A team from the National Center for Atmospheric Research made an ozone garden full of sensitive plants that react visibly to air pollution. These sensitive plants don't die, but their leaves get evenly spaced black spots before falling off when ozone in the air gets exposed to sunlight. This visual reaction is an indication of the quality of air in the area.
These sensitive plants include cutleaf cornflowers, milkweed, potatoes and snap bean. This reaction does take some time, depending on how long the ozone is in the air for and how long the plants have been exposed. While ozone in the air doesn't typically affect humans directly, it can result in reduced crop yields and slower tree growth in some parts.