Plants and air pollution

As someone who grew up in the San Fernando Valley of Los Angeles in the 1960s and 70s, I am no stranger to air pollution. I recall days when we had to stay indoors at school because the air quality was so bad. And, no, we did not have air conditioning. It was terrible. Luckily, I had a great 6th-grade teacher, Ms. Melching. She would dim the lights and read to us about blizzards. It helped. But the polluted air gave us headaches and respiratory problems.

Smog in Utah, 1950 (CDC) Public Domain

Plants need clean air to grow and thrive too. But it can be hard to recognize the damage caused by air pollution. It often looks like a disease, heat stress, mite feeding, nutrient disorders, or water stress. If you can rule those problems out, consider air pollution.

Types of air pollution

Air pollution is estimated to cost US agriculture over one billion dollars annually. This damage can be chronic or acute. The smoky yellow skies from fires or fumes from a chemical spill fall are acute forms of air pollution. More likely, your plants are feeling the effects of long-term exposure to low levels of pollutants from industry, power generation, and vehicles.

​The most common pollutants include nitrogen oxides, ozone, peroxyacetyl nitrate (PAN), and sulfur dioxide. Ammonia, chlorides, chlorine, and fluorides may also be in the mix choking your plants.

​Symptoms of air pollution

Depending on the type and age of each plant, the time of year, humidity levels, temperatures, and the chemicals involved, symptoms of air pollution can vary. There are three basic types of damage: leaf tissue damage, color changes, or growth problems.

​Damage from air pollution can include bleaching, blossom drop, browning needles, leaf tip burn, mottled foliage, premature leaf drop, reduced yields, stunting, twig dieback, and yellow leaf edges. These injuries occur on new foliage more than on older leaves.

​The most common signs of some of the major pollutants are as follows:

Air pollution damage on tomato (Mary Ann Hansen, VPISU, Bugwood.org) CC BY 3.0

• Chlorine damage looks similar to sulfur dioxide and fluoride damage with the addition of streaking.
• Ethylene is a plant hormone used in ripening. The ethylene produced by cars and trucks causes a failure of buds to open (called “sleepiness”), blossom drop, downward leaf curling, poor development, and stunting.
• Fluorides can cause yellow mottling and tip burn with a distinctive narrow dark brown band between the healthy and damaged tissue. Early fruit fall may also occur.
• Ozone is the most important US air pollutant. It causes bleaching, bronzing, early leaf drop, flecking, leaf rolling, mottling, reduced bud formation, scorching, stippling, and stunting.
• Peroxyacetyl nitrate (PAN) is the second most toxic air pollutant. It causes banding, bleaching, bronzing, chlorosis, early leaf drop, and silvering.
• Sulfur dioxide causes beige, reddish brown, or black papery blotches. Bleaching and chlorosis may also occur.

Ozone damage to maple (Robert L. Anderson, USDA Forest Service, Bugwood.org) CC BY 3.0

Tip burn after 4-hours of 6.5ppm of ozone (USDA Forest Service, Bugwood.org) CC BY 3.0

Protecting your plants

Healthy plants can protect themselves better, so keep them well-fed and watered. Also, the damage occurs most often during warm, humid days with no wind. Monitor air quality in your area and give your plants a light shower from the hose on days with poor air quality.

You can also help your plants (and yourself) by learning about the industries currently or recently active in your area (or upwind). And think about how you spend your money. Are you supporting companies that protect the environment or opting for cheap stuff?