The Really Big Ozone Story: Plants With Asthma

April 2, 2008

Most news about ground-level ozone pollution focuses on its considerable impacts to human health. But there may be a far broader and potentially bigger story: Ground-level ozone pollution significantly impairs plants' ability to absorb CO2 - which in turn exacerbates climate change, reduces agricultural yields (think: food shortages), and damages ecosystems.

Plants breathe, too — taking in carbon dioxide and putting out oxygen, the reverse of the way humans and animals breathe. Plant respiration is one of the globe's largest "carbon sinks." Just as ground-level ozone can damage human lung tissue, impairing our ability to take in oxygen, plant tissue also can be damaged. The results: Stunted or slower plant growth, greater susceptibility to disease, and overall reduced CO2 intake and oxygen output.

A May 2007 report from MIT's Global Change Joint Program brings the big picture into focus. Lead author: John Reilly, 617-253-8040.

Reilly was interviewed in a segment in the Mar. 14, 2008, edition of Living on Earth. He explained why ozone pollution can be particularly damaging to crop yields: "We're usually fertilizing crops, and fertilizing crops is getting them to grow really fast. It's like us going out and working really hard, or running really hard. So if you do that and then you have high ozone levels at the time, the damage to crops can be larger than unfertilized vegetation. ...We found that [there] could be as much as a 50 to 60 or 70% yield decline in temperate regions in China, the US, and Europe."

This means that reporters in agricultural regions might want to look at a different set of ozone benchmarks to turn air pollution and climate change into a local economic story. Said Reilly: "There is a threshold, 40 parts per billion of ozone in the atmosphere, above which damage starts occurring. What really happened here is that the actual ozone levels only increased 50 percent, but when measured above this threshold, the amount of ozone increased by six-fold. So that was a dramatic increase and led to this high damage."

A similar study, published in Nature, July 2007, points out that because of plant impacts, ozone might be twice as big a contributor to climate change as originally estimated.

Study (subscription required for full text access). Lead author: Peter M. Cox, Univ. of Exeter (UK).
BBC coverage, July 25, 2007.

EPA's new ozone standard, published Mar. 27, 2008, cites impacts to vegetation (especially crops) as a key rationale.

More coverage, SEJ Tipsheet, Mar. 5, 2008.

Ozone pollution can come from seemingly unlikely places, including composting operations for agricultural and food waste. The March 2008 issue of BioCycle reports that in CA, "air quality districts in several regions of the state are considering regulations that require green waste composters to reduce emissions of Volatile Organic Compounds (VOCs), which react with other chemicals in the air to produce ground level ozone."

The BioCycle story cites an emissions-profiling study being conducted by the California Integrated Waste Management Board (CIWMB) at the Modesto, CA, composting facility.

More information about how, where, and when VOCs are emitted from large composting operations could help curb ozone pollution. Brenda Smyth, project lead, CIWMB: 916-341-6605.

Rice - a staple food for most of the world's population - could be especially hard-hit by ozone pollution. USDA scientist Elizabeth Ainsworth recently told the New Scientist that "ozone concentrations of around 60 parts per billion, which have already being recorded on farms in China and the US, cause [rice] yields to drop by 14%. ... New varieties of rice, bred to tolerate high ozone and increased temperatures, are urgently needed." Contact Ainsworth: 217-265-9887.

While ground-level ozone pollution tends to be highest in urban areas and along highways, over time it spreads out, increasing the background level of ozone nearly everywhere. Forests, even remote ones, can be affected. There's been little research into this angle so far. However, US Forest Service Region 8 (Southeastern states) has developed a downloadable forest ozone calculator software (Windows only).

Additional information on ozone levels in remote locations is available here. If you want to look at ozone in national parks, where ozone is often as high as or higher than in cities, starting points are NPS' Ozone Monitoring Overview and Ozone Standard Exceedances in National Parks (especially at bottom, see pdf for "Ozone 3 Year Rolling 4th Highest Daily Max Average"). You can find more detail by first identifying monitors in national parks, then getting data for each monitor here.