Ozone – a silent peril at ground level

Robyn Francis reports, March 2012

We learned of the importance of ozone in the stratosphere when it depleted to allow harmful levels of ultra-violet rays to reach the earth’s surface, so ozone up there is a good thing, but not so good closer to earth in the troposphere. At ground level ozone is killing trees and forests and damaging human health. A silent killer that needs to be urgently addressed.

I recall Bill Mollison in the late 1980’s warning about the hazards of low-level ozone as a major degenerative factor for life on earth, but along the way it’s been overshadowed by concerns for Green House Gases (GHGs), especially CO2, and their climate change impacts.  Ironically, the chemical pollutants that cause ozone at ground-level are also very potent green house gases as they rise up into the atmosphere, and are also major contributers to acid rain.


So what is ground level ozone?

Ground-level ozone, the main component of smog, is formed when volatile organic compounds react with pollutants from burning fossil fuels, motor vehicle exhaust, reactive nitrogen from agriculture, and methane, in the presence of UV radiation and heat from the sun. Ozone at ground level is a toxic poison – especially to plants and also to people.

In Australian cities: “The chemicals that react to form ozone come from sources such as: motor vehicle exhaust, oil refining, printing, petrochemicals, lawn mowing, aviation, bushfires and burning off.  Motor vehicle exhaust fumes produce as much as 70% of the nitrogen oxides and 50% of the organic chemicals that form ozone.” – DSEWPC


What does it do to plants?

It enters the stomata of leaves as they take in CO2 for photosynthesis, it impairs plant growth and ability to take up nutrients. With cumulative exposure, plants are subject to a range of problems eventuating in death, and the worst impact is on trees that are slowly dying around the world.

Common symptoms of ozone poisoning include:

  • Stippled, singed foliage with marginal burn
  • Chlorosis, a loss of pigment from reduced photosysnthesis
  • Yellow needles in conifers, thinning crowns
  • Cracking, splitting , corroded, oozing and stained bark
  • Early leaf senescence (maturing and aging), premature leaf drop in autumn
  • Loss of autumn colours and vibrance
  • Holes, cankers, breaking branches
  • Absence of terminal growth
  • Rampant lichen growth

Ozone weakens trees immune systems and impairs their natural defences against insects, disease and damaging fungi. It makes their wood more brittle. Root systems deteriorate as trees expend more energy to repair ozone damage in their leaves – this is compounded by acid rain. The breakdown of root systems makes trees more prone to falling in storms and increases the risk of landslides and avalanches.

I have seen the above first hand. In 2009 travelling through the Cascade Mountain in the USA North West, the number of unhealthy trees in the forests was quite distressing.

The photo on the right shows a group of trees with dying growth tips and excessive amounts of lichen up the trunks and along limbs.

I was told a beetle is triggering the dieback of trees, and locals wonder if climate change is a trigger, however after researching the issues surrounding ground level ozone, it would appear that the beetles are a symptom of a deeper and wider problem. 

The following year, 2010 I was in Europe and the demise of Chestnut trees was brought to my attention, initially in South Germany, however throughout my travels in Germany and France every Chestnut tree I saw was sick. A colleague returning from Ukraine said the Chestnuts were sick and dying there and throughout much of Europe. These are issues now, not pending problems of some distant future scenario.

These chestnut trees in Sth France should be green in their summer prime, but it looks more like early autumn with yellowing and browning leaves, infested with a deadly rust disease – an example of premature senescence.

Ozone also reduces the growth and yield of crop plants, and impairs their ability to take up nutrients. This in turn means people and animals are suffering from nutrient deficiencies.


What does ground-level ozone do to us?

Ozone impacts most severely on people who suffer asthma emphysema and respiratory illness, who are at greatest risk of dying during severe heat waves  with high UV and ozone levels. Athletics and joggers are particularly cautioned as they breathe more deeply. Ozone has been linked to diabetes, cancers, heart disease, ADHD, Alzheimer’s, and autism.

High amounts of ground-level ozone causes

  • airway irritation, coughing, and pain when taking a deep breath;
  • wheezing and breathing difficulties during exercise or outdoor activities;
  • inflammation, which is much like a sunburn on the skin;
  • aggravation of asthma and increased susceptibility to respiratory illnesses like pneumonia and bronchitis; and,
  • permanent lung damage with repeated exposures.



How Can I Reduce My Contribution to Ground-Level Ozone?

Some suggestions from GroundLevel Ozone – National Safety Council


• Avoid idling your motor vehicle.

• Conserve energy and recycle.

• Do not refuel your vehicle or lawn mower on ozone alert days. If you must refuel, do so after dark—remember that sunlight assists ozone-forming reactions.

• Keep your vehicle well tuned.

• Limit driving; carpool, walk, ride a bicycle, and combine trips.

• Start charcoal (e.g. for barbeques) with an electric lighter or newspaper instead of lighter fluid.

• Use public transport.

 I think we can easily add many more actions to this list, and most of the things we can do as individuals to reduce our carbon footprint and minimise green house gas emissions will also help reduce the creation of ground-level ozone.

 A far too common sight in the Cascade Mountains, lots of dead and dying trees in the forest.

A far too common sight in the Cascade Mountains, lots of dead and dying trees in the forest.


Remember Acid Rain?

It’s alive and well despite being largely forgotten since it hit the headlines in the second half of the 1980’s when trees in the famous Black Forest started dying.  Acid Rain is caused mainly by the sulphur dioxide and nitrous oxides emitted by burning fossil fuels, especially coal. Motor vehicle exhaust also contributes to acid rain.

Emissions of SO2 and NOx in industrialized countries have been and will continue to be reduced, but not eliminated, region by region. Meanwhile, other parts of the world will continue to contribute to acidic atmospheric deposition, at a magnitude even larger than occurred during the 20th century. Thus, there is a ‘‘wave’’ of acidic atmospheric deposition-induced acidification moving across the landscape, leaving behind a ‘‘wake’’ of ecological damage that can linger for 2–6 decades (e.g., Cosby et al., 1985; Alewell et al., 2000), even centuries (Blake et al., 1999). Acidic atmospheric deposition is a common regional problem and will continue to be until Earth’s fossil-fuel resources have been depleted or until humankind develops alternate methods to produce sufficient energy for its ‘‘energy hungry’’ population.

Acid rain is big enough a problem in its own right, and for trees and forests, it compounds and exacerbates the problems arising from ground-level ozone.


Nitrogen pollution

“‘It’s been said that nitrogen pollution is the biggest environmental disaster that nobody has heard of.” Alan Townsend warns at a conference in Feb 2012.

“Awareness has grown, but nitrogen pollution remains such a little-recognized environmental problem because it lacks the visibility of other kinds of pollution,’ Townsend explained. ‘People can see an oil slick on the ocean, but hundreds of tons of nitrogen spill invisibly into the soil, water and air every day from farms, smokestacks and automobile tailpipes. But the impact is there – unhealthy air, unsafe drinking water, dead zones in the ocean, degraded ecosystems and implications for climate change. But people don’t see the nitrogen spilling out, so it is difficult to connect the problems to their source.'”

“…nitrogen inputs to the terrestrial environment have doubled worldwide during the past century. This increase is due largely to the invention and widespread use of synthetic fertilizer, which has revolutionized agriculture and boosted the food supply.

“The concern focuses on so-called ‘reactive’ nitrogen. Air contains about 78 percent nitrogen. But this nitrogen is unreactive or ‘inert’, and plants can’t use the gas as a nutrient. In 1909, chemist Fritz Haber developed a way to transform this unreactive gas into ammonia, the active ingredient of synthetic fertilizer. By 2005, human activity was producing about 400 billion pounds of reactive nitrogen each year.”

‘A single atom of reactive nitrogen can contribute to air pollution, climate change, ecosystem degradation and several human health concerns.”

“Though the full extent is currently unknown, nitrogen pollution can impact human health. Reactive nitrogen is a key contributor to air pollution, including the formation of ground-level ozone, which is a well-known health risk. Recent estimates suggest that nitrogen-related air pollution costs the U.S. well over $10 billion per year in both health costs and reduced crop growth. And though less well studied, high nitrogen levels in water can cause a variety of health concerns, ranging from the effects of drinking water nitrate to the potential to alter the risks of several human diseases.”

“Demand for nitrogen fertilizers is increasing in response to growing human population, improving diets, and expanding biofuel crop production. Unfortunately, only about half of the applied nitrogen is used by crops, and the rest is unintentionally released to groundwater, rivers, and to the air, where it presents problems for human health and ecosystem health. Burning fossil fuels for industry and transportation also releases nitrogen into the air, which falls on soils and water bodies.”

“The nitrogen gas that makes up most of the Earth’s atmosphere is inert, with little impact on ecosystems. Nitrogen converted to its reactive forms such as NH3 and NOx, however, can cause profound biological changes.  Activities such as fertilizer manufacturing, intensive livestock production and the burning of fossil fuels convert nitrogen to these reactive forms which can then enter and potentially over-fertilize ecosystems. This can lead to problems such as algal overgrowth in lakes, reduced water quality, declines in forest health, and decreases in aquatic and terrestrial biodiversity by favoring ‘nitrogen loving’ species at the expense of other species with low nitrogen preferences.”

Above quotes about Nitrogen pollution are from Alan Townsend, Ph.D. ecology and evolutionary biology professor at the University of Colorado at Boulder


PHOTOS: Robyn Francis

SOURCES and further reading:





Leave a Reply