In this NASA image from Sept. 2006, the Antarctic ozone hole was equal to the record single-day largest area of 29.5 million square kilometres. The so-called hole is a region where there is severe depletion of the layer of ozone - a form of oxygen in the upper atmosphere that protects life on Earth by blocking the sun's ultraviolet rays. The blue and purple colors are where there is the least ozone, and the greens, yellows, and reds are where there is more ozone. (NASA/Associated Press)

Ozone

Ozone, a bluish gas composed of three oxygen atoms, is harmful to breathe, but absorbs ultraviolet radiation that harms living organisms. The discovery of the depletion of the ozone layer in Earth's stratosphere the 1980s was the motivating factor behind the Montreal Protocol restrictions on the use of CFCs.

Last week in Montreal, representatives from the governments of almost 200 countries agreed to speed up the elimination of hydrochlorofluorocarbons, or HCFCs, a greenhouse gas that also depletes ozone.

The meeting of the United Nations Environment Programme (UNEP) came on the 20th anniversary of the Montreal Protocol, the international agreement lauded for reducing worldwide production of chlorofluorocarbons, or CFCs, by 95 per cent.

CFCs were seen as a major cause of depletion of the ozone layer, the upper atmospheric blanket that shields us from some of the harmful ultraviolet radiation from the sun.

Twenty years later, policy-makers targeted HCFCs, the very substance many companies switched to when CFCs were banned. In an agreement reached Friday, the member nations agreed to freeze production and consumption of HCFCs in 2013 and accelerate the plans for a final phase-out.

Here we take a look at HCFCs, their impact on the environment, and what the new deadlines mean for industrialized and developing nations.

What are HCFCs?

They're compounds consisting of the elements hydrogen, chlorine, fluorine and carbon. For years they have been used as a refrigerant in air conditioners and fridges and as a propellant for blowing foam insulation, among other industrial uses.

How do HCFCs and CFCs differ?

The Montreal Protocol phased out almost all production of CFCs in industrialized nations in 1995, with developing countries having a deadline of 2010. As a result, many companies switched to using HCFCs, which studies showed were less harmful to the ozone layer.

The problem with both compounds is the chlorine, said Parisa Ariya, an atmospheric chemistry professor at McGill University. When CFCs or HCFCs enter the stratosphere, the radiation in the atmosphere breaks down the molecules, releasing chlorine. And chlorine destroys ozone, Ariya said.

"A molecule of chlorine can destroy 100 molecules of ozone, so even a little can have a big effect," she told CBC News. Bromine, an element used in combination with fluorine and chlorine in fire extinguisher agents, is also harmful to ozone molecules.

CFCs are considered the more dangerous than HCFCs because they interact so little with the lower atmosphere, meaning more particles rise to the stratosphere, where they can do more harm. The presence of hydrogen atoms in HCFCs make them more likely to mix with the lower atmosphere and break down chemically before they reach the ozone layer, said Ariya.

How else do HCFCs harm the environment?

HCFCs and hydrofluorocarbons (HFCs) — another compound favoured by industry as a CFC replacement in 1987 — are also potent greenhouse gases, contributing to the warming of the planet as carbon dioxide does. But the effect of many kinds of HCFCs and HFCs on global warming is much more pronounced than an equivalent amount of CO₂.

The production of one form of HCFC (called chlorodifluoromethane) has been blamed for the creation of a byproduct called fluoroform (HFC-23). Fluoroform's impact on global warming is 11,700 times greater than the impact of an equivalent mass of carbon dioxide, according to the U.S. Environmental Protection Agency.

Why the rush to eliminate HCFCs?

In August 2006, the UN Environment Programme said the ozone layer could return to pre-1980 levels over much of the world by 2049, but it would take until 2065 to restore the shield over Antarctica.

The reduction of CFCs, halons (which contain bromine) and HCFCs in the last 20 years has been credited with bringing the ozone layer back. The hole over Antarctica is slightly smaller than the 29.5 million square kilometres it reached last year, according to the latest information from the UN's World Meteorological Organization, released in September.

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That's the good news. But a number of attendees in Montreal, including government representatives from Canada and the United States, wanted to speed up the ban on HCFCs because alternatives that have no effect on the ozone layer and less impact on climate change - such as hydrocarbons - already are being used in industry.

The UNEP agreement pushed ahead the deadlines for both industrialized and developing countries.

Developed countries have agreed to reduce production and consumption by 75 per cent by 2010 and by 90 per cent by 2015 with final phase-out in 2020. Developing countries have agreed to freeze production in 2013, cut production and consumption by 10 per cent in 2015, by 35 per cent by 2020 and by 67.5 per cent by 2025, with a final phase-out in 2030.

Environment Minister John Baird said before the conference that a speedy reduction of HCFCs is a way to kill two birds with one stone.

"Although the world is on track to fully eliminate HCFCs, speeding up the phase-out would allow us to simultaneously address two of the most critical issues facing our planet today — ozone preservation and climate change," Baird said.

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