# Introduction to Atmospheric Chemistry

DANIEL J. JACOB
Copyright Date: 1999
Pages: 264
https://www.jstor.org/stable/j.ctt7t8hg

## Table of Contents

1. Front Matter
(pp. i-iv)
2. Table of Contents
(pp. v-x)
3. Preface
(pp. xi-2)
4. 1 Measures of Atmospheric Composition
(pp. 3-13)

The objective of atmospheric chemistry is to understand the factors that control the concentrations of chemical species in the atmosphere. In this book we will use three principal measures of atmospheric composition:mixing ratio,number density, andpartial pressure. As we will see, each measure has its own applications.

Themixing ratio CXof a gasX(equivalently called themole fraction) is defined as the number of moles ofXper mole of air. It is given in units of mol/mol (abbreviation for moles per mole), or equivalently in units of v/v (volume of gas per volume of air)...

5. 2 Atmospheric Pressure
(pp. 14-23)

Theatmospheric pressureis the weight exerted by the overhead atmosphere on a unit area of surface. It can be measured with a mercury barometer, consisting of a long glass tube full of mercury inverted over a pool of mercury (figure 2-1).

When the tube is inverted over the pool, mercury flows out of the tube, creating a vacuum in the head space, and stabilizes at an equilibrium heighthover the surface of the pool. This equilibrium requires that the pressure exerted on the mercury at two points on the horizontal surface of the pool,A(inside the tube)...

6. 3 Simple Models
(pp. 24-41)

The concentrations of chemical species in the atmosphere are controlled by four types of processes:

Emissions. Chemical species are emitted to the atmosphere by a variety of sources. Some of these sources, such as fossil fuel combustion, originate from human activity and are calledanthropogenic. Others, such as photosynthesis of oxygen, originate from natural functions of biological organisms and are calledbiogenic. Still others, such as volcanoes, originate from nonbiogenic natural processes.

Chemistry. Reactions in the atmosphere can lead to the formation and removal of species.

Transport. Winds transport atmospheric species away from their point of origin.

Deposition. All material...

7. 4 Atmospheric Transport
(pp. 42-78)

We saw in chapter 3 that air motions play a key role in determining the distributions of chemical species in the atmosphere. These motions are determined by three principal forces: gravity, pressure-gradient, and Coriolis. We previously saw in chapter 2 that the vertical distribution of mass in the atmosphere is determined by a balance between gravity and the pressure-gradient force; when these forces are out of balancebuoyant motionsresult, which will be discussed in section 4.3. In the horizontal direction, where gravity does not operate, the equilibrium of forces usually involves a balance between the pressure-gradient force and the...

8. 5 The Continuity Equation
(pp. 79-86)

A central goal of atmospheric chemistry is to understand quantitatively how the concentrations of species depend on the controlling processes: emissions, transport, chemistry, and deposition. This dependence is expressed mathematically by thecontinuity equation, which provides the foundation for all atmospheric chemistry research models. In the present chapter we derive the continuity equation in itsEulerianform (fixed coordinate system) and in itsLagrangianform (moving coordinate system). We also describe the methods and approximations used to solve the continuity equation in atmospheric chemistry models. As we will see, the simple models presented in chapter 3 represent in fact drastic...

9. 6 Geochemical Cycles
(pp. 87-114)

So far we have viewed the concentrations of species in the atmosphere as controlled by emissions, transport, chemistry, and deposition. From an Earth system perspective, however, the composition of the atmosphere is ultimately controlled by the exchange of elements between the different reservoirs of the Earth. In the present chapter we examine atmospheric composition from this broader perspective, and focus more specifically on the biogeochemical factors that regulate the atmospheric abundances of N2, O2, and CO2.

The Earth system (including the Earth and its atmosphere) is an assemblage of atoms of the 92 natural elements. Almost all of these atoms...

10. 7 The Greenhouse Effect
(pp. 115-145)

We examine in this chapter the role played by atmospheric gases in controlling the temperature of the Earth. The main source of heat to the Earth is solar energy, which is transmitted from the Sun to the Earth byradiationand is converted to heat at the Earth’s surface. To balance this input of solar radiation, the Earth itself emits radiation to space. Some of this terrestrial radiation is trapped bygreenhouse gasesand radiated back to the Earth, resulting in the warming of the surface known as thegreenhouse effect. As we will see, trapping of terrestrial radiation by...

11. 8 Aerosols
(pp. 146-156)

Aerosols in the atmosphere have several important environmental effects. They are a respiratory health hazard at the high concentrations found in urban environments. They scatter and absorb visible radiation, limiting visibility. They affect the Earth’s climate both directly (by scattering and absorbing radiation) and indirectly (by serving as nuclei for cloud formation). They provide sites for surface chemistry and condensed-phase chemistry to take place in the atmosphere. We present in this chapter a general description of the processes controlling aerosol abundances and go on to discuss radiative effects in more detail. Chemical effects will be discussed in subsequent chapters.

Atmospheric...

12. 9 Chemical Kinetics
(pp. 157-163)

In the following chapters we will present various chemical reaction mechanisms controlling the abundance of stratospheric ozone, the oxidizing power of the atmosphere, smog, and acid rain. We first review here some basic notions of chemical kinetics.

Abimolecularreaction involves the collision of two reactantsAandBto yield two productsCandD. The collision produces anactivated complex AB* which decomposes rapidly either to the original reactantsAandBor to the productsCandD. The reaction is written

A+B → C+D

and its rate is calculated as

$- \frac{d}{{dt}}[A] = - \frac{d}{{dt}}[B] = \frac{d}{{dt}}[C] = \frac{d}{{dt}}[D] = k[A][B],$

wherekis therate...

13. 10 Stratospheric Ozone
(pp. 164-199)

The stratospheric ozone layer, centered at about 20 km above the surface of the Earth (figure 10-1), protects life on Earth by absorbing UV radiation from the Sun. In this chapter we examine the mechanisms controlling the abundance of ozone in the stratosphere and the effect of human influence.

The presence of a high-altitude ozone layer in the atmosphere was first determined in the 1920s from observations of the solar UV spectrum. A theory for the origin of this ozone layer was proposed in 1930 by a British scientist, Sydney Chapman, and is known as theChapman mechanism. It lays...

14. 11 Oxidizing Power of the Troposphere
(pp. 200-230)

The atmosphere is an oxidizing medium. Many environmentally important trace gases are removed from the atmosphere mainly by oxidation: greenhouse gases such as CH4, toxic combustion gases such as CO, agents for stratospheric O3depletion such as HCFCs, and others. Oxidation in the troposphere is of key importance because the troposphere contains the bulk of atmospheric mass (85%, see section 2.3) and because gases are generally emitted at the surface.

The most abundant oxidants in the Earth’s atmosphere are O2and O3. These oxidants have large bond energies and are hence relatively unreactive except toward radicals (O2only toward highly...

15. 12 Ozone Air Pollution
(pp. 231-244)

So far we have emphasized the beneficial nature of tropospheric O3as the precursor of OH. In surface air, however, O3is toxic to humans and vegetation because it oxidizes biological tissue. As we have seen in chapter 11, O3is produced in the troposphere from the oxidation of CO and hydrocarbons by OH in the presence of NOx. In densely populated regions with high emissions of NOxand hydrocarbons, rapid O3production can take place and result in a surface air pollution problem. In this chapter, we describe the O3pollution problem in the United States, examine the factors...

16. 13 Acid Rain
(pp. 245-256)

Acid rain was discovered in the nineteenth century by Robert Angus Smith, a pharmacist from Manchester (England), who measured high levels of acidity in rain falling over industrial regions of England and contrasted them to the much lower levels he observed in less polluted areas near the coast. Little attention was paid to his work until the 1950s, when biologists noticed an alarming decline of fish populations in the lakes of southern Norway and traced the problem to acid rain. Similar findings were made in the 1960s in North America (the Adirondacks, Ontario, Quebec). These findings spurred intense research to...

17. Numerical Solutions to Problems
(pp. 257-258)
18. Appendix. Physical Data and Units
(pp. 259-260)
19. Index
(pp. 261-266)