Aqueousphase Reaction Rates

Rates of reaction of aqueous-phase species are generally expressed in terms of moles per liter (M) of solution per second. It is often useful to express aqueous-phase reaction rates on the basis of the gas-phase properties, especially when comparing gas-phase and aqueous-phase reaction rates. In this way both rates are expressed on the same basis. To place our discussion on a concrete basis, let us say we have a reaction of S(IV) with a dissolved species A Ra k A(aq) S(IV) (Ms-1) (7.73) where...

Info

(2380-3970) (100-300) (180-550) (100-1600) (37-113) Numbers in parentheses represent the range of estimates. Source WMO (2002). troposphere. Table 2.16 gives the global budget of CH3C1. According to the best estimates, the sinks exceed the sources by 1049 Gg yr 1. It has been suggested that a major, as yet unidentified, source of CH3C1 exists, probably in the tropics. Methyl bromide (CH3Br) is the most abundant atmospheric bromocarbon, responsible for over half of the bromine reaching the...

Halogencontaining Compounds

Atmospheric halogen-containing compounds are referred to by a variety of names Halocarbons a general term referring to halogen-containing organic compounds Chlorofluorocarbons CFCs) the collective name given to a series of halocarbons containing carbon, chlorine, and fluorine atoms Hydrochlorofluorocarbons (HCFCs) halocarbons containing atoms of hydrogen, in addition to carbon, chlorine, and fluorine Hydrofluorocarbons (HFCs) halocarbons containing atoms of hydrogen, in addition to carbon and...

Chemistry of the Troposphere

The troposphere behaves as a chemical reservoir relatively distinct from the stratosphere. Transport of species from the troposphere into the stratosphere is much slower than mixing within the troposphere itself. A myriad of species are emitted at the Earth's surface, and those with chemical lifetimes less than about a year or so are destroyed in the troposphere. Even though solar radiation of the most energetic wavelengths is removed in the stratosphere, light of sufficiently energetic...

Preface To The First Edition

The study of atmospheric chemistry as a scientific discipline goes back to the eighteenth century, when the principal issue was identifying the major chemical components of the atmosphere, nitrogen, oxygen, water, carbon dioxide, and the noble gases. In the late nineteenth and early twentieth centuries attention turned to the so-called trace gases, species present at less than 1 part per million parts of air by volume (1 pmol per mole). We now know that the atmostphere contains a myriad of...

Chemical Families

Consider the following chemical system Compounds A and B react reversibly, and B reacts irreversibly to C. Assume that the reversible reaction is rapid, compared with the timescale of conversion of B to C. Physically, this means that once a molecule of A reacts to form B, B is much more likely to react back to A than to go on to C every once in a while, B does react to form C. In this case, A and B achieve an equilibrium on a short timescale, and this equilibrium slowly adjusts as some of the B...

Ozone Vertical Profiles

Polar Vortex Antarctic

10000 100 200 Ozone Partial Pressure, nbar South Pole (Historical) October y-, Mean 0 100 200 Ozone Partial Pressure, nbar 0 100 200 Ozone Partial Pressure, nbar s-1987 Avg. Other Sept. Oct> S undin8s 1987 * s-1987 Avg. Other Sept. Oct> S undin8s 1987 * 40 80 120 160 Ozone Partial Pressure, nbar 100 200 Ozone Partial Pressure, nbar 0 100 200 Ozone Partial Pressure, nbar FIGURE 5.18 Observations of the change in October total ozone profiles over Antarctica (WMO 1994). Historical data at...

The Size Distribution Function

The atmosphere, whether in urban or remote areas, contains significant concentrations of aerosol particles sometimes as high as 107-108 cm . The diameters of these particles span over four orders of magnitude, from a few nanometers to around 100 pm. To appreciate this wide size range one just needs to consider that the mass of a 10-pm-diameter particle is equivalent to the mass of one billion 10-nm particles. Combustion-generated particles, such as those from automobiles, power generation, and...

PT dp J T dp

But is not a function of pressure and therefore its derivative with respect to pressure is zero, so for an ideal gas Using (10.13), one can calculate the derivative of G with respect to pressure but for a system consisting of n moles of a single gas see (10.18) and therefore from (10.36) and (10.37) Combining (10.35) and (10.38), we see that our definition of an ideal gas entails Deviations from ideal gas behavior are customarily expressed in terms of the compressibility factor C pV (nRT). Both...

PH

FIGURE 7.A.3 Sulfate production rate from the S IV -OH reaction as a function of pH for a mixing ratio of S02 g 1 ppb and OH aq 1 x 1012 M at 298 K. The sulfate radicals SOJ and SOj participate in a series of additional reactions in ambient clouds that complicate even further the above chain and modify significantly the overall reaction rate. These reactions are discussed subsequently. 7.A.2 Oxidation of S IV by Oxides of Nitrogen Nitrogen dioxide has limited water solubility and its resulting...

Summer Lower Stratosphere

Wcmk BTJC UJQJC Unnng jad mi jmlcwaid xjhI jiflWflWBPi IftlHfWt FIGURE 5,34 Stratospheric transport and mixing UK National Environment Research Council . Temperature isotherms arc labeled as potential temperature. Potential temperature 0 at any altitude z is the temperature of an air parcel brought from that altitude adiabatically to the surface. It can be calculated from the relation 6 T p pQ '7, where T and p are the temperature and pressure at altitude and po is the surface pressure, usually...

DM ka[A[B

As the product molecule AB becomes more complex, the value of kr decreases because the combination energy is distributed among more and more vibrational modes. The concentration of the third body, M , is usually related directly to the pressure since in the atmosphere M is the sum of N2 and 02. The concentration of M at which the reaction rate behavior changes from third-order to second-order is lower the more complex the product molecule. Combination of two hydrogen atoms to form H2 is...

Vertical Variation

The vertical distribution of aerosol mass concentration typically shows an exponential decrease with altitude up to a height Hp and a rather constant profile above that altitude Gras 1991 . The aerosol mass concentration as a function of height can then be expressed as where M 0 is the surface concentration and Hp the scale height. Jaenicke 1993 proposed values of Hp equal to 900 m for the marine, 730 m for the remote continental, 2000 m for the desert, and 30,000 m for the polar aerosol types....

Spatial And Temporal Variation

Narsto Pie Charts

The concentration of atmospheric aerosols varies considerably in space and time. This variability of the aerosol concentration field is determined by meteorology and the emissions of aerosols and their precursors. For example, the annual average concentration of PM2 5 in North America varies by more than an order of magnitude as one moves from the clean remote to the polluted urban areas of Mexico City and southern California Figure 8.24 . Sulfate dominates the fine aerosol composition in the...

Cio hohoci o

In addition, the following HOx BrOA and Br0t C10t cycles are important in the lower stratosphere 20 km HOx BrOx cycle 1 Br O3 gt BrO 02 OH 03 gt H02 02 BrO H02 gt HOBr 02 HOBr hv OH Br BrO CIO gt BrCl 02 BrCl hv Br CI BrO ClO cycle 2 Br 03 gt BrO 02 Cl 03 C10 02 BrO CIO ClOO Br C100 M- Cl 02 While there is a total chlorine compound mixing ratio in the stratosphere of approximately 3400 ppt, that for bromine gases is only 20 ppt Figure 5.1 . Remarkably, with 150 times less abundance than...

Atmospheric Trace Constituents

Virtually every element in the periodic table is found in the atmosphere however, when classifying atmospheric species according to chemical composition, it proves to be convenient to use a small number of major groupings such as 1. Sulfur-containing compounds. 2. Nitrogen-containing compounds. 3. Carbon-containing compounds. 4. Halogen-containing compounds. Obviously these categories are not exclusive many sulfur-containing compounds, for example, also include atoms of carbon. And virtually...

DUTdSpdV Jidni

The chemical potential p, has an important function in the system's thermodynamic behavior analogous to pressure or temperature. A temperature difference between two bodies determines the tendency of heat to pass from one body to another while a pressure difference determines the tendency for bodily movement. We will show that a difference in chemical potential can be viewed as the cause for chemical reaction or for mass transfer from one phase to another. The chemical potential p, greatly...

Tropospheric Chemistry Of Halogen Compounds

Chemical Reaction Volcano Eruption

Halogen compounds arise in the troposphere from the chemical degradation of partially halogenated organic compounds that originate from a variety of natural and anthropogenic sources and by the liberation of halogen compounds from seasalt aerosol. Natural sources of gaseous halocarbons include the oceans, which release methyl halides CH3C1, CH3Br, and CH3I and polyhalogenated species CHBr3, CH2Br2 . Methyl halides, notably CH3Br, are also produced by biomass burning. Industrial replacements for...

1

FIGURE 8.9 Fitting of an urban aerosol number distribution with a power-law distribution left and comparison of the corresponding volume distributions right . Even if the power-law distribution appears to match the number distribution, it fails to reproduce he volume distribution. Leaitch and Isaac 1991 . However, the power-law function is a monotonically decreasing function. We have already seen e.g., in Figure 8.6 that this is not the case for ambient aerosol size distributions that have...

Spatial And Temporal Scales Of Atmospheric Processes

Gases are produced by chemical processes within the atmosphere itself, by biological activity, volcanic exhalation, radioactive decay, and human industrial activities. Gases are removed from the atmosphere by chemical reactions in the atmosphere, by biological activity, by physical processes in the atmosphere such as particle formation , and by deposition and uptake by the oceans and land masses. The average lifetime of a gas molecule introduced into the...

Properties Of The Atmospheric Aerosol

The total surface area S, of the aerosol per cm3 of air is then S, n D2nN Dp dDp ns Dp dDp pm2cm3 Jo Jo and is equal to the area below the ns Dp curve in Figure 8.4. The aerosol volume distribution nv Dp can be defined as nv Dp dDp volume of particles per cm3 of air having diameters in the range Dp to Dp dDp The total aerosol volume per cm3 of air V, is v, - DlnN Dp dDp nv Dp dDp pm3cnr3 o Jo Jo and is equal to the area below the ny Dp curve in Figure 8.4. If the particles all have density pp g...

Atmospheric Chemistry Of Reduced Nitrogen Compounds

Reduced nitrogen compounds emitted into the atmosphere include ammonia NH3 , hydrogen cyanide HCN , and possibly their higher homologs such as the aliphatic and aromatic amines RNH2, RR'NH, and RR'RN and the nitriles RCN, where R, R', R alkyl or aryl group. The major gas-phase atmospheric reactions of the amines involve the OH radical nh3 oh- h20 nh2-ch3nh2 oh- h20 ch3nh ch3 2nh oh- gt h20 ch3 2n- gt h20 ch2nhch3 Amines also react with gaseous nitric acid to form the corresponding nitrate...

Ii

Jaenicke Tropospheric Aerosols

FIGURE 8.18 Typical remote continental aerosol number, surface, and volume distributions. FIGURE 8.18 Typical remote continental aerosol number, surface, and volume distributions. FIGURE 8.19 Typical free tropospheric aerosol number, surface, and volume distributions. more particles in the accumulation mode relative to lower tropospheric spectra, suggesting precipitation scavenging and deposition of smaller and larger particles Leaitch and Isaac 1991 . The low temperature and low aerosol...

Radiative Flux In The Atmosphere

The essential energy flux in atmospheric chemistry is the flux of solar radiation. The radiant flux density F is the radiant energy flux across any surface element, without consideration of the direction F is measured in watts per square meter W m 2 . The radiant flux density is called the irradiance E when the radiation is received on a surface. Thus F and E are often used interchangeably. We will use F in general and E when we are referring specifically to the radiant flux density on a...

Beerlambert Law And Optical Depth

Consider the propagation of radiation of wavelength X through a layer of thickness dx perpendicular to a beam of intensity F X . The extinction of radiation on traversing an infinitesimal pathlength dx is linearly proportional to the amount of matter along the path F x dx,X - F x,X -b x,X F x,X dx 4.17 where b x,X units of inverse length is called the extinction coefficient and is proportional to the density of material in the medium. Extinction includes both absorption and scattering, each of...

Atmospheric Radiation and Photochemistry

Atmospheric Chemistry

Basically all the energy that reaches the Earth comes from the Sun. The absorption and loss of radiant energy by the Earth and the atmosphere are almost totally responsible for the Earth's weather on both global and local scales. The average temperature on the Earth remains fairly constant, indicating that the Earth and the atmosphere on the whole lose as much energy by reradiation back into space as is received by radiation from the Sun. The accounting for the incoming and outgoing radiant...

Nt

Where the z coordinate is taken as vertically upward. The solution of 9.80 and 9.81 for the vertical profile of the number distribution We can calculate the deposition rate of particles on the z 0 surface from the expression for the flux of particles at z 0, Recall that N 0,t 0 in 9.83 . Combining 9.82 and 9,83 we obtain According to 9.84 , there is an infinite removal flux at r 0, bccause of our artificial specification of an infinite concentration gradient at z t 0. We can identify a...

The Pseudosteadystate Approximation

Many chemical reactions involve very reactive intermediate species such as free radicals, which, as a result of their high reactivity, are consumed virtually as rapidly as they are formed and consequently exist at very low concentrations. The pseudo-steady-state approximation1 PSSA is a fundamental way of dealing with such reactive intermediates when deriving the overall rate of a chemical reaction mechanism. It is perhaps easiest to explain the PSSA by way of an example. Consider the...

Aerosol Chemical Composition

Effect Hydrogen Iron Particle

Atmospheric aerosol particles contain sulfates, nitrates, ammonium, organic material, crustal species, seasalt, metal oxides, hydrogen ions, and water. From these species sulfate, ammonium, organic and elemental carbon, and certain transition metals are found predominantly in the fine particles. Crustal materials, including silicon, calcium, magnesium, aluminum, and iron, and biogenic organic particles pollen, spores, plant fragments are usually in the coarse aerosol fraction. Nitrate can be...

NO ppt

FIGURE 6.7 Calculated 24-h average 03 production and loss rates for the free troposphere above Hawaii during the MLOPEX as a function of the NO mixing ratio Liu et al. 1992 . Figure 6.7 shows calculated, 24-hour-average production and loss rates for the free troposphere above Hawaii during the MLOPEX Mauna Loa Photochemistry Experiment as a function of NO mixing ratio. The 03 loss rate is seen to be almost independent of NO , at about 5 x 105 molecules cm-3 s_1. For an 03 mixing ratio of 40...

Idealised Schematic Of The Distribution Of Surface Area Of An Atmospheric Aerosol Whitby And Cantrell 1976

_ Transient Nuclei or _ Aitken Nuclei Range Mechanically Generated_ Aerosol Range FIGURE 2.7 Idealized schematic of the distribution of particle surface area of an atmospheric aerosol Whitby and Cantrell 1976 . Principal modes, sources, and particle formation and removal mechanisms are indicated. preponderance of particles by number because of their small size, these particles rarely account for more than a few percent of the total mass of airborne particles. Particles in the nuclei mode are...

Aji

Hence the activity of water decreases as electrolyte 2 is added to the system, until the solution becomes saturated in that electrolyte, too. The aerosol is exposed to the atmosphere and therefore its DRH also decreases. The preceding analysis can be extended to aerosols containing more than two salts. Thus one can prove that water activity reaches a minimum at the deliquescence point of the aerosol. Another consequence of this analysis is that the DRH of a mixed salt is always lower than the...

Atmospheric Chemistry Of Methane

The principal oxidation reaction of methane, CH4, is with the hydroxyl radical CH4 OH CH3 H20 reaction 1 As in the case of the hydrogen atom, the methyl radical, CH3, reacts virtually instantaneously with 02 to yield the methyl peroxy radical, CH302 so that the CH4-OH reaction may be written concisely as The rate coefficient for reaction 1 is k 2.45 x 10 12 exp -1775 T cm3 molecule1 s_1. At T 273 K and OH 106 molecules cm3, the lifetime of CH4 against OH reaction is about 9 years. Despite its...

Appendix Oxygen And Hydrogen Chemistry

Ozone is not produced at all in the aqueous phase, but at least 12 different chemical pathways consuming ozone have been identified. Because of the limited aqueous-phase solubility of ozone, none of these reactions is rapid enough to influence directly the gas-phase ozone concentration Pandis and Seinfeld 1989a . The fastest of these reactions is that with the 02 radical resulting from the dissociation of H02 reaction 7.69 03 aq 02 OH 202 OH 7.A.40 Although the rate of this reaction is...

Spyros N Pandis

University of Patras and Carnegie Mellon University Copyright 2006 by John Wiley amp Sons, Inc. All rights reserved Published by John Wiley amp Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without...

Aocfch

Table 5.3 presents ozone depletion potentials calculated with two-dimensional models, as presented by the World Meteorological Organization 2002 . Tropospheric OH reaction is the primary sink for the hydrogen-containing species. As seen in Table 5.3, the ODPs for the hydrogen-containing species are considerably smaller than those of the CFCs, the difference reflecting the more effective chemical removal in the troposphere. Although Table 5.3 gives the ODPs of several brominated halocarbons...

Nitrogencontaining Compounds

The strong triple bond of the N N molecule makes it practically inert it is extremely stable chemically and is not involved in the chemistry of the troposphere or stratosphere. The important nitrogen-containing trace species in the atmosphere are nitrous oxide N20 , nitric oxide NO , nitrogen dioxide N02 , nitric acid HN03 , and ammonia NH3 . The first of these, nitrous oxide N20 , is a colorless gas that is emitted almost totally by natural sources, principally by bacterial action in the soil....

Gravitational Settling Of An Aerosol Particle

Aerosol Settling Speed

Up to this point, we have considered the drag force on a particle moving at a steady velocity Mqo through a quiescent fluid. Recall that this case is equivalent to the flow of a fluid at velocity past the stationary particle. The motion of the particle, however, arises in the first place because of the action of some external force on the particle such as gravity. The drag force arises as soon as there is a difference between the velocity of the particle and that of the fluid. The basis of the...

Pzg

Where p z is the mass density of air at height z and g is the acceleration due to gravity. From the ideal-gas law, we obtain where Mair is the average molecular weight of air 28.97 g mol-1 . Thus where H z RT z M.dirg is a characteristic length scale for decrease of pressure with height. The temperature in the atmosphere varies by less than a factor of 2, while the pressure changes by six orders of magnitude see Table A.8 . If the temperature can be taken to be approximately constant, just to...

W lexp[afci

The characteristic approach time of this solution to its steady state is Applying this to 5.11 , we find the characteristic time needed to establish the 03 steady state is given by Although j0l and y'o, decrease as altitude decreases, the exponential increase of M with decreasing altitude exerts the dominate influence on xg3. Thus, we expect this time scale to increase at lower altitudes. Let us estimate Tq, as a function of altitude, at a solar zenith angle of 0 Again, we caution that x is not...

Formic Acid Henrys Law Constant

And this concentration ratio remains less than 10-4 for pH values less than 7.5. Therefore, for most atmospheric applications, the dissociation of dissolved hydrogen peroxide can be neglected. The equilibrium partitioning of H202 between the gas and aqueous phases can be calculated from 7.9 using the Henry's law coefficient h2o, and is shown in Figure 7.12. H202 exists in appreciable amounts in both the gas and aqueous phases inside a typical cloud. For example, for a cloud liquid water content...

Od mo m

The rate coefficient for this reaction is Table B.2 Vd m 3-2 x 10-11 exp 70 r M 02 1.8 x 10'nexp 110 r M N2 The mean lifetime of O 'D against reaction with M is Choosing 30 km T 227 K , and noting that M consists of 0.2102 0.79 N2, M 3.1 x 1017 molecules cm-3 Table 5.1 , we obtain Consequently, O 'D is effectively converted instantaeously to ground-state O, and the photodissociation of 03 by both reactions 3 and 3' above can be considered to produce entirely ground-state O atoms. Finally, O and...

Ni J r RT

And the collision theory bimolecular rate coefficient is As indicated, the terms multiplying the exponential are customarily denoted by A, the collision frequency factor, or simply the preexponential factor. Thus, the reaction rate coefficient consists of two components, the frequency with which the reactants collide and the fraction of collisions that have enough energy to overcome the barrier to reaction. The quantity 8 cB7' 7iji ' 2 is a molecular speed at ordinary temperatures its value is...

Actinic Flux

Sunlight drives the chemistry of the atmosphere by dissociating a number of molecules into fragments that are often highly reactive. Whether a molecule can be dissociated in the atmosphere depends on the probability of an encounter between a photon of appropriate energy and the molecule. The radiative quantity pertinent for photochemical reactions is the photon flux incident on the molecule from all directions, since it does not matter to the molecule from which direction a photon comes. The...

Thermodynamic Principles

An atmospheric air parcel can be viewed thermodynamically as a homogeneous system that may exchange energy, work, and mass with its surroundings. Let us assume that an air parcel contains k chemical species and has a temperature T, pressure p, and volume V. There are n, moles of species i in the parcel. The first section of this chapter is a review of fundamental chemical thermodynamic principles focusing on the chemical potential of species in the gas, aqueous, and solid phases. Further...

Absorption Of Radiation By Atmospheric Gases

Spectra Atmospheric Absorption H2o

Figure 4.9 shows the solar irradiance at the top of the atmosphere and that at sea level. The absorption spectra are quite complex, but they do indicate that absorption is so strong in some spectral regions that no solar energy in those regions reaches the surface of the Earth. As we will see, absorption by 02 and 03 is responsible for removal of practically all the incident radiation with wavelengths shorter than 290 nm. On the other hand, atmospheric absorption is not strong from 300 to about...

Liquid Water Content g m

Henry Constant For So2

FIGURE 7.2 Frequency distribution for liquid water content average values for various cloud types over Europe and Asia. The equilibrium between gaseous and dissolved A is usually expressed by the so-called Henry's law coefficient HA where pA is the partial pressure of A in the gas phase atm and A aq is the aqueous-phase concentration of A mol L ' in equilibrium with pA. The customary units of the Henry's law coefficient HA are mol L-1 atm-1. The unit mol L_1 is usually written as M, a notation...

Dynamic Behavior Of Solutions With Aqueousphase Chemical Reactions

To compare the rates of various aqueous-phase chemical reactions we have been calculating instantaneous rates of conversion as a function of solution pH. In the atmosphere a droplet is formed, usually by nucleation around a particle, and is subsequently exposed to an environment containing reactive gases. Gases then dissolve in the droplet, establishing an initial pH and composition. Aqueous-phase reactions ensue and the pH and composition of the droplet start changing accordingly. In this...

Atmospheric Ozone

Atmospheric Aerosol Processes

Ozone 03 is a reactive oxidant gas produced naturally in trace amounts in the Earth's atmosphere. Ozone was discovered by C. F. Schonbein in the middle of the nineteenth century he also was first to detect ozone in air Schonbein 1840, 1854 . Schonbein 1840 suggested the presence of an atmospheric gas having a peculiar odor the Greek word for to smell is ozeiri . Spectroscopic studies in the late nineteenth century showed that ozone is present at a higher mixing ratio in the upper atmospheric...

Aerosol Liquid Water Content

Water is an important component of atmospheric aerosols. Most of the water associated with atmospheric particles is chemically unbound Pilinis et at. 1989 . At very low relative FIGURE 10.4 Diameter change of NH4 2S04, NH4HS04, and H2S04 particles as a function of relative humidity. Dpo is the diameter of the particle at 0 RH. humidities, atmospheric aerosol particles containing inorganic salts are solid. As the ambient relative humidity increases, the particles remain solid until the relative...

Brownian Motion Of Aerosol Particles

Brownian Diffusion

Particles suspended in a fluid are continuously bombarded by the surrounding fluid molecules. This constant bombardment results in a random motion of the particles known as Brownian motion. A satisfactory description of this irregular motion random walk can be obtained ignoring the detailed structure of the particle-fluid molecule interaction if we assume that what happens to the aerosol fluid system at a given time t depends only on the system state at time t. Stochastic processes with this...

Motion Of An Aerosol Particle In An External Force Field

The force balance presented in 9.35 describes the motion of a particle in a force field. As long as the particle is not moving in a vacuum, the drag force will always be present, so let us remove the drag force from the summation of forces where F denotes external force i those forces arising from external potential fields, such as gravity and electrical forces . Situations in which a charged particle moves in an electric field are important in several gas-cleaning devices and aerosol...

The Layers Of The Atmosphere

-100 -80 -60 -40 -20 0 20 40 Temperature, C FIGURE 1.1 Layers of the atmosphere. about 217 K -56 C . The troposphere can be divided into the planetary boundary layer, extending from the Earth's surface up to about 1 km, and the free troposphere, extending from about 1 km to the tropopause. As air moves vertically, its temperature changes in response to the local pressure. For dry air, this rate of change is substantial, about 1 C per 100 m the theory behind this will be developed in Chapter 16...

Dynamics of Single Aerosol Particles

Mean Free Path Against Altitude

In this chapter, we focus on the processes involving a single aerosol particle in a suspending fluid and the interaction of the particle with the suspending fluid itself. We begin by considering how to characterize the size of the particle in an appropriate way in order to describe transport processes involving momentum, mass, and energy. We then treat the drag force exerted by the fluid on the particle, the motion of a particle through a fluid due to an imposed external force and resulting...

Chemistry Of Nonmethane Organic Compounds In The Troposphere

The essential elements of tropospheric chemistry have been presented in Sections 6.1-6.9. The remainder of this chapter is devoted to an in-depth treatment of the tropospheric chemistry of individual classes of organic species. For many readers, for example, those in a first course in atmospheric chemistry, it may not be necessary to proceed beyond this point in this chapter. All problems at the end of the chapter can be answered based on the material in Sections 6.1-6.9. There are a number of...

Overview Of Stratospheric Chemistry

About 90 of the atmosphere's ozone is found in the stratosphere, residing in what is commonly referred to as the ozone layer. At the peak of the ozone layer the 03 mixing ratio is about 12ppm. The total amount of 03 in the Earth's atmosphere is not great if all the 03 molecules in the troposphere and stratosphere were brought down to the Earth's Atmospheric Chemistry and Physics From Air Pollution to Climate Change, Second Edition, by John H. Seinfeld and Spyros N. Pandis. Copyright 2006 John...

Preface To The Second Edition

Two considerations motivated us to undertake the Second Edition of this book. First, a number of important developments have occurred in atmospheric science since 1998, the year of the First Edition, and we wanted to update the treatments in several areas of the book to reflect these advances in understanding of atmospheric processes. New chapters have been added on chemical kinetics, atmospheric radiation and photochemistry, global circulation of the atmosphere, and global biogeochemical...

Order Of Reaction

We will consider three types of chemical reaction First-order unimolecular A gt B C Second-order bimolecular A B gt C D Third-order termolecular A B M gt AB M The rate in molecules cm 3 s ' of a first-order reaction is expressed as where the first-order rate coefficient k has units of s_1 reciprocal seconds . Few reactions are truly first-order, in that they involve decomposition of a molecule without intervention of a second molecule. The classic example of a true first-order reaction is...

Appendix Free Radicals

Free radicals are characterized by an odd number of electrons, an unpaired electron in the outer valence shell. These species are exceptionally reactive, as they are always seeking to pair off their lone election. Free radicals play a central role in atmospheric chemistry in both the stratosphere and the troposphere. Important radicals include, for example, OH and H02 both stratosphere and troposphere and CI and CIO stratosphere . One can represent the bonding in molecules using the Lewis dot...

M[CM[Cly

Any process that even modestly shifts the balance away from the reservoir species to CIO can have a large impact on ozone depletion. In the midlatitude lower stratosphere the concentration of CIO is actually controlled by the amount of C10N02 present Note that the O atom concentration in the lower stratosphere is too low for its reaction with CIO to compete effectively with the C10 N02 reaction. The HOJf NO,-, and CIO cycles are all coupled to one another, and their interrelationships strongly...

Nhno Nh No J

Is at equilibrium and therefore the chemical potential of NH4NO3 satisfies I h4no3 Hnh4 NO3- RT The binary activity coefficient for NH4N03 can be defined as l nhinoj nh4 m noj rt ln ynh4n03'nnh 'n03 If the electrolyte dissociates completely and the initial molality of NH4N03 is 'W il,no,. then HnH4N03 MSh N03- RT ln YNH4N03WNH4N03 10-57 The equilibrium expression 10.28 can be used to obtain a useful expression for aerosol equilibrium calculations. Let us consider the general reaction Then...

A [h

With k 7.5 1.16 x 107 M 2 s_1 and K 13 M1 at 298 K. Noting that H202 is a very weak electrolyte, that H HSOj so2 si so2, and that, for pH gt 2, 1 A H 1, one concludes that the rate of this reaction is practically pH independent over the pH range of atmospheric interest. For a H202 g mixing ratio of 1 ppb the rate is roughly 300pMlr1 ppb S02r' 700 S02 g h1 gwater m3 air 1 . The near pH independence can also be viewed that the pH dependences of the S IV solubility and of the reaction rate...

Equivalent Particle Diameters

Up to this point we have considered spherical particles of a known diameter Dp and density pp. Atmospheric particles are sometimes nonspherical and we seldom have information about their density. Also a number of techniques used for atomospheric aerosol size measurement actually measure the particle's terminal velocity or its electrical mobility. In these cases we need to define an equivalent diameter for the nonspherical particles or even for the spherical particles of unknown density or...

Tropospheric Reservoir Molecules

Atmospheric Chemistry

In the CO oxidation cycle, hydrogen peroxide, H202, is a reservoir molecule for HOt In the CH4 oxidation cycle, methyl hydroperoxide, CH3OOH, is also a HO reservoir Nitrous acid, HONO, which is formed by a heterogeneous reaction involving NO and H20 Calvert et al. 1994 , is a reservoir for both HO, and NO,. HONO dissociates by photolysis to regenerate OH atid NO Formed overnight, HONO photo dissociates upon sunrise to inject a pulse of OH into the early-morning atmosphere. The class of...

D

Figure 4.9 a Solar spectral irradiance at the top of the atmosphere and at sea level. Shaded regions indicate the molecules responsible for absorption. Absorption spectra for b molecular oxygen and ozone, c water vapor, and d the atmosphere, expressed on a scale of 0-1.

Photolysis Rate As A Function Of Altitude

Effect Cloud Photolysis Rate

Photolysis reactions are central to atmospheric chemistry, since the source of energy that drives the entire system of atmospheric reactions is the Sun. The general expression for the first-order rate coefficient jA for photodissociation of a species A is given by 4.39 . Because the rate of a photolysis reaction depends on the spectral actinic flux I and because photolysis rate as a function of altitude the spectral actinic flux varies with altitude in the atmosphere, the rate of photolysis...

[h[hco

C02 H20 7-18 _ H CQ2 where Khc is the equilibrium constant for the hydrolysis of C02, and Kc and Kc2 denote the first and second dissociation equilibrium constants for dissolved C02. Note that liquid water concentration has already been incorporated into the hydrolysis constant and that Khr is identical to the Henry's law coefficient for carbon dioxide, Hco2- aqueous-phase chemical equilibria The concentrations of the species in solution are given by The total dissolved carbon dioxide C02 is...

Hno

Figure 5.24 shows a distribution of stratospheric aerosol surface area as a function of altitude from 18 to 30 km inferred from satellite measurements. The surface area units used in Figure 5.24 are cm2 cm3, and typical values of the stratospheric surface area at, say, 18 km altitude are about 0.8 x 10 8 cm2 cm-3. This is equivalent to 0.8pm2 cm3. As a useful rule of thumb, stratospheric aerosol surface area in the lower stratosphere ranges between 0.5 and 1.0 pm2 cm-3. Figure 5.25 depicts the...

Liquid Water In The Atmosphere

Water Atmosphere Ghz

Water is abundant on our planet, distinguishing Earth from all other planets in the solar system. More than 97 of Earth s water is in the oceans, with 2.1 in the polar ice caps and 0.6 in aquifers. The atmosphere contains only about one part in a hundred thousand 0.001 of Earth s available water. However, the transport and phase distribution of this relatively small amount of water estimated total liquid equivalent volume of 13,000 km3 are some of the most important features of Earth s climate....

Appendix Air Pollution Legislation

The legislative basis for air pollution abatement in the United States is the 1963 Clean Air Act and its amendments. The Clean Air Act was the first modern environmental law enacted by the U.S. Congress. The original act was signed into law in 1963, and major amendments were made in 1970, 1977, and 1990. The act establishes the federal-state relationship that requires the U.S. Environmental Protection Agency EPA to develop National Ambient Air-Quality Standards NAAQS and empowers the states to...

Show That 1 Ppm Co2 In The Atmosphere Corresponds To 2.1 Pg Carbon And Therefore That The Current Atmospheric Level Of

- Inter-hemispheric Mixing Time - Intra-hemispheric Mixing Time lm 10 m 100 m 1km 10 km 100 km 1000 km 10,000 km Spatial Scale FIGURE 1.4 Spatial and temporal scales of variability for atmospheric constituents. dimensions. Four rough categories have proved convenient to classify atmospheric scales of motion 1. Microscale. Phenomena occurring on scales of the order of 0-100 m, such as the meandering and dispersion of a chimney plume and the complicated flow regime in the wake of a large...