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Montreal Protocol Commitments


The Road to Montreal

1950’s Canadian scientists’ interest in ozone monitoring resulted in the Canadian development of the Brewer ozone spectrophotometer to measure UV reaching the earth’s surface.

Dobson units measure the concentration of ozone.

1 Dobson unit (DU) = 1mm pure ozone compressed at standard temperature and pressure at sea level. Holes really thinner areas – in the ozone layer are defined by contours measuring thickness less than 220DU.

In 1964 John Hampson, with Canadian Armaments and Research Development Establishment, noted the potential for ozone damage due to rocket and high-flying aircraft water-vapour emissions. Thoughts re supersonic aircraft and nuclear weapons kept the discussion going for a decade.

Ref: Solar UV in our World (2002) ACER and Environment Canada www.acer-acre.org.

Two articles published simultaneously and independently in 1974 added a new dimension to the problem of ozone depletion:

  • In the Canadian Journal of Chemistry, Richard Stolarski and Ralph Circerone at the University of Michigan described a process in which chlorine from rocket exhausts could catalyze the destruction of large amounts of ozone in the stratosphere over a period lasting many decades.
  • In Nature Magazine, Mario Molina and Sherwood Roland at the University of California had similar concerns but suggested that a much larger source of the chlorine causing catalyzed ozone loss was from human activity namely the many widely used industrial chlorofluorocarbons (CFC’s) that could migrate to the stratosphere. Here they would eventually break down as a result of exposure to intense ultraviolet radiation and release significant quantities of chlorine.

Society apparently faced a choice:

  • Preserve the integrity of the ozone layer which prevents biologically destructive level of UV from reaching the earth’s surface.
  • preserve the economic benefits provided by CFC’s a valuable and otherwise benign group of chemicals with broad applications including refrigeration and manufacture of foams and electric components.

Ecosystem and human health risks were large and unprecedented. Economic costs in abandoning CFC’s also appeared considerable. There was no empirical evidence of ozone loss in the stratosphere.

In 1975, W.C.Wofsey, M.B. McElro, and Y.I Yang of Harvard University, showed that bromine used in fire retardants was also a potent destroyer of ozone.

Ref: Solar UV in our World (2002) ACER and Environment Canada www.acer-acre.org.

For the next decade scientists around the world continued to research these theories to understand the chemical processes. Scientists wanted to look at and to verify implications of impact, natural variability of concentrations and detection of human-caused disturbances. The issues grew more complex and difficult to model, especially with computer limitations.

In 1977 UNEP hosted an international conference on the ozone issue. ‘ World Plan of Action on the Ozone Layer’. UNEP was given the responsibility of promoting and coordinating international research and data gathering activities. In 1978,the USA, then Canada, Norway and Sweden and eventually the European Union banned non-essential aerosol sprays containing CFC’s. Meetings, to build the framework of the agreement, were held in Stockholm 1982, Toronto 1983, Vienna 1985 and in Rome, Leesburg and Geneva1986. Canada was one of the first nations to ban the use of CFC’s as an aerosol propellant. Canada is also one of the countries most at risk from ozone depletion.

In 1985 satellite observations confirmed scientists’ hypotheses linking CFC’s and ozone loss over the Antarctic. The extreme ozone losses over the Antarctic are caused by a combination of high concentrations of ozone-depleting substances and unique meteorological conditions in winter and early spring.

Severe ozone losses occur in the Arctic polar region during extremely cold winters. Polar ozone losses are part of the global ozone loss. The Arctic ecosystems already suffering from the impacts of climate change are extremely vulnerable.

In 1986 the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) released their first major ozone assessment. CFC’s 11 and 12 and other substances that could deplete stratospheric ozone were identified. Identifying these other extremely powerful substances as greenhouse gases also had serious implications for global warming and climate change.

The 1987 signing of the international protocol in Montreal reflected the success of the scientists in reducing the range of uncertainty and in building a compelling case for action.

The agreement included chemicals that were to be controlled, their use, production, consumption, and timing of the implementation, choice of the base year for monitoring and further research, extent of the controls, and arrangements for developing countries.

Ten Years After Signing of the Montreal Protocol

Tracking the ozone amounts from 1987-1997 continued to show a decline in ozone values. In the spring of 1997, however, the typical spring depletion was exceptionally large in the Arctic. This was likely due to the unusual upper wind and temperature patterns that may be, in turn, related to the effects of increased concentrations of greenhouse gases.

Looking to the Future from 1997

If all parties follow the Montreal protocol, the peak of chlorine concentration should be reached in a few years and the decrease could be expected to return to its natural concentration of 1.0 ppb by 2100.

At the present time our models generally underestimate the amount of ozone depletion that has actually occurred. The present models cannot, at the present time, accurately simulate all aspects of ozone distribution with altitude, location and time of year.

The inaccuracies in modeling show that there are gaps in our knowledge of ozone chemistry and atmospheric dynamics, especially in chlorine and bromine induced depletion.

It is now fairly certain that increased concentrations of greenhouse gases causing stratospheric cooling. The cooler the Arctic stratosphere, the greater the ozone destruction which allows more UV to reach the earth’s surface where UV helps to make smog.

Ref: Solar UV in our World (2002) ACER and Environment Canada www.acer-acre.org.

The implications of ecological interactions and other environmental stresses in connection with these increased UV effects, especially biological effects on ecosystems and human health have yet to be explored in detail.

The recovery of the ozone layer, as a response to a decrease in greenhouse gas concentrations since the implementation of the Montreal protocol, needs to be monitored. More research work must be done to understand the complex chemical interactions in the processes that drive the atmosphere.

Developing better tools for modeling which increases the accuracy of prediction of the response of our atmosphere to the presently known greenhouse gases will help us with future disturbances.

Excerpts from

On the 10th Anniversary of the Montreal Protocol

Ozone Science: A Canadian Perspective on the Changing Ozone Layer Summary Environment Canada 1997

See also www.acer-acre.org – Solar UV in Our World ACER and Environment Canada 2002

See Activities in – Check Ontario websites, newspapers and magazines for updated information on new initiatives or reports which show awareness and response to these international recommendations. Research to discover other present and proposed changes.

Eg. Montreal Protocol –
Track Ontario’s history of making changes to meet this agreement – eg freon in air conditioners both in vehicles and buildings and refrigerators.