2004
Blue Planet Prize
Dr. Susan Solomon (U.S.A.)
Senior Scientist,
Aeronomy Laboratory, National Oceanic andAtmospheric Administration

Air on Gaia:
The earth is wrapped with arobe. Thanks to it, we are able tosustain our daily activities. From
some point in time, human activities went too far impairing it. In
2004 the opening film instilled
us with a hint to consider the
future of the global environment,
the ways toward developmentthat enables us to sustain theenvironment.

Dr. Gro Harlem Brundtland(Norway)
Chairman WCED (World Commission on
Environment and Development)
Former Prime Minister of Norway
Director-General Emeritus, WHO

145

Their Imperial Highnesses
Prince and Princess
Akishino at the Awards
CeremonyHis Imperial Highness Prince Akishino congratulates the laureates
Dr. Hiroyuki Yoshikawa,chairman of the Selection
Committee explains therationale for the determinationof the year's winners

The prizewinners receive their trophies from Chairman Seya

Hiromichi Seya,chairman of theFoundationdelivers the
opening address

Dr. Gro Harlem Brundtland

The prizewinners
at theCongratulatory
Party.

Howard H. Baker Jr., Ambassadorof the United States of America toJapan and Age Bernhard Grutle,
Ambassador of Norway to Japan,
congratulate the laureates○

146

Dr. Susan Solomon

Profile

Dr. Susan Solomon
Senior Scientist,
Aeronomy Laboratory, National Oceanic and Atmospheric Administration

Education and Academic and Professional Activities
1956
Born on January 19 in Chicago, Illinois
1977
Bachelor of Science degree in chemistry at the Illinois Institute of Technology
1981
Doctoral degree in chemistry from the University of California, Berkeley
1981
Research Chemist, the Aeronomy Laboratory of the National Oceanic andAtmospheric Administration (NOAA)
1985
Adjoint Professor, Department of Astrophysical, Planetary and Atmospheric
Sciences, University of Colorado
1988
Program Leader, Middle Atmosphere Group of the Aeronomy Laboratory,
NOAA
1990-present Senior Scientist, Aeronomy Laboratory, NOAA
1992-present Member, National Academy of Sciences
1995-present Foreign Associate, French Academy of Sciences
2000
American Meteorological Society Carl-Gustaf Rossby Research Medal
2000
National Medal of Science

The ozone hole over Antarctica attracted a high degree of interest among the global environmental issues in the late 20th century due to concerns that stratospheric ozone layer depletion
would increase the amount of harmful ultraviolet light on earth. Prior to the discovery of the
Antarctic ozone hole, theories suggested that the ozone layer might be depleted by a few percent in a century, but the issue came to the fore with the dramatic discovery of a much larger
and rapid depletion. Dr. Solomon was the leading scientist in identifying the mechanism thatcreated the Antarctic ozone hole. She and her colleagues put forth a theory involving heterogeneous chemical reactions of chlorine on the surfaces of the particles found in very cold
clouds in the Antarctic stratosphere. She then conducted observations in Antarctica over two
expeditions in 1986 and 1987, and succeeded in providing key evidence for her theory. This
research played a leading role in identifying the process by which the surfaces of clouds produced by the extremely low temperatures of Antarctica couple with increased atmosphericchlorine due to human use of chlorofluorocarbons (CFCs) to deplete ozone at unprecedented
rates. Dr. Solomon's findings provided one of the scientific cornerstones for the amendmentsof the Montreal Protocol leading instead to a ban on CFCs beginning in 1990, and thus contributed significantly to the protection of the ozone layer.

147

After studying chemistry at the Illinois Institute of Technology, Dr. Solomon majoredin atmospheric chemistry at the University of California, Berkeley, where she received her doctoral degree in 1981. After her graduate work, she joined the National Oceanic andAtmospheric Administration, and she has continued her research on the atmosphere there eversince.
In the mid 1980s, it was revealed that a dramatic depletion of the ozone over Antarctica
had been detected in the springtime from September to October beginning in the late 1970s.
The ozone depletion was very extensive in both space (covering the entire Antarctic continent)
and magnitude (up to about half of the ozone was depleted in comparison to pre-1970 levels).
Dr. Solomon became deeply interested in these findings, and presented a theory hypothesizing the causes of depletion based on heterogeneous chemical reactions involving the unusual
clouds that are created under the atmospheric conditions of extremely low temperature ofminus eighty degrees Celsius, specific over Antarctica (polar stratospheric clouds).
Dr. Solomon theorized that the reaction of hydrochloric acid and chlorine nitrate, which
does not occur significantly in the gas phase, might take place extremely rapidly on the icy surfaces of the particles in the polar stratospheric clouds, thereby producing nitric acid and chlorine. She further hypothesized that as the sun first rose with the arrival of spring in Antarctica,
the chlorine would dissociate through photolysis, producing reactive chlorine atoms andrelated molecules such as chlorine monoxide and chlorine dioxide. These reactive forms ofchlorine destroy the ozone with dramatic efficiency. Dr. Solomon's theory is consideredgroundbreaking not only for identifying the mechanisms that produced the chlorine radicals
directly related to ozone depletion, but also for explaining the high concentration of reactive
chlorine compounds in the atmosphere.
At the end of August 1986, chosen as the leader of the observational expedition team at
the tender age of thirty, she set out to Antarctica aiming to verify the existence of ozone holeand clarify the mechanism of its formation. The team measured the ozone depletion by several
methods, and they also measured key chemicals that gave insight into the cause. The measurements of active chlorine revealed that there was approximately a hundred times more of
the substance than could be explained through gas-phase chemistry. This finding was a definitive indication of the involvement of heterogeneous chemistry as put forth in Dr. Solomon's
theory. The following year, she led a second expedition to Antarctica, where the team foundthat the depletion of the ozone had worsened compared to the previous year.
Dr. Solomon has authored two books as well as having written or co-written over 150
papers. In her most recent book, The Coldest March, she wrote about the tragic expedition ofa team led by British explorer Robert Falcon Scott, who succeeded in reaching the South Polebut perished on their return. Through extensive studies of the records from the expedition andmore recent meteorological data, Dr. Solomon investigated the reasons for their demise andillustrated that their downfall was brought on by the rare misfortune of exceptionally frigid climate conditions. Further, she provided throughout the book a wonderful account of the individual explorers of the Scott team as they trekked through Antarctica, bringing to life their personalities, challenges, and legacies.
As a scientist, Dr. Solomon is deeply interested in making a contribution to society, and148

values the important role that science can play in areas such as environmental issues. Throughthe application of science, she continues to work towards protecting the society from the dangers that arise from ignorance by shedding light on the nature and reasons for environmental
problems.

149

EssayEnvironmental Issues and Science:
Some Thoughts on Roles and Stages
Dr. Susan Solomon“Believe one who has proved it. Believe an expert.” Virgil, in the Aeneid.
What is the role of science in environmental issues? Most people would readily agree
that presentation of the best possible technical information is the obvious answer. But how
does it preserve that status? How does it best communicate it to non-specialists?
Science can be the light of the world. In my opinion, it lights the world best when it isframed in a broader context of the other diverse challenges and inputs to societal change.
What can reasonably be considered to be fact is one side of this. It is also important to consider
where facts begin to fade into the genuine role of opinion, and the non-scientific elements ofsocietal choices.
Consider the application of this line of thinking to the issue of ozone depletion. The
depletion of the ozone layer over Antarctica and its chemical cause is now well-establishedthrough numerous independent measurements. There is no debate about the time scale of thegases that are responsible. The chlorofluorocarbons that cause the ozone hole live in the atmosphere for decades to centuries depending upon the species, so any effects that occur will lastfor many years. The elements of scientific understanding progressed quickly in the case ofozone depletion, from the initial ideas of the mid-1970s to the discovery of the Antarctic ozone
hole in the mid 1980s and demonstration of its cause within a few years. Technology was also
quick in the development of efficient and effective substitutes for nearly all applications, which
include refrigeration, air conditioning, and foam blowing among others.
It is clear that a reduced ozone layer leads to more ultraviolet light at the ground. There
are no significant winners from more ultraviolet light; rather there are risks to ecosystems, andto human health. There are matters unrelated to physical science involved when the issue of
how large a risk to society or to ecosystems is acceptable or unacceptable is considered. But
there can be little debate that increased risk of skin cancer and cataracts are serious matters to
those who may end up contracting such health problems. Thus the potential impacts were alsoeasy to describe and readily understood by the public and policymakers alike.
A wise colleague has noted that there are three stages to any environmental issue: credibility (is the change real? Can we prove why it is happening?); manageability (what are theoptions for dealing, or not dealing, with the changes and what would be the outcomes?); andfinally accountability (have the options been effectively implemented, and are the desired outcomes occurring). In the case of the depletion of the ozone layer, the credibility stage began in
the mid-1970s when the issue was first brought to global attention and it progressed rapidly,
particularly following the discovery and explanation of the unexpected Antarctic ozone hole.

150

Between about 1985 and 1990 there was swift and convincing scientific demonstration of avery large effect and its explanation.
The manageability stage started in about the late 1970s, when international actions
began to consider phaseouts of chlorofluorocarbons, at least in some applications such as spraycans. Substitutes first began to be used for the molecules responsible for the depletion.
Policies accelerated quickly following the success of the credibility stage in demonstrating
increasing clarity connecting observed changes to chlorofluorocarbons. By the late 1990s,
agreements were in place globally, and production of the chlorofluorocarbons and halons thatcause ozone depletion had dropped dramatically. But the ozone manageability stage involved
more than science. It also involved economics, public policy, values, and technology, all as elements in the mix of influences. And in my own view, science lights the world best when it isacknowledged that these aspects go beyond its purview. That’s not to say they are not important or that they do not draw in part upon science, but they clearly also involve different considerations to which science is an input but not the sole determinant. I would suggest that science provides the best service to society and the best credibility for the scientific process whenthese distinctions are clear.
Each scientist involved in such issues has a challenge to consider in deciding upon theway he or she will deal with the components of the problem that go beyond their expertise, andin deciding which matters go beyond scientific evidence into the realm of values and personal
opinion. Some people ask if it’s difficult, or even if it is possible, to separate scientific evidence
from opinion. I don’t believe it is difficult at all for a good scientist to do this – in fact it is fundamental to what scientists do each and every day as they weigh what they can say from a careful analysis of information, and separate that from what they wish were known. It is a fundamental aspect of the scientific process and the scientific ethic that has been a bedrock for
hundreds of years of research across every field of scientific endeavour. History holds innumerable demonstrations of how effectively this has functioned in the past. Today is no different, nor are environmental issues different.
Now we’re mainly in the accountability stage for ozone, the stage of understanding
whether the chlorofluorocarbons are decaying as they should be due to reductions in production of CFCs worldwide, and whether the ozone layer is hence recovering as it should.
Important progress has already been made, as observations worldwide have confirmed that theabundances of many of the chemicals responsible for ozone depletion are declining. This stage
is not expected to progress to completion quite so swiftly, because the chemicals in question
will remain in our atmosphere for many decades as already noted. The rate of ozone depletion
has certainly slowed down, and it’s fair to say that the ozone layer has at least stabilized on
average. Perhaps it’s helpful to think of the analogy with a person having a disease that has
been making them progressively sicker and sicker each year. The first sign of progress is notgetting worse anymore, and the next is genuine improvement, a start on the path to recovery.
That step may be happening at certain altitudes and latitudes, and is probably just around thecorner for the global ozone layer.
Unlike many other environmental pollution issues, the chlorofluorocarbons that are
causing ozone depletion are often used in applications where they are intended to be largely

151contained, such as refrigerators, air conditioners, and foams: It is the leakage of the gases outof these ‘banks’ that causes release to the atmosphere. It has recently been suggested that there
is probably more chlorofluorocarbon remaining in ‘banks’ worldwide than was thought. Slowreleases of these ‘banks’ would be expected to increase future ozone depletion above what it
would otherwise have been. So a new scientific issue for the accountability period is to understand how much material is scattered throughout the world and how much leaking is occurring.
A new policy and manageability question is therefore whether to consider further steps tolimit releases from banks. An interesting analogy is also whether to more deeply consider thefate of current and future banks of other molecules – such as hydrofluorocarbons now used as
substitutes for the chlorofluorocarbons in many applications. The hydrofluorocarbons don’t
deplete the ozone layer but they do contribute to climate change, and their use as substitutes insuch applications implies a growing bank. So the understanding gained in this stage has linkages to another environmental issue. This reflects the success of policy regarding ozone depletion, which has virtually eliminated the use of these molecules in emissive applications suchas spray cans, and has led to greater and greater care in containment of the gases in applications where it is precisely the containment that is the goal (such as in an air conditioning system). Perhaps ironically, the increased attention paid to avoiding emission implies a shift thatchallenges policy. Whereas use of such molecules in emissive or very leaky ways implied agreat deal of emission but a limited bank, as emissions have been reduced and attention to environmental issues has led to less and less leaky systems, the new issue that arises is the fate of
the banks that will therefore be built up through continuing production. Containment coupledwith continuing use implies a buildup of a bank – and a new challenge for policy in considering not just what is emitted now but what is in the bank and how much of that may be emitted(or not emitted) in future.
Now I’d like to briefly turn to the issue of climate change. The carbon dioxide that is theprimary cause of climate change lives in our atmosphere for more than a century. Such a long
lifetime implies that each generation’s choices about emissions of carbon dioxide will affectthe climate of many future generations. We may choose to make different choices about risking something if we know that if we make a mistake we can put it back the way it was in a few
months versus a case where it takes centuries or more to restore.
Scientific information also provides strong evidence for a substantial human influenceon current climate. In addition to a warmer climate (by about 0.6°C on average over the 20th
century), there is also evidence for other changes, such as increased heavy rainfall and changes
in circulation patterns. How “dangerous” are climate changes now and in the future, and forwhom, is a question increasingly being asked.
Research on the impacts of climate change is an active field. There is debate about themagnitude of the impacts and the degree to which adaptation can occur. Some evidence suggests that there could be both winners and losers. There is also debate about technologies andcosts. In climate change today, the world is deeply immersed in both the credibility and manageability phases. They are occurring more strongly in parallel than they did for the ozone
issue, in part because of the realization brought about by the story of ozone that long timescales are involved in reversing any changes once they are observed.

152

So one factor that we as a global society are now wrestling with is how to balance ourscientific confidence in human effects upon how climate is changing or may change in the
future as well as the impacts of those changes with the fact that if any changes do happen
they're going to be with us for many decades – they will not be easily or quickly reversed, andthat's a key dimension in our changing view of environmental risk, which involves perspectives
as well as science. People take out individual health, fire, or flood insurance by considering themagnitude and duration of consequences along with assessment of the magnitude of the risk.
Even if every risk could be well defined and quantified, different people are likely to have different perceptions of acceptable levels of risk – for themselves, for their children, and for
future generations. It is sometimes asserted that the climate change problem is terribly complicated, and that poor communication with the public occurs as an inevitable result. But perhaps the complication lies not with the science but with its role in the broader backdrop ofquestions of risk and world views. As societies wrestle with the credibility and manageabilityof the climate change issue, a key challenge for science is to illuminate the evidence and therisks as clearly as possible, while recognizing that science is one input among several to a challenging set of policy questions.
Acknowledgement. I would like to thank Daniel L. Albritton for helpful discussions,particularly the three stages of credibility, manageabiliity, and accountability.

153Lecture

Ozone Depletion and Climate Change:
A Personal Journey from Pole to PoleDr. Susan Solomon
1. Introduction
I am honored and humbled to receive this wonderful award. I thought that the best way to show
my deep appreciation for this great honor would be to try to make this lecture something thatwould reflect the Asahi Glass Foundation’s wise commitment to advancing environmental
understanding, particularly the understanding of how environmental changes can reach beyond
national borders, beyond generations, and sometimes beyond the edge of scientific imagination. The story of the depletion of the ozone layer involves many phases: phases of matter(gas, solid, and liquid), phases of scientific discovery, and phases of public awareness andglobal policy decisions. I will touch upon all of those phases in telling you of my own part in
the story of Antarctic and global ozone depletion. A broader review citing the many important contributions by other scientists worldwide can be found in Solomon (1999). Finally, inclosing I will briefly present personal reflections on some parallels and differences between
ozone depletion and climate change issues.
Stratospheric ozone represents a layer of vital protection for life on the earth’s surface,because it shields the planet from harmful ultraviolet light in a way no other atmospheric molecule can. Yet ozone is easily attacked by other chemicals, as was underscored in the 1970s
when concerns began regarding the possibility of ozone depletion due to chlorofluorocarbons(CFCs). At first, this came as a surprise since chlorofluorocarbons were known for their largely
unreactive character at low altitudes, giving safety and stability when used in applications asdiverse as blowing of insulating foams, refrigeration, and as propellants in spray cans.
Although the chlorofluorocarbons have lifetimes in our atmosphere ranging from about half acentury to as many as several centuries depending upon which gas is considered (CFC-11,
CFC-12, CFC-113, CFC-114, CFC-115, etc.), these seemingly benign gases can transformthrough chemistry, leading to massive ozone loss. This led to changes in scientific thinking
and a related challenge to policy: heightened recognition that human beings sometimes makechemicals that can affect our environment over a period far outlasting the generation that produced them. Similar issues arise for a number of greenhouse gases (see Table 1), a point thatwill be discussed further below. How much ozone depletion could these long-lived CFCs produce? Through what chemistry? Where in altitude and latitude?

154

Table 1: Atmospheric lifetimes (years) of selected chlorofluorocarbons and non-chlorofluorocarbon greenhouse
gases

Chlorofluorocarbons
CFC-11
CFC-12
CFC-113
CFC-114
CFC-115

Non-chlorofluorocarbon greenhouse gases
45
100
85
300
1700

Carbon dioxide
CH4
N2O
SF6
CF4

≈150
12
114
3200
50000

Chlorofluorocarbons are not stable everywhere: as they rise up into the stratosphereabove about 10-15 kilometers, photochemical processes driven by harsh sunlight break themdown to produce chlorine atoms. A portion of these chlorine atoms can be converted to safe
reservoirs such as chlorine nitrate and hydrochloric acid, making the partitioning of chlorine
between specific chemicals (Cl versus HCl, for example) of paramount importance to theimpact on ozone. Insofar as the released chlorine is converted to relatively unreactive reservoirs such as HCl for example, ozone depletion is limited, but insofar as the chlorine remains
in more reactive forms such as Cl, ozone can be destroyed by catalytic cycles. Much of mywork has focused on the ways that chlorine partitioning can be radically affected by surface
reactions involving solids and liquids, leading to far greater ozone destruction than previously
thought.
The ozone chemistry understood prior to the mid-1980s all involved reactions of gas
molecules with one another and with sunlight: it was believed that ozone depletion was driven by chemical reactions occurring exclusively in the gas phase. That chemistry was
expected to lead to maximum ozone loss in the rarified air of the upper stratosphere, on theupper side of the ozone layer near 40 kilometers. By 1983, a United States National ResearchCouncil report projected that continued use of chlorofluorocarbons at then-current rates would
probably lead to depletion of the total global ozone layer by about 3% in about a century.
Some argued that this was a small effect, far in the future, and subject to large uncertainties arguments that are frequently echoed today in discussions of global warming.
2. Poles Apart: The Unexpected Ozone Depletion At the Ends of the Earth
2.1 The Antarctic Ozone HoleIn the mid-1980s, a remarkable change in understanding of ozone occurred when scientificwork at the bottom of the world documented an unprecedented and unexpected depletion of
Antarctic ozone, restricted to the spring season. Ozone appeared to be depleted not by a few
percent but by about a third, not in the far future but just a few years after the NRC said little
would occur for a century. It was a surprise to many that these initial observations came from155

ground-based methods at isolated research stations on the world’s coldest continent. It wasquickly realized that an error in data analysis approaches had impeded the satellites from seeing what the ground-based stations had documented so thoroughly through years of dedicatedeffort.
Only three sites on the vast continent at the bottom of the world have archived long-termhigh-quality measurements of ozone since at least the 1970s: the British station at Halley, theJapanese station at Syowa, and the American station at the South Pole. Figure 1 shows the timeseries of October mean total ozone measurements provided by those three stations. The
British data display less variability than the others from year to year, so that as early as 1985 it
was clear that ozone was behaving strangely at Halley. A key factor in the observed variability from site to site is the movement of the southern polar stratospheric vortex. At both poles,
wintertime cooling leads to very cold conditions at high latitudes, while considerably warmer
conditions prevail at lower latitudes. This temperature gradient in turn is linked to a vast windsystem that encircles the cold polar air, a vortex. But the vortex can be disturbed by atmospheric waves, similar to the waves that move weather systems across both hemispheres, gracing the images in television weather forecasts. The British station at Halley is located inside
the cold Antarctic vortex more often than the Japanese station at Syowa, which sometimes displays ozone levels characteristic of air outside the vortex. The frequency and intensity of thesewaves play substantial roles in determining the inter-annual variability of ozone concentrationand ozone loss both locally (e.g., Syowa versus Halley) and on the larger scale (from one year
to another inside the vortex).

Figure 1. October monthly mean total ozone records (in Dobson Units) from Halley (upper left), Syowa (upper
right), and the South Pole (lower right); the data are available at the World Ozone and Ultraviolet Data Center. A
satellite ozone map for September 6, 2000 is also shown (courtesy NASA). The satellite map shows that Syowa
is located very close to the edge of the vortex on this particular day.

156

At Syowa station and at the South Pole, measurements of the vertical profile of theozone depletion in the 1980s suggested anomalous behavior in Antarctic spring at a specificand surprising range in altitude. The change was occurring not at the very top of the ozone
layer near 40 kilometers as expected from gas-phase chlorine chemistry, but at an entirely different height range from about 10-20 kilometers, just where the most ozone is to be found (seeFigure 2). This move of the center of action is why about a third of the total ozone was being
depleted then, and today the depletion often exceeds half of the total integrated total ozone
layer. It was clear that this ozone depletion was not just larger than what had been imagined,
but totally different in character. A massive change in scientific understanding was needed to
explain this change in ozone depletion from global to polar, and from 40 kilometers down to
10-20 kilometers.

Figure 2. October ozone profiles are shown at the latitude of Syowa station (left), averaged for 1965-1976 showing a normal ozone layer observed before the ozone hole developed, as well as the averages for 1980-1990 and
1994-2003, illustrating the progressive deepening of the ozone depletion there. Model calculations are presented
in the right hand panel, where the percent ozone depletion versus altitude derived from the data are compared tomodels including surface chemistry, as first presented in Solomon et al. (l986) and updated to present from themodel presented in Portmann et al. (l996).

2.2 A New Mechanism of Antarctic Ozone Depletion
My colleagues and I suggested that an entirely different kind of chemistry might be responsible for the ozone hole: not gas-phase chemistry but surface reactions (also called heterogeneous reactions). We suggested that these could occur on the icy polar stratospheric clouds thatform in the extremely frigid conditions of Antarctica in winter and spring, at altitudes near 1020 kilometers. In particular, we noted that the densities of chlorine species capable of catalytically destroying ozone could only be appreciably enhanced at these key altitudes if boththe HCl and ClONO2 reservoirs were severely reduced, and we suggested that this could occur
through the following reaction occurring via surfaces of polar stratospheric clouds:

157

HCl + ClONO2 → HNO3 + Cl2
The Syowa ozonesonde data were among the observations that helped our developmentof this new picture. Figure 2 shows the October mean ozone profile measured at Syowa overvarious time periods, along with our early model calculations as presented in Solomon et al.
(l986) and updated model calculations we described a decade later (Portmann et al., 1996).
Our early model did not extend below about 18 kilometers, nor did it include all of the chemical cycles that are now known, but our suggested surface chemistry did capture the mostessential features of the process, particularly the movement of the ozone loss region down from40 kilometers to the very heart of the ozone layer.
Why does the ozone loss occur in October, rather than earlier in the Antarctic winter?
We emphasized that one more step was needed: such a process could not deplete ozone until
sunlight was also available (e.g., to dissociate molecular chlorine, Cl2). Thus, we suggested
that surface reactions could render chlorine from chlorofluorocarbons much more damaging
towards ozone than had been imagined based on gas phase chemistry, that those surface reactions would occur most effectively in Antarctica because of cold conditions that lead to stratospheric clouds, and that rapid ozone destruction occurred in spring when sunlight returned tothe polar cap (Solomon et al., 1986). This surface chemistry implied large perturbations not
only to Cl2 and Cl, but also to a suite of related chlorine molecules that interchange rapidly
among each other (including chlorine monoxide, ClO and chlorine dioxide, OClO) and canengage in rapid ozone destruction. It is now nearly two decades since the Antarctic ozone
hole was discovered, and in that time a series of measurements of many different chemicals has
confirmed this change of phase from gas to surface chemistry (see references in Solomon,1999).
2.3 Observational Evidence: Verifying the Role of Chlorofluorocarbons and Surface
Chemistry
In 1986, I was privileged to lead an expedition to the Antarctic that was able to make some of
the first measurements that tested this chemistry, involving four different research groups.
Here I’ll focus on the measurements that my own group carried out of ozone, nitrogen dioxide, and chlorine dioxide. Chlorine dioxide was a particularly important early measurement
because that molecule is proportional to Cl and ClO, and its detection could provide a directindication of whether or not polar stratospheric clouds were indeed liberating chlorine. The
proposed surface chemistry also converts reactive nitrogen to nitric acid, which impedes thereformation of ClONO2 and thereby further enhances the ozone loss. This reduces nitrogendioxide concentrations and makes that molecule a critical indicator in the chemistry as well.
Indeed, as we emphasized in Solomon et al. (l986), the products of the surface chemistry are
as important as the reactants. Finally, observations of ozone itself using visible light from theground were useful in verifying the ozone hole reported by other methods such as the ultraviolet absorption method used at Halley, Syowa, and the South Pole.
We used a spectrograph to collect light from the sun, the sky, and the moon, and ana-158

lyzed the spectrum in wavelengths from about 400 to 450 nm (blue light) to search for the distinct fingerprints of absorption due to ozone, nitrogen dioxide, and chlorine dioxide, whichremove as little as a few percent or even a few tenths of one percent of the incoming light, making detection a challenge (Mount et al., 1986; Solomon et al., 1987; see also Sanders et al.,
1993; Miller et al., 1999). Like Syowa station, the American site at McMurdo where we did
our work is sometimes under the stratospheric polar vortex and sometimes outside it, so we
sampled both Antarctic and sub-Antarctic air. We were able to arrive at McMurdo in lateAugust before the sun was above the horizon, and hence before substantial ozone loss begins
at that location. One of the stunning experiences of my life in science was to witness the ozone
levels drop at McMurdo during September 1986. Ozone fell from about 300 Dobson Units
when we arrived in Antarctica in late August 1986 to under 200 Dobson Units by late
September, and the disappearance of a third of the total ozone supported the observations ofothers regarding the veracity of the ozone hole and its seasonality. The falling ozone wasaccompanied by a spectacular enhancement in chlorine dioxide (Figure 3). In late August and
September under cold conditions, chlorine dioxide was about 50-100 times greater than gasphase chemistry can explain, so this data pointed towards surface reactions involving chlorine
as the likely cause of the ozone hole. The nitrogen dioxide was in contrast extremely low, as
also expected from polar stratospheric cloud chemistry. As temperatures rose, the chlorine
dioxide disappeared and the nitrogen dioxide increased, again as expected. Thus the seasonal
behavior of both molecules supported the theory of the key role of surface chemistry in perturbing the composition of the Antarctic stratosphere, leading to rapid ozone loss.

159

Figure 3. Daily evening twilight observations of chlorine dioxide (OClO) and nitrogen dioxide (NO2) at McMurdo
Station in 1986, from Solomon et al. (1987) and Mount et al. (l987). Temperatures at 70 mbar (about 18 km) arealso shown for comparison, illustrating the low NO2 and very high OClO in August and September, as well as thelinks of higher NO2 and lower OClO to incursions of warmer air (e.g., around day number 250). As temperatures
warmed in October, OClO disappeared and NO2 increased to typical stratospheric levels.

We made measurements of chlorine dioxide using direct moonlight as well as the scattered light from the twilight sky. Having both the nighttime and twilight measurements was afurther test of the chemistry due to the large diurnal cycle of this molecule, and Figure 4 shows
how differently the nighttime chlorine dioxide behaved in Antarctica compared to what wasobserved by us at other latitudes where polar stratospheric clouds do not occur, for example in
Colorado. In the lunar data, we also measured enhancements of about a factor of 100 above
gas-phase chemistry predictions. Further, as the moon rose or set, we were able to measureits systematic behavior with changing lunar angle. Because the slant path through the atmosphere increases as the moon approaches the horizon, the amount of chlorine dioxide weobserve in the path through the atmosphere to the moon increases in a well-defined way dur-160

ing a night of observations. That provides an important check on the measurements, one that
I have always felt was a simple but elegant way to confirm the data (albeit at times challenging to the observer, particularly when adjusting instruments throughout the frigid Antarctic
night at surface temperatures below -40°C).

Figure 4. Observations of nighttime OClO (top) using the direct light of the moon as a light source. The positionof the moon at our laboratory is shown in the bottom panel. The OClO changes with lunar angle (upper panel), andthe observations at McMurdo systematically followed the expected behavior throughout the night. In contrast,
OClO levels are below the detection limit of the instrument in Colorado in winter as illustrated.

161

2.4 First Measurements in the Arctic
Having seen that chlorine dioxide was greatly enhanced in Antarctica, my colleagues and I
went north to Thule, Greenland in January 1988 to search for enhanced chlorine chemistry
there. Using the moon as the light source, we were able to see the first clear signs that chlorine dioxide was also significantly enhanced in the north compared to gas-phase chemistry(Solomon et al., 1988). The levels of chlorine dioxide that we observed in Greenland that year
were not as large as in the Antarctic. That might be generally expected since the Arctic stratosphere in winter is nearly always warmer than the Antarctic. As in Antarctica, Arctic polarozone loss depends upon the overlap between chemical perturbations due to cold temperatures,
associated polar stratospheric clouds, and sunlight. In recent years, substantial Arctic ozone
depletion has been observed in some especially cold years, but the depletion is not as large asin the Antarctic. A key factor in the difference is that Arctic temperatures nearly always warm
up in spring much earlier than in the Antarctic, limiting the overlap between sunlight and cold
temperatures and cutting off the ozone depletion.
3. New Phases in Understanding Surfaces: Liquid Particles and Volcanoes
At the time of discovery of the ozone hole, it was thought that polar stratospheric clouds werecomposed entirely of solid particles, mainly water ice. But in addition to the solid phase, we
now know that the liquid phase is also important to stratospheric chemistry, and the solid andliquid particles of the stratosphere contain additional chemical species besides water. Indeed,polar stratospheric cloud surfaces can even be composed of supercooled liquids. Liquid sulfuric acid and water particles, and nitric acid hydrates and solutions are part of the family ofvarieties of surfaces that contribute to polar stratospheric clouds. All of these surfaces are now
known to drive much of the same surface chemistry, and this has relaxed the threshold forenhanced ozone loss related to surface chemistry from a picture in which temperatures had to
be extremely cold (to allow water ice to form) to a far more widespread phenomenon affecting latitudes outside the polar regions. A key factor is the availability of water in and on thesurfaces, which affects their reactivity (Hanson et al., 1994; Solomon, 1999). These considerations also appear to have important effects on the interannual variability of polar ozone
depletion, as I will now describe.
By the late 1980s, several scientists began to conduct laboratory studies to examine
whether some of the surface chemistry that takes place on solid polar stratospheric clouds
might also occur on the liquid surfaces that are known to be present throughout much of thelower stratosphere. These are composed mainly of sulfuric acid and water. Further, theirabundances can be greatly enhanced after explosive volcanic eruptions, which can deposit
large amounts of sulfur dioxide at stratospheric altitudes. The sulfur dioxide oxidizes to form
sulfuric acid, which in turn increases stratospheric particle sizes and surface area. My colleagues and I have made several contributions to the understanding of liquid phase chemistry
in the stratosphere, particularly regarding the role of volcanic effects.
Laboratory studies by multiple groups have shown that the surface reaction between
HCl and ClONO2 that is so important on solid polar stratospheric clouds can also occur on liquid surfaces, albeit with a rate that is a strong function of temperature. Other important sur-162

face chemistry can also occur on liquid surfaces (such as the hydrolysis of N2O5 and BrONO2)
and these also enhance ozone depletion.
With several colleagues, I conducted a number of modeling studies of this new liquid
phase chemistry. We first showed that such reactions probably played a significant role in driving mid-latitude ozone loss after the eruption of the Mexican volcano El Chichon in the early
1980s (Hofmann and Solomon, 1989), thereby influencing the early detection of changes innorthern hemisphere mid-latitude ozone due to manmade chlorine. While the discovery andexplanation of the Antarctic ozone hole was important to policy deliberations, the identification and explanation of ozone loss at mid-latitudes probably helped inspire further action by
policymakers to reduce emissions of CFCs. At that time, the future amount of CFCs was projected to continue to increase in the atmosphere, and we postulated that more ozone loss could
occur if a large eruption were to occur in the presence of these increased levels of chlorine. The
eruption of Mt. Pinatubo in the Philippines in 1991 provided a test. Observations revealed
widespread mid-latitude ozone loss after the eruption of Pinatubo in the northern hemisphere.
However, there was no obvious southern mid-latitude ozone loss at that time, an observationthat stands today as a key challenge to present understanding. Nevertheless, observations of
nitrogen dioxide, chlorine monoxide, and other chemicals in both hemispheres do support theview that important ozone-destroying surface reactions indeed occur on liquid surfaces in the
mid-latitude stratosphere following major volcanic eruptions.
My colleagues and I argued that volcanic surfaces can also be important in polar
regions, because there too they can enhance the amount of surface area available to drive thechemistry, making the polar stratospheric clouds even more abundant and effective (Solomon
et al., 1993; Portmann et al., 1996). We suggested that reactions on volcanic surfaces might
have played a very important role in the onset of observable Antarctic ozone loss in the early
1980s, after the eruption of the Mexican volcano El Chichon. We also argued for larger depletions following Pinatubo in the early 1990s, and in the Arctic (Solomon et al., 1996; Solomon
et al., 1998). Figure 5 shows our calculations of how the combined effects of increasing chlorine and modulation of polar stratospheric clouds by volcanic activity probably affected theAntarctic ozone record, enhancing the depletion after the two major eruptions in the early
1980s and early 1990s compared to what likely would have occurred if no volcanoes had
erupted.
Figure 5 suggests that the lives of many scientists, and the evolution of international policy, could have been quite different without the eruption of El Chichon in the early 1980s: itlikely would have taken several more years before the effects of chlorine would have been
large enough to produce a clearly detectable ozone hole without the enhancements due to thevolcanic aerosols. But as we contemplate the ways in which human-produced chlorine is
influenced by temperature and by volcanoes, it is helpful to underscore that there was no measurable ozone depletion after earlier eruptions such as that of Mt. Agung in 1966 or Mt. Fuego
in 1974. Cold temperatures, solid polar stratospheric clouds, and liquid volcanic particles are
all factors that modulate the ozone depletion, but the fundamental cause of the loss is the large
increase in ozone-destroying chlorine and bromine caused by human use of chlorofluorocarbons and, to a lesser extent, bromocarbons.

163

Figure 5. The top panel shows the evolution of the October monthly mean ozone at 75S. Total ozone measurements from Halley and from satellite data averages over the vortex are compared to model results run with and without considering observed aerosol surface area variations, updated from Portmann et al. (l996). The bottom panel
shows the factors which produced the model results: increasing active chlorine (Cly) due to CFC emissions andaerosol surface areas determined from satellite data. The eruptions of the volcanoes El Chichon in the early 1980s
and Pinatubo in the early 1990s are reflected in large enhancements in polar stratospheric cloud surface areas asshown.

164

Thus it has been my privilege to be involved in multiple phases of understanding ofozone loss chemistry in modeling and in observations. The picture has evolved from the gasphase alone to solids and liquids. Further, the understanding of liquid phase chemistry has led
to an evolution of thinking from extreme cold to less extreme, expanding both the processes
that must be considered and where they can occur in altitude and latitude. Today our ozone
layer is greatly depleted in the Antarctic, with some modulation from year to year depending
upon meteorological conditions and volcanic activity. Arctic ozone is also depleted, by asmuch as about 25% in cold years, and the ups and downs of meteorological variability are
extremely important in modulating the ozone loss from one year to another. Southern midlatitudes display more depletion than the north, and there are questions about the roles of interannual and interdecadal changes in meteorology for mid-latitude ozone changes, but there issignificant depletion of about 5-8% at mid-latitudes of both hemispheres. Thus, much of theworld’s population now lives under a reduced ozone shield and a greater level of ultraviolet
exposure than we did a generation ago. An important scientific question regarding mid-latitude ozone loss is the dilution of ozone-depleted air from higher latitudes, and the extent towhich surface chemistry occurring on cold air outside the polar regions may spread to lower
latitudes, enhancing the ozone loss.
4. Reflections on Ozone Depletion, Climate Change, and the Role of Science inEnvironmental Decision-Making
Policymakers met repeatedly to discuss evolving findings on ozone depletion during the late1980s and 1990s, and progressively developed global agreements to reduce and eventually tophase out the emissions of the responsible gases. Today the global annual emissions of CFCs
have dropped by more than 90% compared to their peak values, demonstrating the effectiveness of those policies. But the concentrations of the CFCs are dropping only very slowly,
because the cleansing of the atmosphere is limited by the lifetimes. For example, CFC-113
was used primarily as a solvent, and other chemicals and processes have now taken its placein those applications nearly worldwide, so that its global emissions are now close to zero. But
with an atmospheric lifetime of about 80 years, even the complete cessation of emissions canonly result in a slow decay at about 1% per year for this gas. Thus, the solvents used forexample during the boom in electronics in cleaning component chips in the 1980s, leading to
the modern lifestyle we enjoy today, will remain in our atmosphere and continue to depleteozone for many decades.
I would now like to briefly sketch some ideas about scientific parallels and differences
between ozone depletion and climate change, and I emphasize that these thoughts are purely
personal reflections.
Ozone depletion and climate change are different phenomena. Although the loss ofozone does have an influence on surface climate, perhaps even a very significant influence in
the Antarctic (see, e.g., Thompson and Solomon, 2002), it is not the primary cause of global
climate change. In fact, it leads to a cooling rather than a warming. Rather, global warming
is primarily driven by increases in carbon dioxide. But carbon dioxide is a gas with an average atmospheric lifetime of more than a century, just like some of the chlorofluorocarbons (see165

Table 1). Thus both of these environmental issues involve substances that last longer than ahuman lifetime, so both issues are a legacy that people are giving to their children and grandchildren. They challenge us to think beyond ourselves, to a longer-term view of the role ofeach generation, its footprint on the lives of the next, and even its footprint on civilization.
For both ozone depletion and climate change, well understood physical or
physical/chemical processes can be identified that imply that these gases surely do influence
the atmosphere – in the case of the CFCs, by increasing chlorine and depleting ozone; in thecase of carbon dioxide by altering the planetary energy budget, increasing the retention of radiant energy by the planet and hence leading to a warmer world.
For both ozone depletion and climate change, observations of the gases causing thechanges come from sites around the world, and in ice cores, and these clearly reveal the roleof man in driving today’s concentrations upward – in the case of carbon dioxide, to levels
higher than they have been in at least a half a million years.
In the case of ozone depletion, human-made chlorine undergoes chemistry, particularly
surface chemistry, that leads directly to large ozone losses. The processes involved are notgreatly dependent on how the atmosphere evolves (possible feedbacks) as depletion occurs.
But in the case of climate change, the scientific problem is challenging because the feedbacks
are known to be large, and may include stabilizing as well as destabilizing mechanisms.
Climate change increases surface temperatures and water vapor. The enhanced water vapor
can further enhance global warming, but just how much enhancement occurs depends sensitively on the amount and the vertical profile of the change. Further, climate change may leadto changes in cloudiness that reflect more radiation out to space (causing a stabilizing cooling
effect), or absorb more radiation (enhancing the warming). So the role of numerous large
feedbacks is critical for climate, making it a different scientific challenge than the large direct
impact of ozone depletion.
The strongly seasonal nature of the ozone depletion and its chemistry in Antarctica has
greatly facilitated its detection and attribution to CFCs. Because the Antarctic ozone holeopens up every year, and is accompanied by dramatic changes in many chemicals that we canobserve using multiple techniques (such as chlorine dioxide and nitrogen dioxide as discussed
in this paper), the relationship between chlorine chemistry and the ozone depletion can bedemonstrated in just a single season of observations – as it was in the 1980s. If we had notdone those measurements at that time, we could go to Antarctica now and in just one season
could show why the ozone there drops so quickly and dramatically. Global warming is a slow
and pervasive phenomenon, requiring careful measurements over many decades. It requires
consummate attention to long-term measurements rather than a short campaign. And it ismuch harder to measure all of the factors that are important (such as clouds, sea surface temperatures, water vapor, particulates, etc.) Thus the jigsaw puzzle of related observational evidence is far more difficult to assemble.
There is strong evidence that the global average temperature of the Earth increased during the 20th century, by about 0.6°C. Further, most of the globally averaged warming of thepast 50 years is attributable to human activities. Some regions have been subject to larger
trends, while others have experienced smaller changes or even localized cooling. Regional

166

variability in climate is a well-known phenomenon, and there is ample evidence for regionalscale fluctuations in the past. How are the observed regional changes linked to the global
mean change, and how much confidence can we place in projections for the future at bothglobal and smaller scales? This is a key scientific challenge, but I would suggest that it shows
why global warming is an even bigger societal challenge. That is because it represents yet
another way in which global warming challenges us to think beyond ourselves: to consider notjust what is occurring or may occur in our own backyards, but also those of our neighbors, aswell as those of people very far away, across huge gulfs of mountains, oceans, economies, andcultures.
Like ozone depletion, some key problems for climate change may relate to ice.
Formation and melting of ice relating to global warming is a phenomenon that merits carefulattention, because small changes in temperature can have important effects on phases of matter: solid versus liquid. While Antarctic sea ice trends have not yet been conclusively demonstrated, Arctic sea ice has declined in the past few decades, and dramatic changes have been
noted in some recent years. Snowpack and glaciers are also changing in many areas, with thepotential for large effects on water resources. Finally, the melting of the ice on the Greenlandor the West Antarctic ice sheets is a critical question for future climate change. The great ice
sheets have not always held as much water as they do today, and the consequences of that for
global sea level in the geologic past thousands of years ago were very large. Many scientists
are asking whether the Greenland ice sheet could melt due to global warming, with a related
rise in sea level of perhaps 3-6 meters. An interesting scientific question is whether it is the
Arctic or Antarctic polar ice sheet that is more likely to change in a warmer world. The possibility of changes in processes relating to ice at the two poles is a key vulnerability in the climate system – perhaps ironically, the same issue that has been a cornerstone of the ozone
problem and of my own scientific career.
But the possibility of stabilizing influences on ice and snow must also be carefully evaluated: could increased snowfall in a warmer wetter world with altered storm tracks compensate for rising Greenland temperatures, leaving the ice unchanged? Perhaps we will be lucky
and the competing influence of more melt will be exactly balanced, or even overbalanced insome places, by more snow. That implies that a critical issue in climate change is evaluationof the risk.
Science is an important input to societal choices about risk, but decisions about risk are
seldom made through science alone. They involve considerations ranging from science, tocultural values, to economics, to diplomacy and beyond. For both science and policy a key
question is how to use science objectively, so that future history books will document thathumankind dealt with climate change as wisely as I believe that it did with ozone depletion.
As I have emphasized in this lecture, that will challenge us to think very deeply, and very far
beyond ourselves: across generations and around this beautiful blue planet that is home to allof us.
References
Solomon, S., R.R. Garcia, F.S. Rowland, and D.J. Wuebbles, On the depletion of Antarctic ozone, Nature, 321,755-758, 1986.

167

Mount, G. H., R.W. Sanders, A.L. Schmeltekopf, and S. Solomon, Visible spectroscopy at McMurdo Station,
Antarctica, 1. Overview and daily variations of NO2 and O3, austral spring, 1986, J. Geophys. Res., 92, 83208328, 1987.
Solomon, S., G.H. Mount, R.W. Sanders and A.L. Schmeltekopf, Visible spectroscopy at McMurdo Station,
Antarctica, 2. Observation of OClO, J. Geophys. Res., 92, 8329-8338, 1987.
Solomon, S., G.H. Mount, R.W. Sanders, R.O. Jakoubek, and A.L. Schmeltekopf, Observation of the nighttime
abundance of OClO in the winter stratosphere above Thule, Greenland, Science, 242, 550-555, 1988.
Hofmann, D., and S. Solomon, Ozone destruction through heterogeneous chemistry following the eruption of El
Chichon, J. Geophys. Res., 94, 5029-5041, 1989.
Sanders, R. W., S. Solomon, J. P. Smith, L. Perliski, H. L. Miller, G. H. Mount, J. G. Keys, and A. L. Schmeltekopf,
Visible and near-ultraviolet spectroscopy at McMurdo Station, Antarctica, 9. Observations of OClO from
April-October, l99l, J. Geophys. Res., 98, 7219-7228, l993.
Solomon, S., R. W. Sanders, R. R. Garcia, and J. G. Keys, Increased chlorine dioxide over Antarctica caused byvolcanic aerosols from Mount Pinatubo, Nature, 363, 245-248, l993.
Hanson, D. H., A. R. Ravishankara, and S. Solomon, Heterogeneous reactions in sulfuric acid aerosols: a framework for model calculations, J. Geophys. Res., 99, 3615-3629, l994.
Portmann, R. W., S. Solomon, R. R. Garcia, L. W. Thomason, L. R. Poole, and M. P. McCormick, Role of aerosol
variations in anthropogenic ozone depletion in polar regions, J. Geophys. Res., 101, 22991-23006, l996.
Solomon, S., R. W. Portmann, R. R. Garcia, L. W. Thomason, L. R. Poole, and M. P. McCormick, The role ofaerosol variations in anthropogenic ozone depletion at northern mid-latitudes, J. Geophys. Res., 101, 6713-6727,
l996.
Solomon, S. R. W. Portmann, R. R. Garcia, W. Randel, F. Wu, R. Nagatani, J. Gleason, L. Thomason, L. R. Poole,and M. P. McCormick, Ozone depletion at mid-latitudes: Coupling of volcanic aerosols and temperature variability to anthropogenic chlorine, Geophys. Res. Lett., 25, 1871-1874, 1998.
Miller, H. L., R. W. Sanders, and S. Solomon, Observations and interpretation of column OClO seasonal cycles at
two polar sites, J. Geophys. Res., 104, 18769-18783, l999.
Solomon, S., Stratospheric ozone depletion: A review of concepts and history, Rev. Geophys., 37, 275-316, l999.
Thompson, D. W. J., and S. Solomon, Interpretation of recent southern hemisphere climate change, Science, 296,895-899, 2002.

168

Major Publications
Dr. Susan Solomon
Books:
Brasseur, G., and S. Solomon, Aeronomy of the Middle Atmosphere, Reidel Pub., Co., Dordrecht, 1984. (inEnglish, also translated into Russian and Chinese). Second edition, 1986. Third edition, 2005.
Solomon, S., The Coldest March, Yale University Press, New Haven and London, 2001. [selected for the prestigious '2001 Books of the Year' lists of the New York Times, the Economist (UK), and the Independent (UK)].
Finalist, Independent Publishers' Book Awards, 2001. Winner, Colorado Book Award, 2002. Louis Battan
Prize of the American Meteorological Society, 2003.
Journal Publications:Dr. Susan Solomon was named the third most highly cited geoscientist in the world during the decade of the 1990s
by Science Watch in December, 2001. Her publication record is as follows:
Fishman, J., S. Solomon, and P.J. Crutzen, Observational and theoretical evidence in support of a significant in situ
photochemical source of tropospheric ozone, Tellus, 31, 432, 1979.
Johnston, H.S. and S. Solomon, Thunderstorms as possible micrometeorological sink for stratospheric water, J.
Geophys. Res., 84, 3155, 1979.
Crutzen, P.J. and S. Solomon, Response of mesospheric ozone to particle precipitation, Planet. and Space Sci., 28,1147, 1980.
Solomon, S., H.S. Johnston, M. Kowalczyk, and I. Wilson, Instantaneous global ozone balance including observed
nitrogen dioxide, Pure App. Geophys., 118, 58, 1980.
Solomon, S. and P.J. Crutzen, Analysis of the August 1972 solar proton event including chlorine chemistry, J.
Geophys. Res., 86, 1140, 1980.
Rusch, D.W., J.C. Gerard, S. Solomon, P.J. Crutzen, and G.C. Reid, The effect of particle precipitation events on
the neutral and ion chemistry of the middle atmosphere - I. Odd nitrogen, Planet. and Space Sci., 29, 767, 1981.
Solomon, S., D.W. Rusch, J.C. Gerard, G.C. Reid, and P.J. Crutzen, The effect of particle precipitation on the neutral and ion chemistry of the middle atmosphere - II. Odd hydrogen, Planet. and Space Sci., 29, 885, 1981.
Solomon, S., P.J. Crutzen, and R.G. Roble, Photochemical coupling between the thermosphere and the lower
atmosphere I. Odd nitrogen from 50 to 120 km, J. Geophys. Res., 87, 7206, 1982.
Solomon, S., G.C. Reid, R.G. Roble, and P.J. Crutzen, Photochemical coupling between the thermosphere and thelower atmosphere II. D region ion chemistry and winter anomaly, J. Geophys. Res., 87, 7221, 1982.
Solomon, S., E.E. Ferguson, D.W. Fahey and P.J. Crutzen, On the chemistry of H2O, H2 and meteoritic ions in themesosphere and lower thermosphere, Planet. Space Sci., 30, 1117, 1982.
Garcia, R.R., and S. Solomon. A numerical model of the zonally averaged dynamical and chemical structure of the
middle atmosphere, J. Geophys. Res., 88, 1379, 1983.
Solomon, S., The possible effects of translationally excited nitrogen atoms on lower thermospheric odd nitrogen,
Planet. Space Sci., 31, 135, 1983.
Solomon, S., Minor constituents in the stratosphere and mesosphere, Rev. Geophys. Space Phys., 21, 276, 1983.
Solomon, S., G.C. Reid, D.W. Rusch, and R.J. Thomas, Mesospheric ozone depletion during the solar proton eventof July 13, 1982, Part II. Comparison between theory and measurements, Geophys. Res. Lett., 10, 257, 1983.
Solomon, S., D.W. Rusch, R.J. Thomas and R.S. Eckman, Comparison of mesospheric ozone abundances measured by the solar mesosphere explorer and model calculations, Geophys. Res. Lett., 10, 249, 1983.
Solomon, S., and R.R. Garcia, On the distribution of nitrogen dioxide in the high latitude stratosphere, J. Geophys
Res., 88, 5497, 1983.
Solomon, S., and R.R. Garcia, Simulation of NOx partitioning along isobaric parcel trajectories, J. Geophys. Res.,88, 5497, 1983.
Garcia, R.R., S. Solomon, R.G. Roble, and D.W. Rusch, A numerical model study of the response of the middle
atmosphere to changing solar activity, Planet. Space Sci., 32, 411, 1984.
Russell, J.M., S.Solomon, L.Gordley, E.Remsberg, and L.Callis, The variability of stratospheric and mesospheric
NO2 in the polar winter night observed by LIMS, J. Geophys. Res., 89, 7267, 1984.
Solomon, S., and R.R. Garcia, Transport of thermospheric NO to the upper stratosphere?, Planet. Space Sci., 32,169

399, 1984.
Solomon, S., and R.R. Garcia, On the distribution of long lived tracers and chlorine species in the middle atmosphere, J. Geophys. Res., 89, 11633, 1984.
Solomon, S., G.H. Mount, and J.M. Zawodny, Measurements of stratospheric NO2 from the solar mesosphere
explorer satellite II. General morphology of observed NO2 and derived N2O5, J. Geophys. Res., 89, 7317,
1984.
Thomas, R.J., C.Barth, and S.Solomon, Seasonal variations of ozone in the upper mesosphere and gravity waves,Geophys. Res. Lett., 11, 673, 1984.
Garcia, R.R., and S.Solomon, The effect of breaking gravity waves on the dynamics and chemical composition of
the mesosphere and lower thermosphere, J. Geophys. Res., 90, 3850, 1985.
Solomon, S., R.R. Garcia, J.J. Olivero, R.M. Bevilacqua, P.R. Schwartz, R.T. Clancy, and D.O. Muhleman,
Photochemistry and transport of carbon monoxide in the middle atmosphere, J. Atmos. Sci., 42, 1072, 1985.
Solomon, S., R.R. Garcia, and F. Stordal, Transport processes and ozone perturbations, J. Geophys. Res., 90,
12981-12989, 1985.
Austin, J., R.R. Garcia, J.M. Russell, S.Solomon, and A.F. Tuck, On the atmospheric photochemistry of nitric acid,
J. Geophys. Res., 91, 5477-5485, 1986.
Kiehl, J.T., and S.Solomon, On the radiative balance of stratosphere, J. Atmos. Sci., 43, 1525-1534, 1986.
Reid, G.C., and S. Solomon, On the existence of an extraterrestrial source of water vapor in the middle atmosphere,
Geophys. Res. Lett., 13, 1129-1132, 1986.
Solomon, S., J.M. Russell III, and L.L. Gordley, Observations of the diurnal variation of nitrogen dioxide in thestratosphere, J. Geophys. Res., 91, 5455-5464, 1986.
Solomon, S., R.R. Garcia, F.S. Rowland, and D.J. Wuebbles, On the depletion of Antarctic ozone, Nature, 321,755-758, 1986.
Solomon, S., J.T. Kiehl, R.R. Garcia, and W. Grose, Tracer transport by the diabatic circulation deduced from satellite observations, J. Atmos. Sci., 43, 1603-1617, 1986.
Solomon, S., J.T. Kiehl, B.J. Kerridge, E. E. Remsberg, and J.M. Russell, Evidence for non-local thermodynamic
equilibrium in the n3 mode of mesospheric ozone, J. Geophys. Res., 91, 9865-9876, 1986.
Bjarnason, G. G., S. Solomon, and R.R. Garcia, Tidal influences on vertical diffusion and diurnal variability ofozone in the mesosphere, J. Geophys. Res., 92, 5609-5620, 1987.
Garcia, R. R., S. Solomon, S.K. Avery and G.C. Reid, Transport of nitric oxide and the D-region winter anomaly,
J. Geophys. Res., 92, 977-994, 1987.
Garcia, R.R., and S. Solomon, A possible relationship between interannual variability in Antarctic ozone and thequasi-biennial oscillation, Geophys. Res. Lett., 14, 848-851, 1987.
LeTexier, H., S. Solomon, and R.R. Garcia, Seasonal variability of the OH Meinel bands, Planet. Space Sci., 35,
977-989 1987.
Roble, R.G., B.A. Emery, T.L. Killeen, G.C. Reid, S. Solomon, R.R. Garcia, D.S. Evans, P.B. Hays, G.R. Carrigan,
R.A. Heelis, W.B. Hanson, D.J.Winningham, N.W. Spencer, and L.H. Brace, Joule heating in the mesosphereand thermosphere during the July 13, 1982 solar proton event, J. Geophys. Res., 92, 6083-6090, 1987.
Solomon, S., A.L. Schmeltekopf, and R.W. Sanders, On the interpretation of zenith sky absorption measurements,
J. Geophys. Res., 92, 8311-8319, 1987.
Mount, G. H., R.W. Sanders, A.L. Schemltekopf, and S. Solomon, Visible spectroscopy at McMurdo Station,
Antarctica, 1. Overview and daily variations of NO2 and O3, austral spring, 1986, Geophys. Res., 92, 83208328, 1987.
Solomon, S., G.H. Mount, R.W. Sanders and A.L. Schemltekopf, Visible spectroscopy at McMurdo Station,
Antarctica, 2. Observation of OClO, J. Geophys. Res., 92, 8329-8338, 1987.
Sanders, R. W., S. Solomon, G.H. Mount, M.W. Bates and A.L. Schmeltekopf, Visible spectroscopy at McMurdo
Station Antarctica, 3. Observations of NO3, J. Geophys. Res., 92, 8339-8342, 1987.
Solomon, S., and R.R. Garcia, Current understanding of mesospheric transport processes, Phil. Trans. R. Soc.
Lond. A, 323, 655-666, 1987.
Spear, K.A., and S. Solomon, Mesospheric ionization and O2 (1Δg) depletion, Planet. Space Science., 35, 10571091, 1987.
Le Texier, H., S. Solomon, and R.R. Garcia, The role of molecular hydrogen and methane oxidation in the water
vapor budget of the stratosphere, Quart. J. Roy. Met. Soc., 114, 281-295, 1988.

170

Solomon, S., The mystery of the Antarctic ozone hole, Rev. Geophys, 26, 131-148, 1988.
Mount, G.H., S. Solomon, R.W. Sanders, R.O. Jakoubek, and A.L. Schmeltekopf,
Observations of stratospheric NO2 and O3 at Thule, Greenland, Science, 242, 555-558, 1988.
Solomon, S., G.H. Mount, R.W. Sanders, R.O. Jakoubek, and A.L. Schmeltekopf, Observation of the nighttime
abundance of OClO in the winter stratosphere above Thule, Greenland, Science, 242, 550-555, 1988.
Hofmann, D., and S. Solomon, Ozone depletion through heterogeneous chemistry following the eruption of the El
Chichon Volcano, J. Geophys. Res., 94, 5029-5041, 1989.
Le Texier, H., S. Solomon, R.J. Thomas and R.R. Garcia, OH (7-5) Meinel band day glow and night glow measured
by the SME limb scanning near infrared spectrometer: comparison of the observed seasonal variability with
two-dimensional model simulations, Ann. Geophysicae, 7, 365, 1989.
Sanders, R.W., S. Solomon, M.A. Carroll, and A.L. Schmeltekopf, Visible and near-ultraviolet spectroscopy at
McMurdo Station, Antarctica, 4. overview and daily measurements of NO2, O3 and OClO in 1989, J. Geophys.
Res., 94, 11381, 1989.
Solomon, S., R.W. Sanders, M.A. Carroll and A.L. Schmeltekopf, Visible and near-ultraviolet spectroscopy at
McMurdo Station, Antarctica, 5. Diurnal variations of OClO and BrO, J. Geophys. Res., 94, 11393, 1989.
Carroll, M.A., R.W. Sanders, S. Solomon, and A.L. Schmeltekopf, Visible and near-ultraviolet spectroscopy at
McMurdo Station, Antarctica, 6. Observations of BrO, J. Geophys. Res., 94, 16633, 1989.
Solomon, S., H.L. Miller, Jr., J.P. Smith, R.W. Sanders, G.H. Mount, A.L. Schmeltekopf, and J.F. Noxon,
Atmospheric NO3, 1. Measurement technique and the annual cycle at 40°N, J. Geophys. Res., 94, 1104111048, 1989.
Solomon, S., R. W. Sanders, G. H. Mount, M. A. Carroll, R. O. Jakoubek and A. L. Schmeltekopf, AtmosphericNO3, 2. Observations in polar regions, J. Geophys. Res., 94, 16423-16428, l989.
Perliski, L., S. Solomon and J. London, On the interpretation of seasonal variations in stratospheric ozone, Planet.
Space. Sci., 37, 1527, l989.
Vaida, V., S. Solomon, E. C. Richard, E. Ruehl, and A. Jefferson, Photoisomerisation of OClO: a polar ozone
depletion mechanism, Nature, 342, 405-408, l989.
Poole, L. R., S. Solomon, M. P. McCormick and M. C. Pitts, The interannual variability of polar stratosphericclouds and related parameters in Antarctica during September and October, Geophys. Res. Lett., 16, 11571160, l989.
Smith, J. P., and S. Solomon, Atmospheric NO3, 3. Sunrise disappearance and the stratospheric profile, J. Geophys.
Res., 95, 13819, l990.
Jones, R. L., D. S. McKenna, L. R. Poole and S. Solomon, On the influence of polar stratospheric clouds on chemical composition during the l988/9 Arctic winter, Geophys. Res. Lett., 17, 545, l990.
Jones, R. L., D. S. McKenna, L. R. Poole, and S. Solomon, Simulating the evolution of the chemical compositionof the l988/9 winter vortex, Geophys. Res. Lett., 17, 549, l990.
Poole, L. R., S. Solomon, B. W. Gandrud, K. A. Powell, J. Dye, R. L. Jones, and D. J. McKenna, The polar stratospheric cloud event of January 24, l989, 1., Microphysics, Geophys. Res. Lett., 17, 537, l990.
Jones, R. L., S. Solomon, D. S. McKenna, L. R. Poole, W. H. Brune, D. Toohey, J. G. Anderson and D. W. Fahey,
The polar stratospheric cloud event of January 24, l989, 2., Photochemistry, Geophys. Res. Lett., 17, 541,
l990.
McKenna, D. S., R. L. Jones, L. R. Poole, S. Solomon, D. W. Fahey, K. K. Kelly, M. T. Proffitt, W. H. Brune, M.
Loewenstein and K. R. Chan, Calculations of ozone destruction during the l988/9 Arctic winter, Geophys. Res.
Lett., 17, 553, l990.
Fahey, D. W., S. Solomon, S. R. Kawa, M. Loewenstein, J. R. Podolske, S. E. Strahan, and K. R. Chan, Reactive
nitrogen and nitrous oxide in the lower polar stratosphere: a case study in the coupling of photochemistry anddynamics, Nature, 345, 698, l990.
Solomon, S., Nitrogen chemistry in Antarctica: A brief review, in NATO Advanced Study Workshop on the Middle
Atmosphere of the Southern Hemisphere, A. O'Neill and C. Mechoso, eds., pp. 191-202, D. Reidel Pub. Co.,
l990.
Salby, M. L., P. Callaghan, S. Solomon, and R. R. Garcia, Chemical fluctuations associated with vertically propagating equatorial Kelvin waves, J. Geophys. Res., 95, 20491-20506, l990.
Solomon, S., R. W. Sanders, and H. L. Miller, Jr., Visible and near-ultraviolet spectroscopy at McMurdo Station,
Antarctica, 7. OClO diurnal photochemistry and implications for ozone destruction, J. Geophys. Res., 95,

171

13807, l990.
Solomon, S., Antarctic ozone: progress towards a quantitative understanding, Nature, 347, 347-354, l990.
Kawa, S. R., D. W. Fahey, S. Solomon, D. L. Anderson, W. H. Brune, M. H. Proffitt, D. W. Toohey, L. C.
Anderson, and K. R. Chan, Interpretation of aircraft measurements of NO, ClO, and O3 in the lower stratosphere, J. Geophys. Res., 95, 18597, l990.
Mlynczak, M. G. and S. Solomon, Middle atmosphere heating by exothermic chemical reactions involving oddhydrogen species, Geophys. Res. Lett., 18, 37, l991.
Mlynczak, M. G., and S. Solomon, On the efficiency of solar heating in the middle atmosphere, Geophys. Res.
Lett., 18, 1201, l99l.
Reid, G. C., S. Solomon, and R. R. Garcia, Response of the middle atmosphere to the solar proton events of AugustDecember, l989, Geophys. Res. Lett., 18, 1019, l99l.
McKenzie. R. L., P. V. Johnston, J. B. Kerr, C. T. McElroy, and S. Solomon, Altitude distributions of stratosphericconstituents from ground based measurements at twilight, J. Geophys. Res., 96, 15499, 199l.
Solomon, S., and J. G. Keys, Seasonal variations in Antarctic NOx chemistry, J. Geophys. Res., 97, 7971, l992.
Kawa, S. R., D. W. Fahey, L. E. Heidt, S. Solomon, D. E. Anderson, M. Loewenstein, M. H. Proffitt, J. J. Margitan,
and K. R. Chan, Photochemical partitioning of the reactive nitrogen and chlorine reservoirs in the high latitudestratosphere, J. Geophys. Res., 97, 7905, l992.
Solomon, S., M. J. Mills, L. E. Heidt, and A. F. Tuck, On the evaluation of ozone depletion potentials, J. Geophys.
Res., 97, 825, l992.
Proffitt, M. H., S. Solomon, and M. Loewenstein, Comparison of 2-D model simulations of ozone and nitrous oxide
at high latitudes with stratospheric measurements, J. Geophys. Res., 97, 939, l992.
Hofmann, D. J., S. J. Oltmans, J. M. Harris, S. Solomon, T. Deshler, and B. J. Johnson, Observation and possible
causes of new ozone depletion in Antarctica in l99l, Nature, 359, 283, l992.
Pollock, W. H., L. E. Heidt, R. E. Lueb, J. E. Vedder, M. J. Mills, and S. Solomon, On the age of stratospheric air
and ozone depletion potentials, J. Geophys. Res., 97, 12993, l992.
Solomon, S., and D. L. Albritton, A new analysis of time-dependent ozone depletion potentials, Nature, 357, 33,
l992.
Garcia, R. R., F. Stordal, S. Solomon, and J. T. Kiehl, A new numerical model of the middle atmosphere. 1.
Dynamics and transport of tropospheric source gases, J. Geophys. Res., 97, 12967-12991, l992.
Mellouki, A., R. K. Talukdar, A. M. Schmoltner, T. Gierczak, M. J. Mills, S. Solomon, and A. R. Ravishankara,
Atmospheric lifetimes and ozone depletion potentials of methyl bromide (CH3Br) and dibromomethane(CH2Br2), Geophys. Res. Lett., 19, 2059-2062, l992.
Perliski, L., and S. Solomon, Radiative effects of Mt. Pinatubo aerosols on ground-based visible spectroscopy
measurements of stratospheric NO2, Geophys. Res. Lett., 19, 1923-1926, l992.
Liu, X., R. D. Blatherwick, F. J. Murcray, G. Keys, and S. Solomon, Measurements and model calculations of HClcolumn density over McMurdo during the austral spring in l989, J. Geophys. Res., 97, 20795-20804, l992.
Ravishankara, A. R., S. Solomon, A. A. Turnipseed, and R. F. Warren, Atmospheric lifetimes of long-lived species,
Science, 259, 194-199, l993.
Solomon, S., J. P. Smith, R. W. Sanders, L. Perliski, H. L. Miller, G. H. Mount, J. G. Keys, and A. L. Schmeltekopf,
Visible and near-ultraviolet spectroscopy at McMurdo Station, Antarctica, 8. Observations of nighttime NO2
and NO3 from April-October, l99l, J. Geophys. Res., 98, 993-1000, l993.
Sanders, R. W., S. Solomon, J. P. Smith, L. Perliski, H. L. Miller, G. H. Mount, J. G. Keys, and A. L. Schmeltekopf,
Visible and near-ultraviolet spectroscopy at McMurdo Station, Antarctica, 9. Observations of OClO from
April-October, l99l, J. Geophys. Res., 98, 7219-7228, l993.
Perliski, L., and S. Solomon, On the evaluation of air mass factors for atmospheric near-ultraviolet and visible spectroscopy, J. Geophys. Res., 98, 10363-10374, l993.
Smith, J. P., S. Solomon, R. W. Sanders, H. L. Miller, L. M. Perliski, J. G. Keys, and A. L. Schmeltekopf,
Atmospheric NO3, 4. Vertical profiles at middle and polar latitudes at sunrise, J. Geophys. Res., 98, 8983-8989,
l993.
Mlynczak, M., and S. Solomon, A detailed evaluation of the heating efficiency in the middle atmosphere, J.
Geophys. Res., 98, 10517-10541, l993.
Mlynczak, M., S. Solomon, and D. Zaras, An updated model for O2 (1Δg) concentrations in the mesosphere andlower thermosphere and implications for remote sensing of ozone at 1.27 µm, J. Geophys. Res., 98, 18639-

172

18648, l993.
Mills, M. J., A. O. Langford, T. J. O'Leary, K. Arpag, H. L. Miller, M. H. Proffitt, R. W. Sanders, and S. Solomon,
On the relationship between stratospheric aerosols and nitrogen dioxide, Geophys. Res. Lett., 20, 1187-1190,
l993.
Solomon, S., R. W. Sanders, R. R. Garcia, and J. G. Keys, Enhanced chlorine dioxide and ozone depletion in
Antarctica due to volcanic aerosols, Nature, 363, 245-248, l993.
Burkholder, J. B., R. L. Mauldin III, R. J. Yokelson, S. Solomon, and A. R. Ravishankara, Kinetic, thermochemical, and spectroscopic study of Cl2O3, J. Phys. Chem., 97, 7597-7605, l993.
Burkholder, J. B., R. Talukdar, A. R. Ravishankara, and S. Solomon, Temperature dependence of the HNO3 UV
absorption cross sections, J. Geophys. Res., 98, 22937-22948, l993.
Schauffler, S. M., L. E. Heidt, W. H. Pollock, T. M. Gilpin, J. Vedder, S. Solomon, R. A. Lueb, and E. L. Atlas,
Measurements of halogenated organic compounds near the tropical tropopause, Geophys. Res. Lett., 20, 25672570, l993.
Webster, C. R., R. D. May, D. W. Toohey, L. M. Avallone, J. G. Anderson, and S. Solomon, In-situ measurementsof the ClO/HCl ratio: heterogeneous processing on sulfate aerosols and polar stratospheric clouds, Geophys.
Res. Lett. 20, 2523-2526, l993.
Hanson, D. H., A. R. Ravishankara, and S. Solomon, Heterogeneous reactions in sulfuric acid aerosols: a framework for model calculations, J. Geophys. Res., 99, 3615-3629, l994.
Kondo, Y., W. A. Matthews, S. Solomon, M. Koike, M. Hayashi, K. Yamazaki, H. Nakajima, and K. Tsukui,
Ground-based measurements of column amounts of NO2 and O3 over Syowa Station, Antarctica, J. Geophys.
Res., 99, 14535-14548, l994.
Solomon, S., R. W. Sanders, R. O. Jakoubek, K. Arpag, S. L. Stephens, J. G. Keys, and R. R. Garcia, Visible andnear-ultraviolet spectroscopy at McMurdo Station, Antarctica 10. Reductions of stratospheric NO2 due to
Pinatubo aerosols, J. Geophys. Res., 99, 3509-3516, l994.
Arpag, K. A., P. V. Johnston, H. L. Miller, R. W. Sanders, and S. Solomon, Observations of the stratospheric BrO
column over Colorado, 40°N, J. Geophys. Res., 99, 8175-8181, l994.
Garcia, R. R., and S. Solomon, A new numerical model of the middle atmosphere, 2, Ozone and related species, J.
Geophys. Res., 99, 12937-12951, l994.
Ravishankara, A. R., A. A. Turnipseed, N. R. Jensen, S. Barone, M. Mills, C. J. Howard, and S. Solomon, Do
hydrofluorocarbons destroy stratospheric ozone, Science, 263, 71-75, l994.
Solomon, S., R. R. Garcia, and A. R. Ravishankara, On the role of iodine in ozone depletion, J. Geophys. Res., 99,
20491-20499, l994.
Solomon, S., J. Burkholder, A. R. Ravishankara, and R. R. Garcia, Ozone depletion and greenhouse warming
potentials of CF3I, J. Geophys. Res., 99, 20929-20935, l994.
Daniel, J.S., S. Solomon, and D. L. Albritton, On the evaluation of halocarbon radiative forcing and global warming potentials, J. Geophys. Res., 100, 1271-1285, l995.
Woodbridge, E. L., J. W. Elkins, D. W. Fahey, L. E. Heidt, S. Solomon, T. J. Baring, T. M. Gilpin, W. H. Pollock,
S. M. Schauffler, E. L. Atlas, M. Loewenstein, J. R. Podolske, C. R. Webster, R. D. May, J. M. Gilligan, S. A.
Montzka, K. A. Boering, and R. J. Salawitch, Estimates of total organic and inorganic chlorine in the lower
stratosphere from in-situ and flask measurements during AASE II, J. Geophys. Res., 100, 3057-3064, l995.
Morris, R. A., T. M. Miller, A. A. Viggiano, J. F. Paulson, S. Solomon, and G. C. Reid, Effects of electron and ion
reactions on atmospheric lifetimes of fully fluorinated compounds, J. Geophys. Res., 100, 1287-1294, l995.
Burkholder, J. B., A. R. Ravishankara, and S. Solomon, UV/visible and IR absorption cross sections of BrONO2,
J. Geophys. Res., 100, 16793-16800, l995.
Portmann, R. W., G. E. Thomas, S. Solomon, and R. R. Garcia, The importance of dynamical feedbacks on doubled CO2-induced changes in the thermal structure of the mesosphere, Geophys. Res. Lett., 22, 1733-1736,
1995.
Solomon, S., and J. S. Daniel, Impact of the Montreal Protocol and its amendments on the rate of change of global
radiative forcing, Climatic Change, 32, 7-17, 1996.
Solomon, S., R. W. Portmann, R. R. Garcia, L. W. Thomason, L. R. Poole, and M. P. McCormick, The role ofaerosol variations in anthropogenic ozone depletion at northern mid-latitudes, J. Geophys. Res., 101, 67136727, l996.
Portmann, R. W., S. Solomon, R. R. Garcia, L. W. Thomason, L. R. Poole, and M. P. McCormick, Role of aerosol

173variations in anthropogenic ozone depletion in polar regions, J. Geophys. Res., 101, 22991-23006, l996.
Nevison, C. D., S. Solomon, and J. M. Russell, Nighttime formation of N2O5 inferred from Halogen Occultation
Experiment sunset/sunrise NOx ratios, J. Geophys. Res., 101, 6741-6748, l996.
Zander, R., S. Solomon, E. Mahieu, A. Goldman, C. P. Rinsland, M. R. Gunson, M. C. Abrams, A. Y. Chang, R.
J. Salawitch, H. A. Michelsen, M. J. Newchurch, and G. P. Stiller, Increase of stratospheric carbon tetrafluoride (CF4) based on ATMOS observations from space, Geophys. Res. Lett., 23, 2353-2356, l996.
Gierczak, T., R. K. Talukdar, J. B. Burkholder, R. W. Portmann, J. S. Daniel, S. Solomon, and A. R. Ravishankara,
Atmospheric fate and greenhouse warming potentials of HFC-236fa and HFC-236ea, J. Geophys. Res., 101,
12905-12911, l996.
Weaver, A., S. Solomon, R. W. Sanders, K. Arpag and H. L. Miller, Atmospheric NO3, 5, Off-axis measurements
at sunrise: estimates of tropospheric NO3 at 40°N, J. Geophys. Res., 101, 18605-18612, l996.
Daniel, J. S., S. M. Schauffler, W. H. Pollock, S. Solomon, A. Weaver, L. E. Heidt, R. R. Garcia, E. L. Atlas, andJ. F. Vedder, On the age of stratospheric air and inorganic chlorine and bromine release, J. Geophys. Res., 101,
16757-16770, l996.
Hauglustaine, D. A., B. A. Ridley, S. Solomon, P. G. Hess, and S. Madronich, HNO3/NOx ratio in the remote troposphere during MLOPEX 2: evidence for nitric acid reduction on carbonaceous aerosols, Geophys. Res. Lett.,
23, 2609-2612, l996.
Borrmann, S., S. Solomon, J. E. Dye, and B. Luo, The potential of cirrus clouds for heterogenous chlorine activation, Geophys. Res. Lett., 23, 2133-2136, l996.
Borrmann, S., S. Solomon, J. E. Dye, D. Baumgardner, K. K. Kelly, and K. R. Chan, Heterogeneous reactions on
stratospheric background aerosols, volcanic sulfuric acid droplets, and type 1 PSCs: The effects of temperature fluctuations and differences in particle phase, J. Geophys. Res., 102, 3639-3648, l997.
Portmann, R. W., S. Solomon, J. Fishman, J. R. Olson, J. T. Kiehl, and B. Briegleb, Radiative forcing of the Earth's
climate system due to tropical tropospheric ozone production, J. Geophys. Res., 102, 9409-9418, l997.
Nevison, C. D., S. Solomon, R. R. Garcia, D. W. Fahey, E. R. Keim, M. Loewenstein, J. R. Podolske, R. S. Gao,
R. C. Wamsley, S. G. Donnelly, and L. A. DelNegro, Influence of Antarctic denitrification on two-dimensionalmodel NOy/N2O correlations in the lower stratosphere, J. Geophys. Res., 102, 13183-13192, l997.
Solomon, S., S. Borrmann, R. R. Garcia, R. W. Portmann, L. W. Thomason, L. R. Poole, D. Winker, and M. P,
McCormick, Heterogeneous chlorine chemistry in the tropopause region, J. Geophys. Res., 102, 21411-21429,
l997.
Borrmann, S., S. Solomon, L. Avallone, D. Toohey, and D. Baumgardner, On the occurrence of ClO in cirrus
clouds and volcanic aerosol in the tropopause region, Geophys. Res. Lett., 24, 2011-2014, l997.
Gilles, M. K., A. A. Turnipseed, J. B. Burkholder, A. R. Ravishankara, and S. Solomon, Kinetics of the IO radical,
2, Reaction of IO with BrO, J. Phys. Chem., 101, 5526-5534, l997.
Nevison, C. D., S. Solomon, and R. R. Garcia, Model overestimates of NOy in the upper stratosphere, Geophys.
Res. Lett., 24, 803-806, 1997.
Miller, H. L., A. Weaver, R. W. Sanders, K. Arpag, and S. Solomon, Measurements of arctic sunrise surface ozone
depletion events at Kangerlussuaq, Greenland (67°N, 51°W), Tellus, 49B, 496-509, 1997.
Solomon, S., Chemistry of the atmosphere and ozone depletion, series of lectures published in The Stratosphere and
Its Role in the Climate System, G. Brasseur, ed., NATO/ASI Series, vol. I, 54, Springer-Verlag, Berlin, l997.
Pan, L., S. Solomon, W. Randel, J. F. Lamarque, P. Hess, J. Gille, E. W. Chiou, and M. P. McCormick,
Hemispheric asymmetries and seasonal variations of the lowermost stratospheric water vapor and ozone
derived from SAGE II data, J. Geophys. Res., 102, 28177-28184, l997.
Solomon, S., R. W. Portmann, R. W. Sanders, and J. S. Daniel, Absorption of solar radiation by water vapor, oxygen, and related collision pairs in the Earth's atmosphere, J. Geophys. Res., 103, 3847-3858, l998.
Solomon, S., M. A. Lemone, C. H. Moeng, and R. Roesch, Survey of Policies on 'Stopping the Tenure Clock' forchild-rearing in atmospheric science departments, Bull. Am. Met. Soc., 79, 91-92, l998.
Solomon, S. R. W. Portmann, R. R. Garcia, W. Randel, F. Wu, R. Nagatani, J. Gleason, L. Thomason, L. R. Poole,and M. P. McCormick, Ozone depletion at mid-latitudes: coupling of volcanic aerosols and temperature variability to anthropogenic chlorine, Geophys. Res. Lett., 25, 1871-1874, 1998.
Daniel, J. and S. Solomon, On the climate forcing of carbon monoxide, J. Geophys. Res., 103, 13249-13260, l998.
Rinsland, C. P., R. J. Salawitch, M. R. Gunson, S. Solomon, R. Zander, E. Mahieu, A. Goldman, M. J. Newchurch,
F. W. Irion, and A. Y. Chang, Polar stratospheric descent of NOy and CO and Arctic denitrification during win-174

ter l992-l993, J. Geophys. Res., 104, 1847-1861, l999.
Nevison, C. D., S. Solomon, and R. S. Gao, Buffering interactions in the modeled response of stratospheric O3 toincreased NOx and HOx, J. Geophys. Res., 104, 3741-3754, l999.
Solomon, S., R. W. Portmann, R. W. Sanders, J. S. Daniel, W. Madsen, B. Bartram, and E. G. Dutton, On the roleof nitrogen dioxide in the absorption of solar radiation, J. Geophys. Res., 104, 12047-12058, l999.
Mills, M. J., O. B. Toon, and S. Solomon, A 2D microphysical model of the polar stratospheric CN layer, Geophys.
Res. Lett., 26, 1133-1136, l999.
Dvortsov, V. L., M. A. Geller, S. Solomon, S. M. Schauffler, E. L. Atlas, and D. R. Blake, Rethinking reactive halogen budgets in the midlatitude lower stratosphere, Geophys. Res. Lett., 26, 1699-1702, l999.
Daniel, J. S., S. Solomon, R. W. Sanders, R. W. Portmann, D. C. Miller, and W. Madsen, Implications for the water
monomer and dimer solar absorption from observations at Boulder, J. Geophys. Res., 104, 16785-16791, l999.
Sanders, R. W., S. Solomon, K. Kreher, and P. V. Johnston, An intercomparison of NO2 and OClO measurements
at Arrival Heights, Antarctica, during Austral Spring 1996, J. Atm. Chem., 33, 283-298, 1999.
Solomon, S., Stratospheric ozone depletion: A review of concepts and history, Rev. Geophys., 37, 275-316, l999.
Miller, H. L., R. W. Sanders, and S. Solomon, Observations and interpretation of column OClO seasonal cycles at
two polar sites, J. Geophys. Res., 104, 18769-18783, l999.
Nevison, C. D., E. R. Keim, S. Solomon, D. W. Fahey, J. W. Elkins, M. Loewenstein, and J. R. Podolske,
Constraints on N2O sinks inferred from observed tracer correlations in the lower stratosphere, Global
Biogeochem. Cyc., 13, 737-742, l999.
Daniel, J. S., S. Solomon, R. W. Portmann, and R. R. Garcia, Stratospheric ozone destruction: The importance ofbromine relative to chlorine, J. Geophys. Res., 104, 23871-23880, l999.
Solomon, S., and C. R. Stearns, On the role of the weather in the deaths of R. F. Scott and his companions, Proc.
Nat. Acad. Sci., 96, 13012-13016, 1999.
Kaercher, B., and S. Solomon, On the composition and optical extinction of particles in the tropopause region, J.
Geophys. Res., 104, 27441-27459, 1999.
Kiehl, J. T., T. L. Schneider, R. W. Portmann, and S. Solomon, Climate forcing due to tropospheric and stratospheric ozone, J. Geophys. Res., 104, 31239-31254, 1999.
Anderson, J., J. M. Russell III, S. Solomon, and L. E. Deaver, Halogen Occultation Experiment confirmation ofstratospheric chlorine decreases in accordance with the Montreal Protocol, J. Geophys. Res., 105, 4483-4490,
2000.
Portmann, R. W., S. Solomon, R. W. Sanders, J. S. Daniel, and E. G. Dutton, Cloud modulation of zenith sky oxygen photon path lengths over Boulder, Colorado: Measurement versus model, J. Geophys. Res., 106, 11391155, 2001.
Dvortsov, V., and S. Solomon, Response of the stratospheric temperatures and ozone to past and future increases
in stratospheric humidity, J. Geophys. Res., 106, 7505-7514, 2001.
Thompson, D. W. J., and S. Solomon, Interpretation of recent southern hemisphere climate change, Science, 296,895-899, 2002.
Daniel, J. S., S. Solomon, R. W. Portmann, A. O. Langford, C. S. Eubank, E. G. Dutton, and W. Madsen, Cloudliquid water and ice measurements from spectrally resolved near-infrared observations: a new technique, J.
Geophys. Res., 107, 4599, 2002.
Takahashi, K., T. Nakayama, Y. Matsumi, S. Solomon, T. Gejo, E. Shigemasa, and T. J. Wallington, Atmospheric
lifetime of SF5CF3, accepted for publication in Geophys. Res. Lett., 29, 101029, 2002.
Melamed, M. L., S. Solomon, J. S. Daniel, A. O. Langford, R. W. Portmann, T. B. Ryerson, D. K. Nicks, Jr., and
S. A. McKeen, Inferring reactive nitrogen emissions from point sources using visible spectroscopy measurements from aircraft, J. Env. Monit., 5. 20-34, 2003.
Zamora, R. J., S. Solomon, E. G. Dutton, J. W. Bao, M. Trainer, R. W. Portmann, A. B. White, and D. W. Nelson,
Comparing MM5 radiative fluxes with observations gathered during the 1995 and 1999 Nashville Southern
Oxidant Studies, J. Geophys. Res., 108, 4050, 2003.
Sierk, B., S. Solomon, J. S. Daniel, R. W. Portmann, S. I. Gutman, A. O. Langford, C. S. Eubank, K. H. Holub,
Field test of spectral line intensity parameters for tropospheric water vapor, J. Geophys. Res., 108, 4351, 2003.
Forster, P., and S. Solomon, Observations of a weekend effect in diurnal temperature range, Proc. Nat. Acad. Sci.,
100, 11225-11230, 2003.
Daniel, J. S., S. Solomon, H. L. Miller, A. O. Langford, R. W. Portmann, and C. S. Eubank, Retrieving cloud infor-

175

mation from passive measurements of solar radiation absorbed by molecular oxygen and O2-O2, J. Geophys.
Res., 108, 4515, 2003.
Hawes, A. K., S. Solomon, R. W. Portmann, J. S. Daniel, A. O. Langford, H. L. Miller, C. S. Eubank, P. Goldan,
C. Wiedinmyer, E. Atlas, A. Hanel, and A. Wisthaler, Airborne observations of vegetation and implications forbiogenic emission characterization, J. Env. Monit., 5, 977-983, 2003.
Solomon, S., The hole truth: What's news (and what's not) about the ozone hole, Nature, 427, 289-291, 2004.
Sierk, B., S. Solomon, J. S. Daniel, R. W. Portmann, S.I. Gutman, A. O. Langford, C. S. Eubank, E. G. Dutton, K.
H. Holub, Field measurements of water vapor continuum absorption in the visible and near-infrared, J.
Geophys. Res., 109, D08307, 2004.
Daniel, J. S., S. Solomon, H. G. Kjaergaard, and D. P. Schofield, Atmospheric water vapor complexes and the continuum, Geophys. Res. Lett., 31, L06118,doi: 10.1029/2003 GL018914, 2004.
Langford, A. O., R. W. Portmann, J. S. Daniel, H. L. Miller, and S. Solomon, Spectroscopic measurement of NO2
in a Colorado thunderstorm: Determination of the mean production by cloud-to-ground lightning flashes, J.
Geophys. Res., 109, D11304, 2004.
Solomon, S., and J. S. Daniel, Lewis and Clark: Pioneering Meteorological Observers in the American West, Bull.,Am. Met. Soc., DOI:10.1175/BAMS-85-9-1273-1288, September, 2004.
Thompson, D. W., M. P. Baldwin, and S. Solomon, Stratospheric precursors of tropospheric climate anomalies in
the Southern Hemisphere: 1979-2002, J. Atmos. Sci., 62, 708-715, 2005.
Langford, A. O., R.W. Portmann, J.S. Daniel, H. L. Miller, C.S. Eubank, and S. Solomon, Retrieval of ice crystal
effective diameters from ground-based near-infrared spectra of optically thin cirrus, J. Geophys. Res, 110,
D22201, doi:10.1029/2005JD005761, 2005.
P. Friedlingstein and S. Solomon, Contributions of past and present human generations to committed warming
caused by carbon dioxide, Proc. Nat. Acad. Sci., 102, 10832–10836, 2005.
Thompson, D. W. J., and S. Solomon, Recent Stratospheric Climate Trends as Evidenced in Radiosonde Data:
Global Structure and Tropospheric Linkages, J. Clim., 18, 4785-4795, 2005.
Solomon, S., R. W. Portmann, T. Sasaki, D. J. Hofmann, and D. W. J. Thompson, Four decades of ozonesondemeasurements over Antarctica, J. Geophys. Res., 110, D21311, doi:10.1029/2005JD005917, 2005.
S. Solomon, D. W. J. Thompson, R. W. Portmann, S. J. Oltmans, and A. M. Thompson, On the distribution andvariability of ozone in the tropical upper troposphere: Implications for tropical deep convection and chemicaldynamical coupling, Geophys. Res. Lett., 32, L23813, doi:10.1029/2005GL024323, 2005.
Sun, Y., S. Solomon, A. Dai, and R. W. Portmann, How often does it rain?, J. Clim., 19, 916-934, 2006.

176