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6 Chemistry The production of nitric oxide by nuclear explosions and the production of soot and gaseous pollutants by fires ignited by nuclear explosions would pose chemical threats to the atmosphere in the postnuclear war period. This chapter first discusses the generation of the polluting substances and then assesses their impacts in the atmosphere. GASEOUS EMISSIONS FROM NUCLEAR FIREBALLS AND NUCLEAR WAR FIRES Nitric Oxide Nuclear explosions produce nitric oxide (NO) by heating air to very high temperatures both in the interior of the fireball and in the accompanying shock wave. At temperatures above about 2000 K the equilibrium N2 + O2 = 2NO is rapidly established, the amount of NO increasing with increasing temperature. As hot air containing large amounts of NO is cooled, the above equilibrium is maintained until a temperature is reached where the rates of the reactions maintaining the equilibrium become slow in comparison with the cooling rate. For cooling times of seconds to milliseconds, the NO concentration "freezes" (becomes fixed) at temperatures between 1700 K and 2500 K, corresponding to NO concentrations of 0.3 and 2.0 percent by volume, respectively. There have been numerous estimates of the amount of NO produced per megaton of explosion energy, and these have been reviewed by Gilmore (19751. The spherical shock wave is estimated to produce 0.8 x 1032 NO molecules per megaton of explosive yield, as a result of the rapid heating of air in the shock front followed by rapid cooling due to expansion and radiative emission. The shock wave calculation of NO production does not take into account the fact that air remaining within the fireball center contains approximately one-sixth of the initial explosion energy. This air cools on a time scale of several seconds by further radiative emission, entrainment of cold air, and expansion as it rises to higher 107

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108 altitudes. These mechanisms are sufficiently complex that one can only estimate upper and lower limits to the quantity of NO finally produced. A lower limit to the amount of NO finally produced may be obtained by assuming that all of the shock-heated air is entrained by the fireball and (again) heated to a temperature high enough to reach equilibrium. This is possible since the thickness of the ~shell. of shock-heated air containing NO is smaller than the radius of the fireball. To minimize the cooling rate, and thus the freeze-out temperature, it is assumed that this air mass cools only by adiabatic expansion as the fireball rises and by using a minimum rise velocity. The resulting lower limit to NO production is 0.4 x 1032 molecules per megaton. Since the interior of the fireball is much hotter than the surrounding shock-heated air, it will rise much faster and possibly pierce the shell of shock-heated air to mix with the cold, undisturbed air above it. Thus an upper limit to NO production may be obtained by assuming that none of the 0.8 x 1032 NO molecules per megaton produced in the shock wave are entrained by the hot fireball and that the interior is cooled totally by entrainment of cold, undisturbed air to produce additional NO. The under limit to total NO Production is then estimated to be 1.5 x 1032 molecules per megaton. One can make strong arguments that both the lower and the upper limits are extremely unlikely. For the purposes of this assessment, a NO yield of 1.0 x 1032 molecules per megaton (0.005 Tg/Mt) is assumed. It should be emphasized that the emission factor for nitrogen oxides produced in nuclear explosions is based wholly on theoretical considerations and that there has not yet been any attempt at experimental verification of the amounts produced. Sedlacek et al. (1983), analyzing samples for HNO3 in the stratosphere, infer that the Chinese 4-Mt nuclear device of 1976 produced about 10 times the amount of NO as expected from the theoretical calculations discussed above. The discrepancy remains unexplained. Table 6.1 gives the calculated total amounts of NO injected by the two scenarios of this study as well as amounts used in other studies. Fire Emissions Uncontrolled fires result in incomplete combustion with emissions of copious quantities of both particulate and gaseous matter. The per tabulate emissions and their effects on the physical properties of the atmosphere are dealt with in other sections of this report. Among the gaseous emissions from fires are carbon monoxide, nitrogen oxides, and a large number of hydrocarbons and other organic compounds. These compounds, together with sunlight, are the necessary ingredients for photochemical smog formation.

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109 TABLE 6.1 Recent Estimates of Maximal Ozone Depletion Resulting from a Nuclear War NO (1032 molecules) Maximum Ozone Depletion (percent) Note Yield Below Above Scenario (Mt) 12 km 12 km Baseline 6,5002,665 3,835 17 a Excursion 8,5002,665 5,835 43 b Chang Case A 10,600560 6,540 51 ~ Chang Case B 5,300280 3,270 32 d Chang Case C 5,6700 3,800 42 e Chang Case D 4,930560 2,740 16 f Chang Case E 6,720180 4,340 39 g Chang Case F 3,890390 2,220 20 h Ambio 5,7404,510 1,230 ~0 i Ambio Excursion 10,0001,375 8,625 65 (45N) j l Turco et al. 10,0001,200 8,400 50 k (1983) aNo weapons larger than 1.5 Mt. See Chapter 3 for details. bBaseline scenario plus 100 weapons of 20-Mt yield. CAll strategic weapons in the United States and USSR arsenals successfully detonated. dHalf of the weapons of each type in the strategic arsenals of the United States and USSR. eAll weapons with individual yields greater than 0.8 Mt in the strategic arsenals of the United States and USSR. fall weapons with individual yields less than or equal to 0.8 Mt in the strategic arsenals of the United States and USSR. gall weapons in the Soviet strategic arsenal. hall weapons in the U.S. strategic arsenal. Then the troposphere is included, the Ambio scenario actually results in a slight ozone increase. The Chang model also gives ~ _ result for the Ambio scenario. . The Ambio excursion scenario consists of 5000 1-Mt detonations plus 500 10-Mt detonations and is identical to the NRC (1975) scenario. kThe blocking of sunlight by nuclear dust and soot was accounted for, but the resulting heating of the stratosphere was not. Carbon Monoxide Carbon monoxide (CO) is the most abundant air pollutant from fires. The emission factor may be quite high, depending on the degree of aeration. For example, Sandberg et al. (1975) measured CO emissions the range of 25 to 40 percent in very low intensity laboratory fires and Ryan and McMahon (1976) state that CO emissions may approach 25

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110 percent for smoldering fires in damp fuels.* Emissions from prescribed forest fires fall in the range of 1 to 25 percent according to Tangren et al. (19761. A review by Chi et al. (1979) recommends an emission factor of 5.6 + 1.6 percent for prescribed fires where the indicated error is the 95 percent confidence interval of the mean. The committee has adopted an emission factor for CO of 5 percent for its calculations. For the baseline scenario in which 4500 Tg of fuel is consumed by fire, the CO emission is 225 Tg. Mixed uniformly throughout half of the northern hemisphere troposphere, the concentration of CO is increased from the present level of about 100 ppbv {parts per billion by volume) to about 300 ppbv. Hydrocarbons Hydrocarbons are an extremely diverse class of organic compounds consisting only of carbon and hydrogen. They include aliphatic hydrocarbons (alkanes) such as methane, ethane, and propane; olefins (alkenes) such as ethylene and propylene; alkynes such as acetylene; and aromatic compounds such as benzene, toluene, and the xylenes. In addition to the hydrocarbons, numerous oxygen-containing compounds such as alcohols, ethers, aldehydes, ketones, and carboxylic acids have been identified in fire emissions. In fact, more than 200 individual compounds have been identified in forest fire emissions, and considering the results of recent studies of cigarette smoke, it is likely that the actual number of compounds emitted is in the many thousands. Figures 6.1 and 6.2 are chromatograms of air collected above slash burning in the tropical forests of Brazil (Greenberg et al., 1984~. These chromatograms illustrate the numerous compounds typically found in fire emissions. Total hydrocarbon emissions have been reported to be in the range of 0.2 to 3.2 percent in laboratory fires and 1.4 to 5.4 percent in a limited number of field fires (McMahon, 1983~. In recent measurements of biomass burning in Brazil (Greenberg et al., 1984), emission factors of 2.0 percent for grassland fires and 2.7 percent (expressed as percent of carbon dioxide by volume) for forest fires were obtained. Methane made up 35 percent of the grassland emissions and 50 percent of the forest emissions. As an estimate for nuclear war fires, the committee has adopted an emission factor of 2 percent (based on weight of fuel burned) for total hydrocarbons and further has assumed that half of these emissions are due to methane, which is relatively less reactive than the higher hydrocarbons. For the baseline scenario, this results in a total emission of 45 Tg of methane and 45 Tg of other hydrocarbons. The methane emission results in an increase in its concentration at mid-latitudes of 70 ppbv. This represents only a minor increase in the ambient methane concentration of 1650 ppbv. As a result, the methane *Unless otherwise noted, all emission factors quoted refer to the mass of a particular chemical species produced per mass of fuel consumed.

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111 a, ax ~ ~ - cN l ~ , . , . - 4 - c Q o Q (~ C) O ( O ~ _ ~ a) Q o Cot m ' a, Z ~ ~ m Len m O ' 0' I a Q C I// ~ ~ _. ULA~' i, I ~ I I I I ~ I I I I I I 0 2 4 6 8 10 12 14 16 18 20 22 24 min FIGURE 6.1 Light hydrocarbon chromatogram of air collected above slash burning in the tropical forests of Brazil (Greenberg et al., 1984~. input may be ignored in the calculations of tropospheric photochemistry. To represent the nonmethane hydrocarbons, the committee has chosen to distribute the emissions as 25 percent ethane, 25 percent propane, and 50 percent ethylene, as these are the major compounds observed in fire emissions, approximately 50 percent of which are alkenes. Oxides of Nitrogen Data for nitrogen oxide emissions in forest and urban fires are still limited. The flame temperatures are generally not high enough in isolated fires to produce nitric oxide directly from air. The fixed nitrogen in the urban and forest fuels represents another fire-produced source of oxides of nitrogen. For example, for ponderosa pine the nitrogen content ranges from 0.1 percent in boles to 1 percent in growing needles (Tangren et al., 1976~. The Environmental Protection Agency has assigned an emission factor of 0.2 percent (as nitrogen dioxide) based on laboratory burning of landscape refuse (McMahon, 1983~. Ward et al. (1982} recently reported a value of 0.18 percent from burning forest materials in a field study. Another study (DeAngelis et al., 1980) found a nitrogen dioxide emission factor of 0.19 percent for the burning of wood in fireplaces. Burning of wood, bark, and limbs at temperatures below 1000C gave an average emission factor of 0.15 percent, compared to 0.75 percent for pine needles and other forest foliage (Clements and McMahon, 1980~. Considering that lumber makes up most of the urban fuels, the committee has adopted a conservative emission factor of 0.15 percent. This results in a total

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112 a' c x I 1 a) C ~Q c I m a, C X c 0 a) a, a) ~m c a, ~ 4 - 0 ~ x G) ~a) X N __, ' 1 1 1 1 1 l I ' I ' I ' I ' I ' I ' I ' I ' I ' I ' I ' I ~ I ' I ~ _ 0 4 8 12 - c ~ O x -. - 16 20 24 28 32 36 40 min FIGURE 6.2 Heavy hydrocarbon chromatogram of air collected above slash burning in the tropical forests of Brazil (Greenberg et al., 1984~. emission to the atmosphere of 6.8 Tg of nitrogen dioxide (equivalent to 4.4 Tg of nitric oxide) from fires for the baseline scenario. EFFECTS OF EMISSIONS Ozone Shield Reduction The first perceived threat of stratospheric ozone by pollutants implicated the oxides of nitrogen (NO and NO2, known collectively as NOX). At that time, the early 1970s, it was the prospect of supersonic flight that caused concern (see, e.g., NRC, 19731. Threats to the ozone layer from emissions of chlorofluorocarbons and from increases in nitrous oxide (N2O) concentrations (caused by the increased application of nitrogen fertilizers) have been recognized and assessed (see, e.g., NRC, 1982~. The problem of ozone reduction by N2O increases is in essence the same as that of reduction by adding NOX, since N2O is converted to NO in the stratosphere. In 1975 the NRC conducted a workshop for the purpose of studying effects of large-scale nuclear detonations. Of all of the aspects addressed, that concerning the effects of NOX injection received the most detailed treatment because of the recent awareness brought about by the SST studies (Crutzen, 1971; Johnston, 1971) and the work of Foley and Ruderman (1973), who pointed out that the NOX produced in the fireballs of nuclear weapons should lead to ozone reduction (see also Johnston et al., 1973~. Recently, estimates have been made of ozone reductions from NOX injections for various nuclear war (Chang and Wuebbles, 1982; Crutzen and Birks, 1982~. all of these studies and their respective scenarios Table 6.1. scenarios The results of are summarized in

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113 The list of chemical reactions thought to describe the behavior of ozone in the stratosphere is long and imposing. The interactions of the various atoms and molecules among themselves and with sunlight and their further dependency upon atmospheric transport make up a very complicated system. Though much is known about this system and the ability to model it has increased considerably in the last decade, much uncertainty still remains attendant to the application of the models to such drastic perturbations as those in the baseline scenario. However, there is now a large body of evidence that concentrations of ozone in the present stratosphere are principally controlled by NOX from natural sources. For this reason alone, it is expected that a large perturbation in the stratospheric burden of NOX, particularly in the upper regions of the stratosphere, would result in a large decrease in the ozone column. The committee attempts here to give only a brief explanation of the manner in which NOX causes ozone reduction in the baseline and excursion cases. (For a thorough review of the chemistry of stratospheric ozone, the reader is referred to Logan et al. (1978~. An update is available in the appendixes by Wofay and Logan and by Anderson in NRC (1982~.) Figure 6.3 shows a "normal" ozone concentration vertical profile and the altitude ranges into which the NOX would be deposited in the 6500-Mt baseline scenario and the 8500-Mt excursion scenario. The ozone concentrations are controlled by balances of production and loss reactions and transport. There are several sets of photochemical reactions, some of which form cycles that can explain much of the observed behavior of ozone. These cycles include catalytic destruction of odd oxygen (O3 and O atoms) by the oxides of nitrogen, the odd hydrogen radicals tHO and HO2), and the chlorine radicals (C1 and C1O). The pertinent cycle for ozone destruction by NOX is the set of reactions: NO + O3 ~ NO2 + O2 NO2 + O ~ NO + O2 O3 + O ~ 2O2 At mid-latitudes in the normal atmosphere, this reaction cycle provides the principal means of odd oxygen destruction above about 23 km. Although the cycle also provides most of the chemical loss of odd oxygen at lower altitudes, the rate of the NO2 + O reaction (which limits the rate of the cycle) slows in relation to the rate of transport as the altitude decreases below about 23 km. The amount of ozone reduction caused by injection of NO into the stratosphere depends on the amounts of NO and their distribution with altitude, which in the case of a nuclear bomb depend upon the yield and height of burst. Figure 4.3 shows the distribution of nuclear cloud tops and bottoms used to calculate the distributions of injected NO in model calculations of ozone reduction. Thus the estimate of the ozone reduction that would result from a nuclear war depends on the yield, type of burst, and latitude, for each weapon of the scenario used. For the baseline scenario, concentrations of NOX would be greatly enhanced in the lower stratosphere up to about 19 km.

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114 nor 50 40 L1J ~ 30 - 20 10 o - - Regions of NOx I ejection Baseline l o O O 0 o Excursion ~ + 1 o 1 1 1 \ 1 1 1 o1 2 O3 DENSITY (cm~3) 1013 FIGURE 6.3 Concentration (solid line) of ozone in the unperturbed atmosphere at regions of NOX injection. The ozone reduction at these elevations would occur because the rate of the catalytic cycle shown above would be enhanced relative to removal by transport. The ozone destruction rate would also increase as the oxides of nitrogen mixed upward, where the ozone concentrations are higher and the photochemical reaction rates are faster. It is a technically noteworthy point that for this massive low-level injection of NOX, below the level of the ozone maximum at 25 km, the overlying ozone would prevent compensating odd oxygen production resulting from photolysis of O2 at the lower elevations. The Lawrence Livermore National Laboratory (LLNL) one-dimensional eddy diffusion and chemical reaction model was used to estimate the amounts of ozone reduction with time corresponding to the present two scenarios (J.E. Penner and P.S. Connell, Lawrence Livermore National Laboratory, private communication, 1984~. The results are shown in Figure 6.4, which illustrates that for the baseline case the maximum ozone reduction of 17 percent (average over the northern hemisphere) would be reached 1 year after the war and recovery to one-half of the peak reduction would require an additional 2 years. The relatively slow development of the ozone minimum reflects primarily the slow upward transport of NOX to regions where the odd oxygen destruction rates are greater. The 8500-Mt excursion scenario would place additional large amounts of NOX at elevations up to about 37 km due to the use of much larger

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115 ~ -10 ~ LL \ / I -20 ~ ~ 1 ~ o -30 ~ / ~ / Z \ / O E / O ~40 \ / , _ ~ 0 2 -20 -40 -50 Computed Hemispheric Average Ozone Column Change as a Function of Time B = Baseline Scenario (6500 Mt.) E = Excursion Scenario (Baseline plus 100 x 20 Mt) 1 1 1 1 1 1 1 1 4 6 8 10 TIM E (yr) FIGURE 6.4 Hemispherically averaged percent ozone depletion estimated in a one-dimensional eddy diffusion and chemical reaction model (J.E. Penner and P.S. Connell, LLNL, private communication, 1984~. weapons. This would cause very rapid reduction of ozone in the region where its concentrations are the highest. This is reflected in the shorter time to achieve maximum reduction, namely about 8 months to reach 43 percent reduction. Recovery to one-half that value would occur after 4 years. The complex set of chemical reactions that control stratospheric ozone concentrations constitutes a system in which the dependency of ozone reductions amounts on NO injection amounts is somewhat nonlinear. These effects were discussed in the NRC (1975) report (see particularly Figure 1.9~. Though there are differences in details between the model used then and the present model, the plot is still approximately applicable to the present model for the purpose of rough guidance. The results of this study are consistent with those of other studies using the LLNL model. Comparison of these results with those reported by Chang and Wuebbles (1982) shows the same shapes for the ozone versus time curves. Table 6.1 presents a comparison of the present scenarios, NOx injections, and maximum ozone (03) reductions with those of Chang and Wuebbles and of the Ambio scenario. The details of time to maximum reduction, the value of maximum ozone reduction, and time to recover to one-half the maximum depletion are scenario-dependent. That is, the amount and distribution of NOx and thus the model-derived details depend on the numbers and yields of individual weapons. (The results for the excursion scenario are

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116 somewhat similar to those reported in NRC (1975~. However, there are substantial differences in several of the reaction rate parameters as well as yields and numbers of weapons.) The Ambio scenario gave no ozone reduction and is consistent with the results of the present study for the reason that the preponderance of the NO was injected below 12-km altitude. There the ozone destruction by the NOx cycle is offset by the creation of ozone by the smog cycle (see next section). The calculated ozone changes discussed above were obtained with the use of models in which the stratospheric transport properties are those that represent the present (unperturbed) atmosphere. The perturbation of the atmosphere by smoke and dust could affect the circulation of the stratosphere and thus provide a circumstance different from that upon which the present ozone calculations were based. As discussed in Chapter 7, the committee has no sound qualitative notions as to how stratospheric circulation would be altered. In the absence of further information, the committee believes that the use of the unperturbed atmospheric transport characteristics provides the best basis for assessing the ozone reductions caused by NO injections from nuclear bursts. Since the model used in this study considers transport only in the vertical dimension, it cannot provide an estimate of the amounts of NOx transported into the southern hemisphere. The ability of the atmosphere to transport trace substances across the equator in the stratosphere was demonstrated by many observations of radioactive debris from nuclear weapons testing in the atmosphere. The nature of this phenomenon was delineated by Mahlman and Moxim (1978) using a general circulation model. Their study, using a single mid-latitude tracer injection, showed that the maximum burden in the southern hemisphere occurred about 9 months after the injection and was less than 10 percent of the initial amount injected. Crutzen and Birks (1982) calculated southern hemisphere ozone reduction to be of the order Of 15 percent occurring after the injection of somewhat higher amounts of NOx than in the excursion case. Ozone Holes and Effects of NO2 Radiation Absorption Luther (1983) has studied short-term chemical and radiative effects of injections of NO into the stratosphere by nuclear weapons. The particular problem he addresses is the Ozone hole." Rapid heating of portions of the stratosphere containing high concentrations of NO2, with subsequent mixing throughout the heated and destabilized volume, causes the ozone hole, which is a large reduction in the ozone column abundance distributed over most of the vertical extent of the stratosphere, but confined laterally. Ozone holes would permit a very large increase in irradiance of ultraviolet light at the top of the troposphere, which, in the absence of smoke or clouds, would result in life-damaging effects at the surface. Luther's study assumed that the cloud remained cylindrical throughout the depths of the stratosphere and that horizontal mixing could be represented by eddy diffusion.

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117 These assumptions are probably not realistic, since the "fillings of the holes by shear in the vertical is likely to be rapid and effective. Thus, it is considered that the ozone holes would exist for no more than a few hours and their effects would be less severe than those from global-scale reduction. Effects on Ozone calf Past Nuclear Weapons Tests In accordance with the committee's estimates, the approximately 300 Mt of total bomb yield in multimegaton atmospheric bursts by the United States and USSR in 1961 and 1962 introduced about 3 x 1034 additional molecules of nitric oxide into the stratosphere. Thus one might ask whether these tests resulted in a depletion of the ozone layer. Using a one-dimensional model, Chang et al. (1979) estimated that these nuclear weapons tests should have resulted in a maximum ozone column depletion in the northern hemisphere of about 4 percent in 1963. Analysis of the ground ozone observational data by Johnston et al. (1973) showed a decrease of 2.2 percent for the period 1960-1962 followed by an increase of 4.4 percent in 1963-1970. Although these data are consistent with the magnitude of the ozone depletion expected, by no means is a cause and effect relationship established. Angell and Kor shover (1973) attribute these observed ozone column changes to meteorological factors. The ozone decrease began before most of the large weapons had been detonated and persisted for too long a period to be totally attributed to recovery from bomb-induced ozone depletion. Unfortunately, because of the large scatter in the ground-based ozone observational data and our lack of understanding of all of the natural causes of ozone fluctuations, one cannot draw definite conclusions about the effects of nuclear explosions on stratospheric ozone on the basis of previous tests of nuclear weapons in the atmosphere. Uncertainty in Model Results Normally, a scientific study using a model to "predict" a result should be accompanied by an analysis of uncertainties ending with a set of error limits on that result. The assessment of global effects of perturbing trace substances on stratospheric ozone has caused much effort to be expended in attempting to estimate error limits on calculated ozone reductions. Yet after more that a decade of experience in this exercise the most recent assessment by the NRC (1984a) states, The detailed treatments often leave the wrong impression that the actual sources of uncertainty are well defined. . . . [O] nly a qualitative statement of uncertainty is made here. n The perturbation of the stratosphere by NO and smoke emissions from a large-scale nuclear war is likely to be so large that effects not considered could well play an important role. Certainly, the models used in the present assessment were not constructed to handle such perturbations. Further, the present problem is complicated by the many injections of NO in the vicinity of the tropopause by low-yield

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118 weapons. The estimated ozone depletion for the baseline case is quite sensitive to the height of the tropopause relevant to the particular bursts. As discussed in Chapter 4, there is uncertainty associated with the estimates of cloud tops and bottoms. All of these factors combine to make of any rational estimate of error limits in ozone reduction a virtual impossibility. The numbers calculated here, though given to two figures, should be viewed as plausible values that are based upon the best methods available to the committee. Tropospheric Composition Changes Because the troposphere is in direct contact with the biosphere, it is especially important to understand the chemical changes that would take place in this region of the atmosphere following a nuclear war. The many fires ignited by the nuclear explosions would inject large quantities of carbon monoxide, hydrocarbons, and many other organic compounds into the atmosphere. Both fires and the nuclear explosions themselves would produce large quantities of oxides of nitrogen. In the presence of sunlight, these compounds react to form strong oxidants, particularly ozone and organic peroxides such as peroxyacetyl nitrate (PAN). PAN and related compounds have strong phytotoxic effects. Ozone, while being necessary in the stratosphere to serve as a shield against solar ultraviolet radiation, is considered undesirable at ground level because of its toxic effects on both plants and animals. Whether or not a dense photochemical smog with high oxidant concentrations would form in the wake of a nuclear war is difficult to evaluate for several reasons. Perhaps the largest uncertainties are associated with (1) the extent and duration of the darkening caused by the smoke and dust, and (2) changes in tropospheric dynamics and precipitation rates, which in turn affect the lifetimes of the relevant chemical species. The generalized mechanism of photochemical smog formation includes the critical reaction sequence ROO + NO ~ NO2 + RO NO2 + he ~ NO + O O + O2 + M ~ O3 + M where R can be a hydrogen atom or any organic radical and M is any molecule. This sequence of reactions requires sunlight (photon, ho) and oxides of nitrogen (NO and NO27. Sunlight is also necessary to the formation of the hydroxyl radical, OH, as follows, O3 + he ~ O2 + O(1D2) O(1D2) + H2O ~ 2 OH where 0~1D2) is an electronically excited oxygen atom. The OH radical is an important initiator of chain reactions in the atmosphere via reactions such as CO ~ OH ~ CO2 + H

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119 followed by H + O2 + M ~ HOO + M and RH + OH ~ H2O + R which is followed by R + O2 + M ~ ROO + M J.E. Penner and P.S. Connell (Lawrence Livermore National Laboratory, private communication, 1983) have investigated the tropospheric composition changes associated with the baseline scenario using a one-dimensional model of tropospheric photochemistry. Because most of the oxides of nitrogen in the troposphere are removed in this model by natural processes of dry deposition and rainout during the first few weeks, while the sunlight is greatly attenuated by suspended smoke and dust, the average concentration of ozone in the troposphere increases by less than a factor of 2. After several more weeks, the ozone concentration is expected to have decreased to near-ambient levels as the many chemical pollutants are removed from the atmosphere. The high loading of particulate matter in the troposphere may be significant not only in blocking sunlight, but also in promoting heterogeneous reactions. Assuming all smoke particles are perfect spheres of radius 0.05 um with a density of 1 g/cm3, the specific surface area is 60 m2/g. If the 200 Tg of smoke aerosol of the baseline case is uniformly distributed with a constant mixing ratio (aerosol particles/molecules of air), then every atmospheric molecule collides with a particle on the average about 4 times every second. This collision lifetime is shorter that the lifetime of many highly reactive atmospheric species. Birks and Staehelin (1984) have investigated the possible role of reactions on particulate surfaces in further reducing tropospheric oxidant concentrations. They found for the baseline case that oxidant formation in the troposphere is significantly inhibited when the efficiencies (y) of reaction upon collision with aerosol surfaces exceed 10-6 for O3, 10~1 for OH and/or 10-2 for HO2. The variations in values of y that result in significant reduction in oxidant formation simply reflect the relative lifetimes of oxidant species in the atmosphere. Whereas a small value of To is required for ozone, a relatively long-lived species, a value Of YoH > 10-1 is required for hydroxyl radicals, which have a very short atmospheric lifetime. The reaction efficiencies for atmospheric species with smoke aerosol have not been measured. However, the reaction of OH, one of the most important oxidants in the atmosphere, with a graphite surface has been studied (Mulcahy and Young, 19751. Because the rate of the reaction was sufficiently fast to be diffusion limited in the experimental apparatus, only a lower limit for YOH of 5 x 10-2 was obtained. Although Mall effects" for other labile atmospheric species such as O3, O. and HO2 are well known because of the

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120 difficulties they pose in measurements of their homogeneous reaction rates, no ~ values for reactions with atmospheric aerosol have been obtained. It is not possible to make quantitative predictions of all the chemical composition changes of the troposphere following a nuclear war. However, it seems likely that the rate of oxidation of tropospheric species would be greatly decreased, particularly near the surface of the earth, for the period of time that the particulate matter resides in the atmosphere. Although oxidants in the atmosphere are usually looked upon as undesirable because of the damage they cause to plants and animals, oxidants serve an important function in cleansing the atmosphere of many anthropogenic and biogenic In fact, the lifetimes of nearly all compounds released to the atmosphere are determined by the rates of reaction with the hydroxyl . -". ~ emlss cons . radical. The source of OH radicals in the troposphere is photolysis of ozone, as discussed above. In addition to the reduced sunlight and loss of OH on particulate surfaces, OH concentrations would be reduced by combination with NO2 to form nitric acid: OH + NO2 ~ M ~ HNO3 + M In addition to the increased burden of toxic chemicals as the result nuclear war fires, one would expect large increases in the concentrations of many reduced compounds for two reasons: (1) the lifetimes of many compounds would be increased by large factors due to reduced concentrations of OH and other oxidants, and (2) biogenic emissions of some compounds might increase by large factors following a nuclear war. For example, compounds such as hydrogen sulfide and dimethyl sulfide are thought to have large biogenic emissions estimated at about 50 To S of each Her vear (Adams et al. 1981: Andreas and Raemdonck, 19831. However, their atmospheric concentrations are limited by short lifetimes of one or two days owing to reactions with the OH radical (Hatakeyama and Akimoto, 1983~. It is difficult to predict the changes in biogenic emission rates that would follow a r.~1 ~' ~' rnh~ e - ~^C!C,~= ~ ~ he '~' arm ~ he lo; ~=r~h^~^ ; ^~1 ''A; r`^ a 1lU~ ~ ="L W"L -l-1l" O~L=~=e. V, bile W"L ~1 ~= ~V=~ICL=' .11~ ~ U" Ally long period of darkness and freezing temperatures, would be expected to result in the death of many plants and animals, which in turn might lead to an increase in the rate of release of many reduced compounds. On the other hand, the low temperatures over land surfaces could decrease the rate of bacterial degradation of organic matter, and frozen freshwater systems could delay the escape of gaseous compounds to the atmosphere. Because of the large heat capacity of the mixed layer of the ocean, the temperature of the ocean would be little changed. The principal effect of a nuclear war on biogenic emissions from the ocean would probably result from periods of low light intensity. Photosynthesis in the ocean takes place to a critical depth where the sunlight is attenuated to about 1 percent of its normal incident light flux. The darkness following a nuclear war would shift this critical depth much closer to the surface. As a result, one might expect the death of a

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121 . significant fraction of the phytoplankton and zooplankton of the northern hemisphere ocean following a nuclear war (Milne and McKay, 1982). Despite the large uncertainties, it is possible to place reasonable bounds on the concentrations of reduced sulfur compounds that would accumulate in the atmosphere. As a result of the rapid oxidation rate of dimethyl sulfide (DMS) in the normal atmosphere, the concentration of DMS in marine air is at least 2 orders of magnitude below the concentration that would be in equilibrium with seawater (Andreas and Raemdonck, 1983~. As an upper bound, we may assume that the atmospheric concentration of DMS comes into equilibrium with surface water, resulting in an atmospheric mixing ratio of 21 ppbv. As a lower bound, we assume release of DMS at the present average sea-to-air flux (290 ug S/m2 per day) for a period of 1 month ~ mixing to an altitude of 10 km. This results in a mixing ratio of 0.8 ppbv. Considering that biogenic emissions of hydrogen sulfide are comparable in magnitude to DMS and that there would also be emissions from dimethyl disulfide and methyl mercaptan, for which emission factors are not well known, it appears likely that following nuclear war, the total concentration of reduced sulfur compounds in the troposphere would accumulate to a few parts-per-billion by volume. Although these are not toxic levels, at least for short-term exposure to humans, it is noteworthy that the threshold for smell in humans has been found to be in the ranges 0.9 to 8.5 ppbv for H2S and 0.1 to 3.6 ppbv for (CHRIS. _ _ ~ _ ~ and allow uniform Toxic Chemical Releases In addition to the emissions of carbon monoxide, nitrogen oxides, and organic compounds produced by the pyrolysis and partial combustion of wood, several million tons of noxious chemicals would be released to the atmosphere as a result of the pyrolysis and partial combustion of synthetic polymers such as rubber, plastics, and synthetic fibers located in urban areas, and chemicals in industrial storage. These chemical releases could have severe local consequences in and near the heavily populated urban areas. Occasional accidental releases of noxious chemicals have resulted in temporary evacuations of large areas. Contamination of the ground at very low levels (one part per million and below) by some particularly toxic chemicals has caused the permanent evacuation of some areas (e.g., Love Canal, New York, and Times Beach, Missouri). Recent attention has been drawn particularly to the polychlorinated biphenyls (PCBs), dioxins, and chlorine- substituted dibenzofurans. In the United States alone, more than 300,000 tons of PCBs are in use in electrical equipment and approximately 10,000 tons in storage (S. Miller, 1983~. A large fraction of this toxic chemical could be released to the environment in a nuclear war. Apparently, dioxins and dibenzofurans may be produced in large quantities in the combustion of fuels containing chlorine, although this is currently a matter of considerable controversy (J.A. Miller, 1979; Bumb et al., 1980; Chemical and Engineering News, 1983~.

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122 Annual production in chemicals is provided in percent of these amounts the United States of some important industrial Table 6.2. On the average, perhaps 5 to 10 are in storage at any particular time. Pyrolysis and partial combustion of these and less abundant chemicals would result in the deposition of thousands of chemical species in the atmosphere and ultimately in the soil and water. The chlorine compounds would be expected to account for a large fraction of the more toxic, mutagenic, teratogenic, and carcinogenic compounds. The problem of toxic chemicals released in a nuclear war is highly specific to locality and does not lend itself readily to general analysis. It seems likely, however, that portions of most of the urban areas affected would be seriously contaminated, at least in the smoky air during and immediately following burning. The possibility of serious local contamination of the ground and water for long times after the war cannot be ruled out. Among the toxic materials released to the environment would be asbestos. The current world production of asbestos fibers amounts to about 4 million metric tons per year. More than 30 million tons (30 Tg) of asbestos has been accumulated in the United States alone. Accumulation by industrialized nations is in excess of 100 Tg. These fibers are bound in a wide variety of construction materials and other products. Much asbestos contained in the nonflammable materials would be released as the result of pulverization by the nuclear blast. Since asbestos fibers are nonflammable, they would also be released to the atmosphere upon combustion of materials such as floor tile and asphalt shingles. It is difficult to estimate how much asbestos would be released to the atmosphere as the result of a nuclear war. However, when mixed uniformly throughout the lower 9 km of the atmosphere and over half of the northern hemisphere, the atmospheric concentration of asbestos is calculated to be about 0.3 fibers per cubic centimeter for each teragram of asbestos released. This calculation uses the conversion factor used in epidemiological studies in which it is assumed that 1 fiber would be detected by phase contrast light microscopy for every 30 x 10-12 g of suspended asbestos. An optical fiber is defined as any particle longer than 5 Em, having a length-to-diameter ratio of at least 3-to-1 and a maximum diameter of 5 um. Of course, the actual number of fibers is much larger, owing to the preponderance of smaller fibers not counted. The present Occupational Safety and Health Administration (OSHA) standard for exposure to asbestos is a time-weighted average of 2.0 fibers per cubic centimeter over an 8-h period, and OSHA announced a decision to lower it to 0.5 fiber per cubic centimeter in November 1983. A recent NRC study (NRC, 1984b) estimated the average nonoccupational exposure in the United States to asbestos to be 0.0004 fibers per cubic centimeter. Five teragrams (less than 5 percent of the world accumulation) of asbestos released to the atmosphere would increase the general population exposure to asbestos by a factor of about 4000 for the period of time that the particles are suspended and uniformly distributed. Of course, the fibers would be subject to resuspension and would be concentrated in the boundary layer of the atmosphere.

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123 TABLE 6.2 U.S. Production of Some Major Chemicals in 1982 Millions of Tons Sulfuric acid Ammonia Ethylene Chlorine Phosphoric acid Toluene Nitric acid Propylene Ethylene dichloride Xylenes Benzene Methanol Ethylbenzene Vinyl chloride Styrene Hydrochloric acid Terephthalic acid Ethylene oxide Ethylene glycol Acetic acid Cumene Phenol Acrylonitrile Vinyl acetate Butadiene Acetone Formaldehyde Propylene oxide Isopropanol Cyclohexane Adipic acid Acetic anhydride Ethanol 29~4 14~1 11~2 8~3 7~8 6~9 6~9 5~6 4e5 3~8 3~6 3~3 3~0 3~0 2~7 2~4 2~3 2~2 1~8 1~2 1~2 0~96 0~92 0~85 0~83 0~80 0~76 0~67 0~59 0~58 0~54 0~48 0~46 REFERENCES Adams, D.F., S.O. Farwell, E. Robinson, M.R. Pack, and W.L. Bamesberger (1981) Biogenic sulfur source strengths. Environ. Sci Technol. 15:493-498. Andreas, M.O., and H. Raemdonck (1983) Dimethyl sulfide in the surface ocean and the marine atmosphere: A global view. Science 221:744-747. , .

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124 Ambio (1982) Nuclear war: The aftermath. 11~2/3~:75-176. Angell, J.K., and J. Ror shover (1973) Quasi-biennial and long-term fluctuation in total ozones. Mon. Weather Rev. 101:426, 104:63. Birks, J.W., and J. Staehelin {1984) Changes in tropospheric composition and chemistry resulting from a nuclear war. Draft - manuscript. Bumb, R.R., W.B. Crummett, S.S. Cutie, J.R. Gledhill, R.H. Hummel, R.O. Ragel, L.L. Lamparski, E.V. Luoma, D.L. Miller, T.J. Nestrick, L.A. Shadoff, R.H. Stehl, and J.S. Woods (1980) Trace chemistries of fire: A source of chlorinated dioxins. Science 210:385-389. Chang, J.S., and D.J. Wuebbles (1982) The Consequences of Nuclear War on the Global Environment. Hearing before the Subcommittee on Investigations and Oversight of the Committee on Science and Technology, U.S. House of Representatives, Sept. 15. Chang, J.S., W.H. Duewer, and D.J. Wuebbles (1979) The atmospheric nuclear test of the 1950's and 1960's: A possible test of ozone depletion theories. J. Geophys. Res. 84:1755. Chemical and Engineering News (1983) Special Issue on Dioxin. June 6. Chi, C.T., et al. (1979) Source Assessment: Prescribed Burning, State of the Art. EPA Report EPA-600/2-79-019h. Research Triangle Park, N.C.: U.S. Environmental Protection Agency. Clements, H.B., and C.K. McMahon (1980) Nitrogen oxides from burning forest fuels examined by thermogravimetry and evolved gas analysis. Thermochim. Acta 35:133. Crutzen, P.J. (1971) Ozone production rate in an oxygen-hydrogen oxide atmosphere. J. Geophys. Res. 76:7311. Crutzen, P.J., and J.W. Birks (1982) The atmosphere after a nuclear war: Twilight at noon. Ambio 11:114-125. DeAngelis, D.G, D.S. Ruffin, and R.B. Reznik (1980) Preliminary Characterization of Emissions from Wood-fired Residential Combustion Equipment. EPA Report 600/7-80-040. Research Triangle Park, N.C.: U.S. Environmental Protection Agency. Foley, H.M., and M.A. Ruderman (1973) Stratospheric NO production from past nuclear explosions. J. Geophys. Res. 78: 4441. Gilmore, F.R. (1975) The production of nitrogen oxides by low-altitude nuclear explosions. J. Geophys. Res. 80 :4553. Greenberg, J.P., P.R. Zimmerman, L. Heidt, and W. Pollack (1984) Hydrocarbon emissions from biomass burning in Brazil. J. Geophys. Res. 89: 1350-1354. Hatakeyama, S., and H. Akimoto (1983) Reactions of OH radicals with methanethiol, dimethyl sulfide, and dimethyl disulfide in air. J. Phys. Chem. 87: 2387-2395. Johnston, H.S. (1971) Reduction of stratospheric ozone by nitrogen oxide catalysts from supersonic transport exhaust. Science 173:517. Johnston, H.S., G. Whitten, and J.W. Birks (1973) Effects of nuclear explosions on stratospheric nitric oxide and ozone. J. Geophys. Res. 78:6107. Logan, J.A., M.J. Prather, S.C. Wofsy, and M.B. McElroy (1978) Atmospheric chemistry: Response to human influence. Phil. Trans. Roy. Soc. London 290:187.

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125 Luther, F.M. (1983) Nuclear war: Short-term chemical and radioactive effects of stratospheric injections. Paper presented at the International Seminar on Nuclear War, 3rd Session: The Technical Basis for Peace. Ettore Majorana Centre for Scientific Culture, Erice, Sicily, August 19-24, 1983. Mahlman, J.D., and W.J. Moxim (1978) Tracer simulations using a global circulation model: Results from a mid-latitude instantaneous source experiment. J. Atmos. Sci. 35:1340-1374. McMahon, C.K. (1983) Characterization of forest fuels, fires, and emissions. Paper presented at the 76th Annual Meeting, Air Pollution Control Association, Atlanta, Ga. Miller, J.A. (1979) Chemists disagree on dioxin sources. New Sci. (Oct. 4~:25. Miller, S. (1983) The PCB imbroglio. Environ. Sci . Technol. 17:1LA-14A. Milne, D.H., and C.P. McKay (1982) Response of marine plankton communities to a global atmospheric darkening. Geol. Soc. Am. Spec. Pap. 190:297-303. Mulcahy, M.F.R., and B.C. Young (1975) Heterogeneous reactions of OH radical. Int. J. Chem. Kinet. 7(suppl.~:595-609. National Research Council (1973) Climatic Effects of Supersonic Flight. Washington, D.C.: National Academy of Sciences. National Research Council (1975) Long-Term Worldwide Effects of Multiple Nuclear Weapon Detonations. Washington, D.C.: National Ac. emy of Sciences. National Research Council (1982) Causes and Effects of Stratospheric Ozone Reduction: An Update. Washington, D.C.: National Academy Press. National Research Council (1984a) Causes and Effects of Changes in Stratospheric Ozone: Update 1983. Washington, D.C.: National Academy Press. National Research Council (1984b) Asbestiform Fibers: Nonoccupational Health Risks. Washington, D.C.: National Academy Press. Ogren, J.A. (1982) Deposition of particulate elemental carbon from the atmosphere. Pages 370-391 In Particulate Carbon: Atmospheric Life Cycle, edited by G.T. Wolff and R.L. Klimisch. New York: Plenum Press. Ryan, P.W., and C.K. McMahon (1976) Some chemical and physical characteristics of emissions from forest fires. Paper 76-2.3 presented at the 69th Annual Meeting, Air Pollution Control Association, Portland, Ore. Sandberg, D.V., S.G. Pickford, and E.F. Darley (1975) Emissions from slash burning and the influence of flame retardant chemicals. J. Air Pollut. Control Assoc. 25:278-281. Sedlacek, W.A., E.J. Mroz, A.L. Lazrus, and B.W. Gandrud (1983) Various Nitric Acid Concentrations in the Lower Stratosphere: 1971-1982. Report LA-UR-83-3138. Los Alamos, N.Mex.: Los Alamos National Laboratory. Tangren, C.D., C.K. McMahon, and P.W. Ryan (1976) Contents and effects of forest fire smoke. Southern Forestry Smoke Management Guidebook. U.S. For. Serv. Gen. Tech. Rep. SE-10.

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126 Tur co, R.P., O.B. Toon, T.P. Ackerman, J.B. Pollack, and C. Sagan (1983) Global Atmospheric Consequences of Nuclear War. Interim Report. Marina del Rey, Calif.: RED Associates. 144 pp. Ward, E.E., et al. (1982) Measurement of smoke from two prescribed fires in the Pacific Northwest. Paper 82-8,4 presented at the 75th Annual Meeting, Air Pollution Control Association, New Orleans, La .