Learn More About Ozone

Ozone is a gas made up of three oxygen molecules (O₃) that is found in two layers of the atmosphere that surrounds the Earth: The stratosphere (“good” ozone) and the troposphere (ground-level or “bad” ozone). Ozone in the stratosphere, 12-19 miles above the ground, forms naturally and shields the Earth from harmful solar radiation. Ozone that forms at ground-level is an air pollutant and is dangerous to breathe.

Unlike some sources of air pollution, ground-level ozone isn’t emitted directly from a source such as tailpipes or smokestacks. Ground-level ozone forms when two types of pollutants, nitrogen oxides (NO_x) and volatile organic compounds (VOCs), react in sunshine. The highest ozone levels are typically found in the afternoon on hot, calm, sunny days, although ozone can be found year round.

Ozone enters plant leaves through tiny pores on the underside of the leaves (stomata). Keeping stomata open is necessary so that the plants can get carbon dioxide from the air, which they turn into sugars for food during a process called photosynthesis. At the same time, however, ozone also gets inside the leaf and damages parts of the leaf cells that make the sugars. This can ultimately reduce the growth of the plant, reduce the production of wood and fruits and vegetables in timber and crop plants, and decrease the amount of carbon stored in plant tissues.

Plants are able to protect themselves from ozone damage in several ways. For example, antioxidants, like vitamin C, can protect against ozone damage, so plants with more antioxidants are less susceptible to ozone damage. Also, plants protect themselves by closing their stomata to reduce the amount of ozone getting inside their leaves. Plants close their stomata for other reasons, like when they are stressed by drought, and this also helps to protect the plant against ozone damage. Plants that have smaller and fewer stomata are typically less susceptible to ozone damage because less ozone enters the leaf.

Ground-level ozone causes muscles in the lungs to contract, narrowing pathways that carry air into and out of the lungs and making breathing difficult. Exposure to high ozone levels can cause a sore throat, coughing, lung inflammation, and permanent lung damage. Ozone decreases lung capacity by anywhere from 15 to more than 20 percent in sensitive individuals, and is particularly harmful to children, elderly, and people with respiratory illnesses. Similarly, animals (pets, livestock, wildlife) can also experience reduced lung functioning.

Ground-level ozone pollution is also hazardous to plants, damaging plant cells and destroying leaf tissues. This reduces the plant’s ability to produce its own food through photosynthesis, decreasing the amount of food that agricultural crops produce, the amount of wood that trees produce, and the amount of carbon dioxide that plants remove from the atmosphere. It also weakens the plants and can make them more susceptible to disease, pests, cold, and drought. One study found that nine billion dollars of U.S. corn and soybean crops were lost each year to ozone between 1980 and 2011.

Ozone damage on sensitive snap bean plants.

We need to cut down on our use of fossil fuels, reduce the amounts of VOCs emitted, and generally use less energy. This includes:

• Making smart transportation choices: Choose a low-pollution vehicle, drive less (combine trips, carpool, work from home, bike, walk, or take public transportation), keep your car properly tuned, don’t idle for longer than 30 seconds, refuel in the evening, and stop fueling at the first click.
• Taking action at home: choose renewable energy, choose low VOC products, use electric-powered lawn and garden tools, mow in the evening, and forgo the fire on days with poor air quality.

Since we know that ozone is bad for human health and our ecosystems, scientists are working to better understand where ozone sources (NO_x and VOCs) are coming from and how they move through the atmosphere. This will help us understand how to lower ozone levels to keep human and ecosystem health safe.

Until recently, ozone measurements have been limited to stationary monitors, or satellites that can only measure any given spot once a day. For example, the Environmental Protection Agency has set up monitoring stations across the U.S. that are capable of tracking the variation in ozone levels for the surrounding areas. However, there are still large areas within the U.S. and throughout the world without ground-level ozone monitoring equipment. Recent advances in technology now allow us to measure ground-level ozone from space.

One example is a new satellite mission called TEMPO, Tropospheric Emissions: Monitoring of Pollution, which revolutionizes how we measure tropospheric ozone. A collaboration between NASA and the Smithsonian Astrophysical Observatory, the TEMPO instrument monitors major air pollutants, including ozone and many of the chemicals that form ozone, across North America from a geostationary vantage point. In other words, it stays at a fixed position approximately 22,000 miles above the Earth’s equator constantly staring down at North America. Unlike most existing air quality monitoring satellites which provide once-daily measurements, TEMPO provides hourly data at high spatial resolution. In fact, TEMPO can distinguish between areas of 10 square kilometers, a region a little smaller than the Los Angeles International Airport. And TEMPO isn’t alone in revolutionizing how we monitor air quality. It is one of three instruments that will make up a geostationary air quality constellation measuring air quality every daylight hour around the Northern Hemisphere. The other instruments include South Korea’s GEMS (Geostationary Environment Monitoring Spectrometer), and the European Space Agency’s Sentinel-4. This means that many people will know the quality of the air in their neighborhood.

Ozone sensitive plants can help detect ozone pollution in areas that are not currently being monitored by instruments. A public garden that includes these plants gives us an easy way to understand air quality through a connection with nature. In regions with poor air quality, you can see the plants transition from green and healthy to spotted and unhealthy over the course of the summer. When visiting ozone bioindicator gardens in our network, you can observe and record damage to ozone-sensitive plants within the garden, helping scientists to better understand the causes and consequences of ozone pollution to plants.

Curious if ozone concentrations in your neighborhood are high? Ozone bioindicators may be more common than you think, and you can plant some in your own yard. Try planting one of the known ozone bioindicator species identified by the U.S. National Park Service. You can also check out your nearest EPA ozone monitor if you live in the U.S.

If you have a public space and would like to join our garden network, please fill out this Google form.