Tropospheric Chemistry Of Halogen Compounds
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...
I 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 1
of physical and chemical 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 1
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...
Theories Of Chemical Kinetics
A basic goal of the theory of chemical kinetics is to predict the magnitude of the reaction rate coefficient and its temperature dependence. We focus first on bimolecular reactions. The most elementary approach to bimolecular reactions is based on the collision of hard, structureless spheres. This approach is called collision theory. Imagine that the molecules are like billiard balls, in that there is no interaction between them until they come into contact, and they are impenetrable, so that...
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...
Iii Ii
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
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 1
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
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...
Info Uwp
Figure 6.3 shows the ozone production efficiency for CO oxidation at 298 K at the Earth's surface as a function of NO NO N02 for NO mixing ratios from 1 ppt to lOOppb. At the ground-level conditions of Figure 6.3, we assume that pho, 1 ppts-1, that N0 N02 0.1, and a CO mixing ratio of 200 ppb. The OPE is largest at the lowest concentration of NO at these low levels, NO termination by OH N02 is suppressed and each NO participates in more 03 production cycles. At 100 ppb NO , OPE approaches zero,...
Idealised Schematic Of The Distribution Of Surface Area Of An Atmospheric
_ 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
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...
Info Buo
i I r I I I I I I I I I I I I I I 1 i I r ' ' ' I I I lt I I I I I ' ' I Ti I I I I I I FIGURE 7.4 Effective Henry's law constant for C02 as a function of the solution pH. Also shown is the corresponding equilibrium total dissolved C02 concentration COj for a C02 mixing ratio of 330 ppm. which can be used to calculate H , Using 7.12 , 7.21 , and 7.22 for OH , HCOj , and CO2 , respectively, we can place 7.27 in the form of an equation with a single unknown, the hydrogen ion concentration H 3 -...
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...
Info Gah
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. Similar arguments hold for ozone however, nitrogen and oxygen are symmetric and thus are not strongly affected by radiation above 400 nm. The C02 molecule is linear but can easily be bent, leading to an induced dipole moment. A...
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
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
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
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
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...
Info Fzf
m - Ethyl toluene p - Ethyl toluene Aromatic compounds of interest in tropospheric chemistry. m - Ethyl toluene p - Ethyl toluene Aromatic compounds of interest in tropospheric chemistry. The aromatic-OH radical reaction proceeds via two pathways a a minor one of order 10 involving H-atom abstraction from C H bonds of, for benzene, the aromatic ring, or for alkyl-substituted aromatic hydrocarbons, the alkyl-substituent groups and b a major reaction pathway of order 90 involving OH radical...
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 1
-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
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...
Info Off
2.2-3.0 1.4 1.1 15-25 8.4 11.6 0.01-2 0.8 0.2 0.25-0.78 0.3 0.2 c Numbers in parentheses are fluxes from Northern Hemisphere Southern Hemisphere. Hemisphere. Figure 2.1 shows estimates of global anthropogenic sulfur emissions since 1850, and Table 2.3 summarizes observed mixing ratios and atmospheric lifetimes of atmospheric sulfur gases. Dimethyl sulfide DMS is the dominant sulfur compound emitted from the world's oceans. DMS was first measured in the surface ocean by Lovelock et al. 1972 ,...
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...