I work on an experiment that began when the
Bee Gees’ Stayin’ Alive was at the top of the charts. The
project is called AGAGE, the Advanced
Global Atmospheric Gases Experiment, and I’m here in Boston, Massachusetts
celebrating its 35-year anniversary. AGAGE began life in 1978 as the
Atmospheric Lifetimes Experiment, ALE, and has been making high-frequency,
high-precision measurements of atmospheric trace gases ever since.
At the time of its inception, the world had
suddenly become aware of the potential dangers associated with CFCs
(chlorofluorocarbons). What were previously thought to be harmless refrigerants
and aerosol propellants were found to have a damaging influence on
stratospheric ozone, which protects us from harmful ultraviolet radiation. The
discovery of this ozone-depletion process was made by Mario Molina and F.
Sherwood Rowland, for which they, and Paul Crutzen, won the Nobel Prize in
Chemistry in 1995. However, Molina and Rowland were not sure how long CFCs
would persist in the atmosphere, and so ALE, under the leadership of Prof. Ron Prinn (MIT) and collaborators
around the world, was devised to test whether we’d be burdened with CFCs in our
atmosphere for years, decades or centuries.
 |
| Fig 1. The AGAGE network |
 |
| Fig 2. Mace Head station on the West coast of Ireland |
Thanks in part to these measurements, we
now know that CFCs will only be removed from the atmosphere over tens to
hundreds of years, meaning that the recovery of stratospheric ozone and the
famous ozone “hole” will take several generations. However, over the years,
ALE, and now AGAGE, have identified a more positive story relating to atmospheric
CFCs: the effectiveness of international agreements to limit gas emissions.
The Montreal Protocol on Substances that
Deplete the Ozone Layer was agreed upon after the problems associated with CFCs
were recognised. It was agreed that CFC use would be phased-out in developed
countries first, and developing countries after a delay of a few years. The
effects were seen very rapidly. For some of the shorter-lived compounds, such
as methyl chloroform (shown in the figure), AGAGE measurements show that global
concentrations began to drop within 5 years of the 1987 ratification of the
Protocol.
 |
| Figure 3. Concentrations of methyl chloroform, a substance banned under the Montreal Protocol, measured at four AGAGE stations. |
Over time, the focus of AGAGE has shifted. As the most severe
consequences of stratospheric ozone depletion look like they’ve been avoided,
we’re now more acutely aware of the impact of “greenhouse” gases on the Earth’s climate. In response, AGAGE
has developed new techniques that can measure over 40 compounds that are
warming the surface of the planet. These measurements are showing some
remarkable things, such as the rapid growth of HFCs, which are replacements for
CFCs that have an unfortunate global-warming side effect, or the strange
fluctuations in atmospheric methane concentrations, which looked like they’d
plateaued in 1999, but are now growing rapidly again.
The meeting of AGAGE team members this year has been a reminder of how important this type of meticulous long-term monitoring is. It’s also a great example of international scientific collaboration, with representatives attending from the USA, UK, South Korea, Australia, Switzerland, Norway and Italy. Without the remarkable record that these scientists have compiled, we’d be much less informed about the changing composition of the atmosphere, more unsure about the lifetimes of CFCs and other ozone depleting substances, and unclear as to the exact concentrations and emissions rates of some potent greenhouse gases. I’m looking forward to the insights we’ll gain from the next 35 years of AGAGE measurements!
This blog was written by Dr Matt
Rigby, Atmospheric Chemistry Research Group, University of Bristol.
 |
| Matt Rigby |