Some good news about the ozone layer

Kim Strong gets at the roots of climate change

Let’s begin with something positive — over the next 20 years or so, the global ozone layer should recover to the state it was in before the infamous Antarctic ozone hole was first sighted in the 1980s. That’s assuming we humans continue to phase out the harmful chlorofluorocarbons (CFCs) that created the ozone hole in the first place.

How are scientists able to predict this recovery?

In the same way that they were able to detect the depletion of the ozone layer — with spectrometers and computers.

Over the past 15 years, U of T physicist Kim Strong has built a reputation as a leading innovator in the use of spectrometers to measure gases from CFCs in the atmosphere. “Specifically, we measure the absorption or emission of light in the atmosphere by gases. By looking at the strength of the absorption or emissions, we can then work out the concentrations of the gases.”

And it’s the concentrations of the gases in CFCs that have caused the depletion of the ozone layer — the protective shield invented by nature that keeps the sun’s harmful ultraviolet rays from burning up life on Earth. The ozone layer protects humans against such harmful effects as skin cancer and cataracts, while also preventing UV radiation from damaging ecosystems, and reducing the degradation of materials used in our physical infrastructure.

Meanwhile, the warming of the climate is causing ice to melt at the poles and is changing everything from the destruction of polar bears’ natural home on the Arctic ice to a possible eventual rise in ocean water and flooding of low-lying locations such as Manhattan. Climate change also has links to the recovery of ozone. Unravelling the interactions between ozone and climate is a topic of considerable interest in the global scientific community.

Strong and her colleagues use a variety of spectrometers in various settings — at the Atmospheric Observatory on U of T’s downtown St. George campus and 4,000 kilometres to the north at the Polar Environment Atmospheric Research Laboratory at Eureka, Nunavut.

Her team has also put spectrometers on balloons that have traversed much of the atmosphere above the Earth (a recent grant to physics professor Kaley Walker will enable her and Strong to resume the balloon program over the next few years). And, finally, Strong utilizes spectrometer measurements of the atmosphere from satellites, which provide a global picture of atmospheric composition.

But how do the scientists control their spectrometers?

“Computers are essential to our measurement research. Some of our spectrometers at Eureka, for example, are fully automated. So we can reset the commands for what we need the instrument to do by way of a computer in Toronto.”

The Strong team also relies on computing to analyze the vast amounts of data the spectrometers measure over spans of many years. “When we use these instruments, it’s not like taking a small sample and doing a chemical analysis. We’re looking at radiation from the sun and atmosphere and how it interacts with gases. This is complex physics and you need a good model to see how the interaction happens. Computers are essential for this level of complexity. You can’t use a paper and pencil to retrieve gas concentrations from atmospheric spectra.”

And computers enable the scientists in Strong’s lab to interpret their measurements. The pollutants the Strong team analyzes come from all over the world, borne on winds that might take carbon monoxide from a forest fire in Siberia or coal-fired plant in Ohio to the various levels of the atmosphere. “So, you need more than just measurements in Toronto or Eureka. That’s when it’s valuable to compare measurements with simulations from various models. You need powerful computing to do that.”

Back to that ozone recovery. While scientists predict that this will happen during the 21st century, it may be a bumpy road getting there. Last year, for example, Arctic ozone depletion was bigger than ever before. While this was something of an anomaly, resulting from an unusual mix of conditions, Strong notes that continued atmospheric measurement of gases remains essential for understanding the forces acting on the ozone layer and monitoring its recovery.

“We’re not out of the woods yet. The atmosphere can surprise us sometimes. That’s why I want to be doing these measurements using the instruments and computing power we have. I want to know if the atmosphere is going to do what we expect it to do — or is it going to do something different? If we’re not watching, how will we know?”