white spots and rusty blotches on the snap bean leaves are signs of disease not related to ozone damage.
Cutleaf Coneflower leaf photographed July 18, 2024. Photo by Barbara Hoffheins.
The VA DEQ air quality monitor, which is also coordinated with EPA’s constellation of air quality sensors, has recorded nine days so far with ozone readings at or above the EPA’s exceedance level of 70 parts per billion (ppb) ozone in air. This is the level considered hazardous to human health. An example is a chart below from the Aurora Hills sensor on June 14, 2024, when the ozone level was at 70ppb or higher for about four hours. (The VA DEQ site also provides Current Air Quality and Forecast for the various sites around the state, along with possible pollutants, cautions, and risk groups.)
Screenshot July 14, 2024, at 2.25.05 PM (Aurora Hills DEQ sunsor ozone reading).If the ozone level stays above 70 ppb for eight hours or longer, it is recorded as an event at this VA DEQ site. One of these exceedance events was recorded on June 14 in Northern Virginia (but not Arlington).
An exciting development is the availability of data from NASA’s satellite, Tropospheric Emissions: Monitoring of Pollution (TEMPO), which was launched in early 2023. At the TEMPO website, a user can select the Data drop down menu to access TEMPO data for the public or scientists. In the For Public screen, the user can input a zip code in the “Location” box and select a date to view nitrogen dioxide (NO2) levels during the daylight hours. (At present, the public data view does not show ozone levels, but NO2 is a precursor to the formation of ozone if other environmental conditions exist.) A vertical bar at the right of the map indicates relative concentrations of NO2, with black at the top corresponding to undesirably high levels. There are controls to zoom into a neighborhood level, select time of day, and lighten the overlay of color blocks representing NO2 concentration levels. As an example, the figure below is a zoomed in view of the locations of the ARMN Ozone Bioindicator Garden and the VA DEQ sensor.
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