Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts - Hardcover

Hardcover

ISBN 10: 0471214892 ISBN 13: 9780471214892

Publisher: Wiley-Interscience, 2003

Synopsis

The Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts is the first of two stand-alone volumes that will be landmarks in the meteorological literature for many years to come. Each volume encompasses both fundamental topics and critical issues that have recently surfaced in studies of the hydrosphere and atmosphere. Renowned experts have contributed to every part of this handbook. Each overview chapter is followed by topic-specific chapters written by specialists who present comprehensive discussions at a greater level of detail and complexity.

The Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts covers topics that are essential for grasping the scientific bases of major issues such as global climate warming, the ozone hole, acid rain, floods, droughts, and other natural disasters. Cross-references between chapters allow readers to easily pursue a specific interest beyond a particular subtopic or individual chapter.

Other topics include:

• Aerosols and smog
• Cloud chemistry
• Greenhouse gases
• Remote sensing techniques in hydrology
• Hydrologic forecasting and simulation
• Tropical deforestation effects on the climate system
• Societal impacts of the El Niño phenomenon

The Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts will be an essential addition to the libraries of professionals and academics in the environmental sciences, and a valuable source book for university and technical libraries throughout the world.

About this title

About the Author

THOMAS D. POTTER, PhD, is Professor of Meteorology at the University of Utah, Salt Lake City, and Director of NOAA Cooperative Institute for Regional Prediction.

BRADLEY R. COLMAN, ScD, is Science Operations Officer for the National Weather Association in Seattle, Washington, and holds affiliate faculty positions with the University of Washington and the University of Idaho.
Both are Fellows of the American Meteorology Society.

From the Back Cover

A comprehensive survey of fundamental principles and the latest research on atmospheric, climatic, and hydrologic sciences

The Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts is the first of two stand-alone volumes that will be landmarks in the meteorological literature for many years to come. Each volume encompasses both fundamental topics and critical issues that have recently surfaced in studies of the hydrosphere and atmosphere. Renowned experts have contributed to every part of this handbook. Each overview chapter is followed by topic-specific chapters written by specialists who present comprehensive discussions at a greater level of detail and complexity.

The Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts covers topics that are essential for grasping the scientific bases of major issues such as global climate warming, the ozone hole, acid rain, floods, droughts, and other natural disasters. Cross-references between chapters allow readers to easily pursue a specific interest beyond a particular subtopic or individual chapter.

Other topics include:

• Aerosols and smog
• Cloud chemistry
• Greenhouse gases
• Remote sensing techniques in hydrology
• Hydrologic forecasting and simulation
• Tropical deforestation effects on the climate system
• Societal impacts of the El Niño phenomenon

The Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts will be an essential addition to the libraries of professionals and academics in the environmental sciences, and a valuable source book for university and technical libraries throughout the world.

The Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts is the first of two stand-alone volumes that will be landmarks in the meteorological literature for many years to come. Each volume encompasses both fundamental topics and critical issues that have recently surfaced in studies of the hydrosphere and atmosphere. Renowned experts have contributed to every part of this handbook. Each overview chapter is followed by topic-specific chapters written by specialists who present comprehensive discussions at a greater level of detail and complexity.

The Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts covers topics that are essential for grasping the scientific bases of major issues such as global climate warming, the ozone hole, acid rain, floods, droughts, and other natural disasters. Cross-references between chapters allow readers to easily pursue a specific interest beyond a particular subtopic or individual chapter.

Other topics include:

• Aerosols and smog
• Cloud chemistry
• Greenhouse gases
• Remote sensing techniques in hydrology
• Hydrologic forecasting and simulation
• Tropical deforestation effects on the climate system
• Societal impacts of the El Niño phenomenon

The Handbook of Weather, Climate, and Water: Atmospheric Chemistry, Hydrology, and Societal Impacts will be an essential addition to the libraries of professionals and academics in the environmental sciences, and a valuable source book for university and technical libraries throughout the world.

Excerpt. © Reprinted by permission. All rights reserved.

Handbook of Weather, Climate, and Water

Atmospheric Chemistry, Hydrology, and Societal Impacts

John Wiley & Sons

Copyright © 2003 John Wiley & Sons, Inc.
All right reserved.
ISBN: 978-0-471-21489-2

Chapter One

OVERVIEW: ATMOSPHERIC CHEMISTRY

JACK FISHMAN

The study of atmospheric chemistry focuses on how chemical constituents cycle through the atmosphere. Excluding water vapor (which can account for as much as 2 to 3% of the volume of the atmosphere under extremely moist conditions), more than 99.9% of the remaining dry atmosphere is comprised of nitrogen (78.1%), oxygen, (20.9%), and argon (0.93%). Unlike the study of conventional meteorology, where the atmosphere is generally treated as a bulk medium, atmospheric chemistry focuses on each individual constituent (commonly referred to as trace gases) and the chemical reactions that take place among them.

When discussing atmospheric chemistry, it is perhaps most convenient to separate the discussion into two distinct chemical regimes: the stratosphere and the troposphere. In the stratosphere, the most important trace gas is ozone, [O.sub.3], whereas in the troposphere, it can be argued that one of the most important trace gases is carbon dioxide, C[O.sub.2]. Both of these trace gases are intimately tied to the issue of global change as measurements over the past several decades confirm that stratospheric ozone is decreasing and that carbon dioxide is increasing. Ozone in the stratosphere is vital for shielding the biosphere from harmful ultraviolet radiation; a decrease in the amount of ozone in the stratosphere will result in damage to biota at the ground. On the other hand, carbon dioxide is an important trace gas (second in importance to water vapor) that keeps infrared radiation within the lower atmosphere, and it is generally agreed that an increase in C[O.sub.2] may have important climatic implications and lead to global warming.

The source of energy that drives the chemical processes in the atmosphere is the same source that drives Earth's weather engine, namely the sun. Furthermore, the high-energy ultraviolet radiation emitted by the sun initiates a series of reactions in the upper atmosphere as these high-energy photons break the stable molecules, [N.sub.2] and [O.sub.2], apart into their atomic components. This high energy not only is capable of breaking these very strong molecular bonds apart, but it is also capable of stripping away electrons creating a source of ions in the atmosphere above ~50 km. This region of the atmosphere is called the ionosphere, and its chemistry will not be discussed in this section. For more information about the chemistry of the ionosphere, mesosphere, and thermosphere, see Brasseur and Solomon's (1986) Aeronomy of the Middle Atmosphere, Chapter 6 and various sections in Chapter 5. These ions and atoms can feed some of the chemical cycles that take place in the stratosphere, such as supplying reactive nitrogen species (e.g., see Fig. 1).

From an atmospheric chemistry point of view, important cycles take place in both the stratosphere and the troposphere; this section will concentrate on the chemistry taking place in these regions of the atmosphere. To a certain extent, the chemistry of the stratosphere is somewhat less complex than the chemistry in the troposphere because only large-scale meteorological processes are present at these high altitudes; smaller scale processes such as precipitation can be generally neglected. Also important is the fact that the sources of trace species in the stratosphere are not determined from small-scale sources and can thus can be quantified using a simplified methodology.

In the stratosphere, observing and gaining an understanding of how the distribution of ozone evolved was the primary research emphasis from the 1930s through the 1960s. Understanding how its abundance and distribution has been perturbed by anthropogenic inputs has been the focus of intense research efforts since the 1970s.

1 STRATOSPHERIC CHEMISTRY: UNDERSTANDING THE OZONE LAYER

Ozone was discovered in 1839 by the German scientist Christian Frederich Schonbein at the University of Basil in Switzerland. Because of its pungent odor, its name was taken from the Greek word ozein, meaning "odor." Schnbein's research, subsequent to his discovery, focused on verifying his hypothesis that ozone was a natural trace constituent of the atmosphere. As a result of interest in the late nineteenth century, there are a surprisingly large number of ambient measurements during that time.

The primary study of ozone focused on the chemistry of the stratosphere when it was hypothesized and then verified that most of Earth's ozone was located at an altitude of 20 to 50 km (also called the ozonosphere) high above Earth's surface. The British physicist Sir Sidney Chapman put forth the premise that sufficiently intense ultraviolet radiation [at wavelengths ([lambda]); [lambda] < 242 nm) breaks apart molecular oxygen into two oxygen atoms. This reaction is commonly written:

[O.sub.2] + hv [right arrow] O + O [lambda] < 242 nm (1)

where hv is the standard notation for a photon.

As the air becomes denser at lower altitudes in the stratosphere, most of this high-energy radiation is absorbed, and the oxygen molecules can no longer be broken apart. At these altitudes, the oxygen atoms will efficiently combine with the oxygen molecules and the formation of ozone occurs through the reaction:

O + [O.sub.2] + M [right arrow] [O.sub.3] + M (2)

where M is a nonreactive third body that absorbs any excess collisional energy that may be present. Thus, there is a preferred region in the atmosphere where sufficient ultraviolet energy is concurrently present with the proper amount of molecular density to create ozone, and the altitude region at which these processes are most prevalent is commonly referred to as the ozone layer.

Ozone can also be photolyzed in the atmosphere by weaker ultraviolet radiation ([lambda] < 320 nm) to give back molecular and atomic oxygen:

[O.sub.3] + hv [right arrow] [O.sub.2] + O([sup.1]D [lambda] < 320 nm (3)

and also by visible radiation ([lambda] < 600 nm) to yield atomic oxygen in its ground state, O3P+, rather than the more energetic O([sup.1]D) state; furthermore ozone can react with atomic oxygen (in either its ground or excited state) to give two molecules of oxygen:

[O.sub.3] + O [right arrow] 2[O.sub.2] (4)

To complete the possible reactions in a "pure oxygen" atmosphere, two atoms of oxygen can combine in a three-body reaction to give molecular oxygen back to the system:

O + O + M [right arrow] [O.sub.2] + M (5)

The set of five reactions involving only the various states of oxygen in the stratosphere are commonly referred to as "Chapman chemistry" and did a remarkable job of describing qualitatively why the ozone layer existed where it did. The speeds at which the five reactions took place in the atmosphere were measured independently in the laboratory and are called reaction rate constants (denoted [k.sub.4] for reaction 4, [k.sub.5] for reaction 5, etc.). Reaction rate constants are often temperature and pressure dependent. The rates of photolysis are noted by the letter j (e.g., [j.sub.3] for photolytic reaction 3, etc.) and are primarily dependent on the cross section of the individual molecule as a function of wavelength (those that have weaker bonds and can be broken apart more easily have larger cross sections) and the number of incident photons at those wavelengths (commonly called the photon flux).

As the field of chemistry progressed, other reactions were measured in the laboratory that were also believed to occur in the atmosphere with sufficient speed that they were eventually hypothesized to take an active role in the destruction and formation of ozone. These reactions dealt with derivatives of various forms of hydrogen in the stratosphere. The chemistry of the stratosphere was modified accordingly to account for this new "wet photochemistry," which involved reactions being measured in the laboratory, was in the 1950s and 1960s. The rationale behind this new chemistry was that atomic oxygen, O([sup.1]D), could react with water vapor to form the hydroxyl radical, OH:

[H.sub.2]O + O([sup.1]D) [right arrow] 2OH (6)

Another important source of reactive hydrogen in the stratosphere is degradation of methane C[H.sub.4], by O([sup.1]D). Regardless of the initial source of the OH radical, it could then react with ozone to form another radical, H[O.sub.2], the hydroperoxy radical, which can lead to a catalytic cycle that becomes an efficient mechanism by which ozone can be removed from the atmosphere:

OH + [O.sub.3] [right arrow] H[O.sub.2] + [O.sub.2] (7) H[O.sub.2] + [O.sub.3] [right arrow] OH + 2[O.sub.2] (8) 2[O.sub.3] [right arrow] 3[O.sub.2] (net cycle)

The above reactions helped to explain some of the observed differences between the measurements that were routinely made in the 1950s and 1960s and the calculated distribution of ozone determined from an oxygen-only atmosphere.

The next major modification to atmospheric chemistry came about from the inclusion of nitrogen chemistry into the reaction scheme of the stratosphere. Nitrous oxide, [N.sub.2]O, was known to be a natural trace gas in the troposphere which did not have any identifiable removable mechanisms in lower atmosphere. Consequently, it could drift to the stratosphere where it was eventually attacked by the O([sup.1]D) atom to form nitric oxide, NO:

[N.sub.2]O + O([sup.1]D) [right arrow] 2NO (9)

With the presence of NO in the stratosphere, another catalytic cycle of ozone destruction could occur through the following reaction sequence:

NO + [O.sub.3] [right arrow] N[O.sub.2] + [O.sub.2] (10) followed by N[O.sub.2] + O [right arrow] NO + [O.sub.2] (11) Net cycle [O.sub.3] + O [right arrow] 2[O.sub.2]

The importance of reactive nitrogen chemistry in the stratosphere was independently brought to light circa 1970 by Paul Crutzen, a recent Ph.D. in meteorology at the time from the University of Stockholm, and Harold Johnston, a chemistry professor at the University of California.

These catalytic ozone destruction cycles involving nitrogen and hydrogen species were the impetus behind the Climatic Impact Assessment Program (CIAP) of the 1970s, which became the rationale for determining the potential damage to the ozone layer that might result from flying a fleet of supersonic transport (SST) planes in the lower stratosphere. These planes would emit NO and [H.sub.2]O directly into the stratosphere, and a confederation of U.S. federal agencies was charged with the task of determining how the ozone layer would be harmed by such a fleet. Although economic considerations eventually lay behind the decision for the United States not to pursue the development of a commercial fleet of SSTs, the environmental debate that developed during the early 1970s also contributed to the decision not to pursue the building of this new type of airplane.

But the environmental concern became even more of a reason to spend an increasing amount of money on stratospheric chemistry when Ralph Cicerone and Richard Stolarski, both at the University of Michigan in the early 1970s, introduced the possibility that chlorine chemistry might also provide another important means by which stratospheric ozone might be destroyed:

Cl + [O.sub.3] [right arrow] ClO + [O.sub.2] (12) followed by ClO + O [right arrow] Cl + [O.sub.2] (13) Net cycle: [O.sub.3] + O [right arrow] 2[O.sub.2]

Shortly after the chlorine cycle was identified as a potential mechanism for stratospheric ozone destruction, Mario Molina and F. Sherwood Rowland, both chemists at the University of California at Irvine, proposed that a group of anthropogenic chlorine-containing compounds could provide the source of significant amounts of chlorine in the stratosphere (Molina and Rowland, 1974). These compounds, known as chlorofluoro-carbons (CF[Cl.sub.3] and C[F.sub.2][Cl.sub.2]) were used primarily in air-conditioning systems and as propellants for aerosol spray cans that proliferated the use of these compounds in the 1960s. These substances had no known removal mechanism in the troposphere, and Molina and Rowland hypothesized that their only eventual sink would be drifting to the upper stratosphere where they would be destroyed by high-energy ultraviolet radiation resulting in the release of their reactive chlorine atoms into the chemistry of the stratosphere. Figure 1 shows the chemical reactions within each reactive family [e.g., the reactive nitrogen family (NX) the reactive hydrogen family (HX), etc.] and also how each of these individual chemical cycles would influence stratospheric ozone chemistry. The circled trace gas in each box in Figure 1 is the longest-lived species for that particular reactive group. Chlorine nitrate (ClON[O.sub.2]) and nitric acid (HN[O.sub.3]) are long-lived trace gases that serve as reservoirs of more than one reactive family.

As predicted, the buildup in chlorine led to a "thinning" of the ozone layer. Not predicted by the atmospheric chemists, however, was that the depletion of ozone intensified in the Antarctic stratosphere because of the unique meteorological conditions there. Stratospheric dynamics are such that an enhanced circulation develops during austral winter, which severely inhibits meridional heat exchange (unlike the Northern Hemisphere, where the position of major mountain ranges closer to the pole results in a more favorable situation for heat from middle and low latitudes to be transported poleward). Thus, temperatures in the Antarctic lower stratosphere reach temperatures that are cold enough to allow for the formation of polar stratospheric clouds (PSCs) that provide ice surfaces that greatly perturb stratospheric chemistry by turning the long-lived (and relatively nonreactive) chlorine-containing compounds (chlorine nitrate, ClON[O.sub.2], and hydrochloric acid, HCl) into chlorine atoms, thereby greatly enhancing the destructive power of the reactive chlorine. Some of the main reactions that are influenced by PSCs are also shown in Figure 1 within the ClX box in the upper left of the figure. The net result has been the formation of the ozone hole whereby more than two-thirds of the normal amount of stratospheric ozone can be destroyed within a period few weeks as the austral winter ends (see Chapter 21, "Stratospheric Ozone Observations"). This phenomenon was first identified from ozonesonde measurements made by Joe Farman of the British Antarctic Survey in the early 1980s (Farman et al. 1985). By the early 1990s, more than 80% of the chlorine in the atmosphere was determined to be of anthropogenic origin (see Figure 2).

The environmental problem of stratospheric ozone depletion was successfully addressed by an international treaty in 1987 referred to as the Montreal Protocol, whereby a plan was set forth to phase out and eventually eliminate the manufacture and use of primary ozone-depleting chlorinated compounds (see Albritton et al., 1999). Figure 3 shows how the amount of man-made chlorine has decreased as a result of the effort to minimize the destruction of the ozone layer. As the amount of chlorine goes down in the stratosphere, model predictions suggest that the ozone hole should return to its pre-1980s level by the second or third decade of the new millennium. As a result of their important work on understanding the ozone layer and the chemical processes that drive the formation and destruction of ozone in both the stratosphere and the troposphere, Paul Crutzen, Mario Molina, and F. Sherwood Rowland were awarded the Nobel Prize for chemistry in 1995, the first time that atmospheric chemists received this coveted award. Whereas Rowland and Molina were both trained as chemists, Crutzen is the first meteorologist to receive the Nobel Prize.

Despite the complexity of Figure 1, it has been simplified by excluding the chemistry of two other halogen compounds: bromine and iodine. Reactive family chemistry of these halogens is similar to that shown for the reactive chlorine family. Anthropogenic bromine compounds (called halons) are used as fumigants in agriculture and as a fire retardant on clothing. The most abundant iodine compound is methyl iodide, C[H.sub.3]I, and has been observed in the atmosphere as a biomass burning product.

(Continues...)

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Edition details

• Publisher: Wiley-Interscience
• Publication date: 2003
• ISBN 10: 0471214892
• ISBN 13: 9780471214892
• Binding: Hardcover
• Language: English
• Edition number: 1
• Number of pages: 1020
• Editor: Potter Thomas D., Colman Bradley R.