Report from the spring ACS meeting Three symposia at the A C S meeting in Seattle were devoted to the environmental chemistry related to current environmental problems. They were • the ozone layer, • cloud chemistry, and • organic emissions from combustion processes. This report describes these symposia; general papers are not discussed. The ozone layer In 1974, scientists F. Sherwood Rowland and Mario J.. Molina hypothesized that chlorofluorocarbons migrate slowly into the stratosphere where—through multiple, complex chemical reactions—they react and thereby destroy ozone. The presence of ozone in the stratosphere serves to reduce the amount of ultraviolet radiation reaching the earth's surface and thereby protects us from skin cancer and other harmful effects, such as reduced agricultural and marine productivity. The big question: Has any harm to the ozone layer been documented? The answer is not straightforward. According to " T h e World Environment 1972-1982," a report by the United Nations Environment Programme ( U N E P ) , the depletion of ozone postulated early in the decade, as a result of supersonic transport and increasing releases into the stratosphere of chlorofluorocarbons from such sources as spray cans and refrigerators, was undetectable by current methods. There was, therefore, uncertainty over whether or not the destruction process was occurring and whether its predicted environmental consequences, one of which was an increase in human skin cancers, were likely. Scientific uncertainty remains today, because depletion figures are based solely on mathematical models. For example, the model used by the U N E P calculated that a total ozone depletion of about 1% should have al0013-936X/83/0916-0241A$01.50/0
Seattle, Wash. For the spring ACS meeting, March 20-25, the weather was sunny, warm, and definitely atypical. ready occurred, but such a small change could not be detected directly with the technology available at the time, as it was well within the range of natural variation. The general reason for the timeto-time change in the sign of the ozone effect is readily given. Ozone is slowly photochemically produced by the m e t h a n e - H O x - N O x - s m o g reactions in the troposphere and in parts of the lower stratosphere. Then ozone is catalytically destroyed by N O * in the middle stratosphere. The net N O * effect on the vertical column of ozone is the difference between the ozone destruction at high altitudes and ozone generation at low altitudes. On the other hand, some measurements are not yet possible. For technical reasons it has not been possible to measure the concentration of H O and H O O in the 15-130-km altitude range. These chemical species are associated with destruction processes. The A C S Award for Creative Ad-
© 1983 American Chemical Society
vances in Environmental Science & Technology was presented to F. Sherwood Rowland at the awards banquet on Monday evening. On Tuesday, at a symposium in his honor, Rowland talked about the five most abundant organochlorine compounds in the troposphere. How did Rowland get into the ozone layer effects study? In 1972, he went to a meeting and heard a paper by Jim Lovelock, who reported measurements of the atmosphere taken aboard ship in South America. In all of his samples, CCI3F was present. Rowland posed the question of whether it is possible to figure out what is going to happen to a molecule like CCI3F when it is released into the atmosphere. Once the material is in the atmosphere there are three ways to remove it: by chemical reaction, rainout, and photolysis. At the symposium Rowland discussed the five most abundant organochlorine compounds in the troposphere in 1983—dichlorodifluoromethane, trichlorofluoEnviron. Sci. Technol., Vol. 17, No. 6, 1983
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romethane, carbon tetrachloride, methyl chloroform, and methyl chlo ride—each of which is present at levels of 350-700 ppt. Of the five, methyl chloride is formed mostly by natural processes; the other four are essentially anthropogenic in origin. Despite an intensive search during the past decade, no important tropospheric removal process has been identified for CC1 4 , CC1 3 F, or CC1 2 F 2 , except upward diffusion into the stratosphere. In the 10-year period from 1970 to 1980, the concentration of organochlorine compounds in the troposphere increased from 1.5 ppb to 3.0 ppb, Rowland said. He believes that some changes are going on in the stratosphere, but that they are not completely explained at the present time. The primary decomposition mech anism in the stratosphere for these three compounds is direct solar pho tolysis by ultraviolet radiation in the 185-230-nm wavelength range. The net effect of the reaction in the stratosphere is the conversion of two molecules of "odd" oxygen into the stable 0 2 form, and hence destruction of ozone. CI + 0 3 — CIO + 0 2 CIO + Ο - * Cl + 0 2 This chain reaction is especially ef fective at altitudes above 30 km be cause of the higher concentration of Ο atoms at these higher altitudes. In addition, there are removal processes. The individual chlorine atoms diffuse upward and downward in the strato sphere in various chemical forms and are eventually removed from the at mosphere as HC1 by rainout in the troposphere. The second symposium speaker, Harold S. Johnston of the University of California at Berkeley talked about the natural ozone balance. Ozone is produced in the stratosphere primarily by the photolysis of oxygen by solar radiation of wavelengths between 180 and 220 nm. In the late 1950s and early 1960s, direct rate measurements were made for the reactions: 0 + 02 + M ^ 0
3
+ M
Ο + 0 3 —· 2 0 2 In 1969, the infrared spectrum of nitric acid was detected during a balloon flight in the stratosphere. By the late 1970s there were numerous balloon flights from several parts of the world that gave N 2 0 vertical profiles from 0 to 35 km. In 1982, N 2 0 measurements from a satellite became available for the first time. 242A
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Balloon flights. Instruments aboard such flights have identified and measured trace gases in the atmosphere. The rate of ozone destruction by the primary N O x catalytic cycle is twice the rate of the reaction Ο + N 0 2 — 0 2 + NO which is 2 k [ N 0 2 ] [O]. Since 1974 at Lawrence Livermore National Labo ratory, models for calculating pertur bations of ozone—by injected N O * in this case—have been repeated for each major revision of rate constraints. Calculations also have been made for each newly recognized important species, for example, chlorine in 1975 a n d H O O N 0 2 i n 1980. Mario J. Molina of the Jet Propul sion Laboratory said that the reactions of hydroxyl radicals with nitric acid and hydrogen chloride play very sig nificant roles in the chemistry of the stratosphere. In particular, the effect of pressure on the rate of these reac tions is not well established. Using a flash photolysis technique coupled to resonance absorption detection, Mario and L. T. Molina have measured the rate constants k] and k 2 for these re actions of the O H radicals in smog chamber studies. For the O H + HNO3 reaction, the reaction rate increases with pressure. A negative temperature dependence and this pressure depen dence support a reaction mechanism that proceeds through an intermediate complex H 2 N 0 4 , which can be stabi lized by collision. For the O H + HC1 reaction, using their resonance fluo rescence apparatus, these investigators have not observed any significant pressure effect at room temperature. Richard S. Stolarski of the N A S A Goddard Space Flight Center in Greenbelt, Md., said that predictions of change in the ozone layer in re
sponse to perturbations, both natural and human induced, are made with mathematical models, incorporating a specific chemical mechanism. The mechanism is the set of reactions con trolling ozone production and loss. This set of reactions is constructed through knowledge gained from mea surements of reaction-rate coefficients in the laboratory. One problem with atmospheric ozone photochemistry is finding a way to test the validity and completeness of the mechanism that has been developed. The mechanism for determining the ozone concentration in the atmosphere consists of its production by ultraviolet solar radiation, which dissociates ox ygen, and its destruction by catalytic processes with nitrogen, hydrogen, and chlorine oxides, along with direct oxygen reactions. Pure oxygen reac tions and N O * reactions show a strong temperature dependence, whereas H O j and chlorine reactions show a relatively weak temperature depen dence. This theory was tested previ ously with satellite temperature and ozone data during disturbed winter weather conditions near 50 km alti tude. The tests demonstrated a de pendence falling between the expected dependence for HOx and N O x , which are presumed to be the predominant loss mechanisms. In conclusion, it is hoped that these calculations will re veal new and better ways of testing the mechanisms in photochemical models of the atmosphere. Ralph J. Cicerone of the National Center for Atmospheric Research ( N C A R ) said that methane may be contributing to the global warming. Atmospheric methane content is sup plied mostly (80-90%) by biological rather than fossil fuel sources. Direct evidence is available on the identity and sizes of the biogenic sources, and the data base is growing. One large source is said to be the activity of ter mites, but there is scientific contro versy about the extent of this contri bution. Another explanation for the increase in atmospheric methane levels includes expansion of the cattle popu lation and increased irrigation in worldwide rice agriculture. The global sources of atmospheric methane and N 2 0 are receiving more attention re cently, partly because their atmo spheric concentrations are increasing globally. Approximately four billion metric tons of methane are now in the atmosphere. From photochemical models of the atmosphere, Cicerone calculates that about 400 million metric tons of methane are destroyed each year, mostly by reaction with
gaseous O H radicals in the lower at mosphere. There is a potential for global climate warming because of increased concentrations of polyatomic gases that absorb 8-13-μπι radiation. In addition to Cicerone's study, re search on the contribution of trace gases in the atmosphere to global warming is underway in many other laboratories around the world. Clouds, clouds William E. Wilson, an E P A em ployee, at Research Triangle Park, N.C., and a former member of the ES& Τ advisory board, was chairman of the symposium on cloud chemistry. In his introduction, he mentioned that the subject of the kinetics of atmo spheric reactions is receiving consid erable attention. Scientists need to determine the order .of reaction for the conversion of sulfur(IV) as SO2 to sulfur(VI) as SC»4~, before any meaningful policy for control of acid rain can be implemented, according to Wilson. If the reaction is zero order, the rate of conversion is independent of SO2 content in the air. If, however, the reaction is first order, it is dependent on the SO2 content in the atmo sphere. Peter V. Hobbs of the University of Washington, Seattle, said that there are four mechanisms by which the acid becomes incorporated into the rain: • nucleation scavenging—the con densation of water vapor onto atmo spheric aerosols, • gas scavenging—the absorption of gases into cloud and precipitation particles, • in-situ production—chemical reaction within cloud and precipitation particles, and • particle scavenging—scavenging of atmospheric aerosol by cloud and precipitation particles. Hobbs said that most work has centered on nucleation scavenging, the first process, which is fairly well un derstood. It is responsible for the initial formation of cloud droplets. The de gree of gas scavenging may be evalu ated, provided either Henry's law is applicable or data are available on the absorption rate into aqueous solution. Hobbs said that for a heavily in dustrialized area, in-situ production of sulfate dominates, while for a remote, clean area, near the ocean, nucleation scavenging is the most important pathway for acidification. In the case of sulfur, acidity produced by gas scavenging alone is unimportant. Model calculations also indicate that large variations in certain parameters of cloud physics—for example cloud
Clouds. Scientists need to know the ki netics of atmospheric reactions before es tablishing any meaningful policy to con trol acid rain. liquid water content or ice crystal concentrations—can increase the sul fate concentration in precipitation sixfold. Robert J. Charlson of the University of Washington, Seattle, said that quantitative understanding of rain water composition requires the inclu sion of both chemical and physical fundamentals either in measurement activities or in theoretical models. Charlson uses the term "washout ratio ( # 0 , " where _ moles of χ per m 3 of air moles of χ per m 3 of non-cloud air While highly variable, W often has a value of 10 6 , implying that one mL of water scavenges one cubic meter of air. Most clouds do not rain; rather, they evaporate, leaving behind the solute in the form of aerosol particles. Eventu ally, however, most of these are re moved from the atmosphere in rain, often a thousand or more kilometers from the place where the particles or particle precursors were introduced to the atmosphere, Charlson says. One useful comparison can be made between rainwater in pristine settings and that in polluted or industrialized settings. It is not generally possible by this simple comparison to deduce how much SO2 oxidation or other reaction may have occurred; it is possible, however, to demonstrate the relative importance of natural factors in com parison with polluted sources. Michael R. Whitbeck and col leagues at the Desert Research Insti tute ( D R I ) in Reno, Nev., said that chemical reactions occurring in cloud droplets are believed to have profound
effects on the chemical composition and acidity of precipitation. These re searchers described the formulation of a numerical model that combines cer tain features of • cloud droplet nucleation and growth, • gas transport and aqueous chemical reactions, and • their specific use as a tool for in terpreting the chemistry occurring within cloud droplets, as observed in cloud simulation experiments. The investigations were performed in the DRI expansion chamber. Model calculations were compared with re sults of cloud chamber experiments for a variety of experimental conditions. There are uncertainties in numerous models; kinetic and mechanistic details are missing. They also delineated data needs for future modeling of cloud chemistry. William E. Wilson of the EPA (Research Triangle Park, N.C.) spoke about the presence of hydrogen per oxide in simulated dew and rainwater. Hydrogen peroxide is an important trace gas in the troposphere. It can act as a sink for hydroperoxyl radicals and, upon photolysis, it can be a source of hydroxyl radicals. In addition, hydro gen peroxide may play a major role in the oxidation of SO2 to sulfuric acid. T h e simulated dew samples were col lected from ambient air and from smog chambers. Nevertheless, for each ex periment, the hydrogen peroxide con centrations in the ambient air and in the smog chambers were not appre ciably different. Gregory L. Kok of N C A R (Boul der, Colo.) said that the reaction be tween sulfur dioxide and hydrogen peroxide has been examined in great detail recently and appears to be the primary pathway for the oxidation of sulfur(IV) in the environment. Only a few studies have been done on the sulfur(IV)-hydrogen peroxide reac tion to look for catalysis or inhibition. Kinetics measurements on the reaction of hydrogen peroxide and sulfur(IV) were made by monitoring the loss of hydrogen peroxide after the addition of a known amount of sulfur(IV). Kok's study showed that the sulfur (IV)-formaldehyde adduct is resistant to oxidation by hydrogen peroxide under conditions that typically would be encountered in cloud chemistry re actions. L. W. Richards and colleagues at Sonoma Technology, Inc. (Santa Rosa, Calif-) said that liquid-phase reactions may play an important role in the conversion of sulfur dioxide to sulfate. They measured cloud droplet Environ. Sci. Technol., Vol. 17, No. 6, 1983
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size distribution with the AASP-100, a particle measuring system. The ex perimental data showed the presence of hydrogen peroxide and sulfur diox ide in all cloud water samples, indi cating the inhibition of the fast reac tion between these species. Their re port focused on the combined con centrations observed in the filter and cloud water measurements. Because of the limited aircraft flight time, it was not possible to follow air parcels during cloud formation in order to determine the relative importance of chemical conversion processes in clouds and in the prior day's photochemistry. Combustion emissions At the symposium on organic emissions from combustion, Clarence L. Haile of the Midwest Research In stitute talked about the nationwide survey of stationary combustion sources. Figures on emissions from seven power plants were presented. Flue gas samples were collected with the EPA Method 5 trains, and several polynuclear aromatic hydrocarbons (PAHs) were identified in coal and flue gas samples. Polychlorinated bi phenyls in the form of tetra- through octachlorinated biphenyls also were identified in samples of flue gas and plant background air samples. Nationwide emissions of specific organic pollutants from coal-fired utility boilers were estimated from the results of the survey. The survey was designed on the basis of results of a two-plant pilot study of emission variability. The two plants, a coal-fired utility boiler and a heat recovery mu nicipal refuse incinerator, were sam pled for 21 and 11 days, respectively. Samples of fuels, ashes, and aqueous specimens were collected as often as six times daily, using a statistically de signed protocol. The specimens were analyzed for total extractable organic chloride (TOC1), which was used to assess the variability of emissions (and inputs) during each day, over a num ber of days, and between the two plants for each medium. Marcus Cooke and colleagues of Battelle's Columbus Laboratories measured PAHs in boiler gas streams of all coal-fired stoker boilers. Source Assessment Sampling System (SASS) trains were used to collect the samples. Seventy-four elements and 21 PAHs were characterized in this study. Marcus and co-workers also assessed the presence of PAHs from residential coal and wood stoves burning anthra cite and bituminous coals. In this sec ond study, samples were collected with a modified EPA Method 5 train. Data 244A
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Smokestacks. A nationwide survey of emissions from seven power plants showed that polynuclear aromatic hydrocarbons are emitted.
were presented showing a number of individual PAHs in each of the six stove tests. More information on PAHs will become available at Battelle's 8th an nual meeting on the subject, which is scheduled for Oct. 26-28. The keynote speaker will be Lorenzo Tomatis, head of the International Agency for Cancer Research in Lyons, France. His agency is part of the World Health Organi zation. The number of compounds available for PAH analysis has in creased from 13 in 1972 to 47 today. All told, the agency has found a mere 12 compounds (not limited to PAHs) to be carcinogenic to humans. A. C. Barefoot of Dartmouth Col lege, N.H., found 13 PAHs in ambient air particulate matter associated with residential wood combustion. The principal site for ambient air sampling was Lyme Center, N.H., a rural village with a population of 300, located about 15 miles north of Hanover. Analyses were performed by HPLC with UV detection and GC/MS. The results were obtained during a two-week pe riod (Jan. 16-Feb. 1) of constant sampling at four sites. The lowest concentration of PAHs, found at Brigham Hill, gave an average benzo[a]pyrene reading of about 1 ng/m 3 , while the residential area in Hanover showed the highest average, 3 ng/m 3 . Greg A. Jungclaus and co-workers at the Midwest Research Institute described a Volatile Organic Sampling Train (VOST) that was developed in response to the need for a better sam pling system for volatile organic com pounds. These constitutents are gen erally important components of stack
effluents. The Jungclaus group's paper presented details of the design of the field version of the VOST. But neither this sampling train nor integrated gas bag techniques have been validated, so it is not possible to state which is more correct when the values disagree. Al though the values have agreed within a factor of two, VOST generally ov erestimates concentrations for higher molecular weight compounds. V. Lopez-Avila and co-workers at Acurex Corporation (Mountain View, Calif.) said that the EPA had spon sored subscale tests to identify and quantitate boiler operational param eters and to determine their effect on how efficiently hazardous materials are destroyed. The Acurex program involved 74 different firing conditions. The effects of firing parameters on thermal profiles and destruction effi ciency have been quantitated for a subscale unit. Detailed results from the tests were presented. P. M. Walsh and colleagues at MIT looked at the combustion rates of methane and naphthalene in the free board of a fluidized bed combustor. The particle size distribution of the entrained particles was measured to determine if this mechanism for naphthalene combustion in the free board will be substantiated under closer examination. Anton Chin and co-workers at the Naval Weapons Support Center (Crane, Ind.) looked at the combustion products from devices that produce different colored smokes. These com bustion products have been identified as PAHs resulting from the thermal decomposition and thermal rear rangement of the parent dyes. E. D. Erickson and co-workers at the Naval Weapons Center (China Lake, Calif.) were involved in the analysis of detonation products from nitrotoluene. Diesel exhaust emissions have re ceived considerable attention recently. Diesel engines emit 30-50 times more particles than comparable gasoline engines. Moreover, 95% of these par ticles are less than 1 μιη in size, and hence are respirable. W. E. Bechtold and co-workers at the Lovelace Biomedical and Envi ronmental Research Institute (Albu querque, N.M.) studied the separation of diesel particulate extracts and iso lation of fractions of high mutagenic activity. Samples were obtained from the exhaust of a test stand diesel en gine. Nitrated PAHs, including nitropyrenes and nitrofluoranthenes, showed high mutagenic activity. —Stanton Miller
