MAP3S: An investigation of atmospheric, energy related pollutants in the Northeastern United States

MAP3S: AN INVESTIGATION OF ATMOSPHERIC, ENERGY RELATED POLLUTANTS IN THE NORTHEASTERN UNITED STATES MICXAEL C. MACCI~CXEN Lawrence Livermore Laboratory,

University of California. Livermore, CA 94550. U.S.A.

(First received 13 June 1977)

Abstract-The Multi-State Atmospheric Power Production Pollution Study (MAP3S) is a major new atmospheric research program of the U.S. Energy Research and Developmmt Administration. The goal of the MAP3S program is to develop and demonstrate an improved, verified capability to simulate the present and potential future changes in pollutant concentration, atmospheric behavior and precipitation chemistry as a result of pollutant releases to the atmosphere from large-scale power production processes. primarily coal combustion. A major motivation of this program is to be able to provide those agencies charged with the task of meeting the nation’s energy needs with the knowledge required to assess alternative strategies for generating power while ensuring ample protection of human health and adequate preservation of the natural environment. Since coal is the most abundant domestic fossil energy resource and since electric power pr~uction is a major and growing sector of our energy economy, this study focuses on the effects of emissions from coal fired electric power plants. particularly sulfur oxide emissions The study domain is the high population, energy intensive northeastern quadrant of the United States Research projects are underway to measure present sulfur oxide concentrations and composition, to assess the potential for long range transport, to investigate transformation processes in plumes from point and urban sources, to sample precipitation chemistry and improve und~st~ding of scavenging mechanisms, and to develop numerical models that can simulate future air quality on sub-continental scales given patterns bf anticipated combustion emissions.

1. lNTRODUCnON

Will the acidity of precipitation and atmospheric turbidity increase in the United States with increased coal combustion? Can atmospheric concentrations of particulate sulfur be reduced by reducing suifur oxide emissions? To provide the basis for answering such questions in energy and environmental planning, ERDA’s Division of Biomedical and Environmental Research (DBER) is unde~~ng the MAP3S program to provide the knowledge required to assess alternative strategies for generating power while ensuring ample protection of human health and adequate preservation of the natural ~~ronment (MacCracken, 1977). Over the next several years, in cooperation with programs of other organizations within and outside the United States, the MAP3S program will seek to improve scientific unders~n~ng of the transport, transformation and fate of atmospheric energy-related pollutants as a basis for an improved, verified capability to simulate present and potential future changes in pollutant concentration, atmospheric behavior and precipitation chemistry. Since coal is the most abundant domestic fossil-fuel resource and since electric power production is a major and growing sector of our energy economy, this study focuses on the effects of emissions from coal-fired electric power plants, particularly in the high population, energy intensive northeastern quad*P I?--I 3--w

649

rant of the United States where both average and episode condition sulfate concentrations have been observed to be significant. The extended term interests of the MAP3S program encompass the entire spectrum of pollutants that may be ascribed to fossil-fuel electric power production, including sulfur and nitrogen oxides, oxidants, hydrocarbons, trace inorganic elements and particles. However, a number of reasons have led to assigning priority to study of sulfur oxides and their associated cations during the first three-year phase of the MAP3S program. These reasons include: (1) Sulfur oxides are a major pollutant from the combustion of coal and research into atmospheric effects of these pollutants is of increasing international interest with the prospect for combined efforts of many groups. (2) The potential health and environmental consequences of sulfur oxides have been of interest for a number of years Although uncertainty exists and more research is needed (e.g. Comar and Nelson, 1975; OTA, 1976). there are certainly preliminary indications that high concentrations of particulate-sulfur can be an important health parameter (e.g. EPA, 1974; Coffin and Knelson, 1976). In addition, precipitation chemistry effects extensively documented in Europe (e.g. Braekke, 1976) are of increasing concern in the United States (Likens, 1976). (3) The setting of an air quality standard for particulate-sulfur appears likely within several years (EPA, 1975),

650

MICHAELC. MACCRACKEN

whereas the health research will probably not be adequate to justify standards for the other pollutants until the 1980s Implementation of an adequate and effective control strategy requires understanding, rather than simple parameterization, of the atmospheric sulfur cycle. (4) ERDA’s contribution to atmospheric research is centralized in the capabilities of the major ERDA national laboratories and several conresearch tract organizations and universities. Research in atmospheric sulfur compounds has become of increasing import to them as the ERDA focus on nuclear energy has broadened to include other energy technologies. The MAP3S program includes researchers at Brookhaven (BNL), Argonne (ANLX Battelle Pacific Northwest (PNL) and the ERDA Health and Safety (HASL) Laboratories, other government agencies the Illinois State Water Survey (ISWS) and several universities. Total support for MAP3S exceeds $3 M per year. (5) The MAP3S program can interface with health, ecology and assessment studies within ERDA. These studies include animal toxicology studies at the Inhalation Toxicology Research Institute, Oak Ridge, Battelle Northwest. among others and ecological effects studies of acid rain on crops, ferns and tree seedlings at Argonne, Brookhaven and Oak Ridge National Laboratories. In Europe, the OECD study (Ottar, 1977) has clearly focused international interest on the problems of long range transport of air pollutants In the United States, similar problems are becoming more apparent and the need for atmospheric research on scales beyond 1OOkm is now recognized by EPA, EPRI and ERDA. Although these organizations and ERDA may have slightly different long-range objectives, the scientific research which is necessary to develop the needed understanding of problems,in North America has much in common. Thus, in addition to building on the work of the European scientific community, MAP3S will coordinate its research program and especially the field experimentation and observation programs, with related activities of EPRI’s SURE program (Perhac, 1978) EPA’s MISTT study (Wilson, 1978) and STATE (EPA, 1977) program and Canada’s sulfate pollution study (Whelpdale, 1978). 2. MAP3S SCIENTIFIC PROCRAMRESPONDING TO UNCERTAlNTY

Although desirable to develop atmospheric research priorities from the requirements of studies of health and ecological effects, available data on some effects are too sparse (e.g. on the response of typical U.S. forest ecosystems to particular characteristics of modified precipitation chemistry) and unwrtainties in such effects are too large (e.g. on what pollutant species cause what health effects) either to l A laboratory sub-program is not included in MAP3S. except to the extent that substantial elforts will be made to improve instrument techniques within the characterization and lield experiments sub-programs

define particular questions or to establish research priorities Specific examples where data are lacking include the relative importance of such factors as long-term average and short-term episodic concentrations, pollutant particle size and composition, and instantaneous or storm average precipitation acidity. Indeed, there seems to be no way to rule out any one process or pollutant species as being significantly more or less important than any other. Therefore, in planning MAP% the approach has been to identify those aspects of the problem where uncertainties remain, and to direct theoretical and experimental studies to the potentially significant pollutants and atmospheric mechanisms controlling the transport, transformation, and removal of energy-related emissions. Conceptually, the tasks that must be carried out in order to alleviate uncertainty and improve understanding of relevant atmospheric behavior are divided into three sub-programs:* (a) Characterization Sub-program: measurement of the chemical and meteorological variables that determine the distribution of pollutant species and that will be needed as input for and as a means of verifying the predictions of numerical models (b) Field Experiments Sub-program: design and execution of those atmospheric research experiments necessary to understand the mechanisms and related processes that must be included in simulation models in order to improve their accuracy. (c) Simulation Sub-program: development, verification and demonstration of the capability to simulate the atmospheric behavior, pollutant concentrations and precipitation chemistry effects of emissions from fossil-fuel electric power production relevant to human health and welfare. It is anticipated that these several sub-programs will be carried out simultaneously, so that, for example, a repertoire of characterization measurements will be being developed even as numerical models are being constructed and tested against measurements being gathered in the field program. The goal of MAP3S includes the development of a verified simulation capability in order to understand the physical processes taking place during the transport, transformation and eventual removal of pollution from the atmosphere by both wet and dry processes. As the models are improved and verified, they will be exercised for various scenarios of fossil-fuel electric power production, including different geographical distributions of fuel use, fuel characteristics. abatement strategies, etc. The results of these studies will be made available for assessment studies which consider effects upon human health and ecology. Ten main elements or tasks in the work program have been identified, covering the three sub-programs mentioned above, and these are set out below. A more complete description of the status of m-cent research in these areas and the extent of uncertainty is contained in the MAP3S Program Plan (MacCracken, 1977)

Energy related pollutants in the northeastern United States

Task 1. Specification and quantification of the emissions

ofatmospheric, energyrelated

(AER) pollutants result& ing from present power production processes and consideration of the spectrum of pollutants that may be emitted as a result of introduction of new processes The Brookhaven National Laboratory (BNL) is using existing data from the Federal Power Commis sion (FPC, 1972), Environmental Protection Agency (NED& 1976) and state emission inventories to develop an emissions data base. The inventory has been divided into the largest 500 point sources (not all of which are power plants) and several thousand area sources representing more than 55,000 smaller point sources in the eastern United States. The inventory includes emissions of sulfur and nitrogen oxides, hydrocarbons and particles. Task 2. Identification and quantification of sources of AER pollutants that do not result directly from power production and of other substances that may aficr the concentration, distribution, transformation and fate of AER pollutants The effort discussed in Task 1 is also developing

an area source inventory in which more than 55,000 small point sources are aggregated into elements, each roughly 30 by 30 km. Emissions from the biosphere are not included, although efforts are underway to identify potential source regions (e.g. marshlands) by identifying land types. Work in this area by other researchers (e.g. Semb, 1978; Mtsz&ros, 1978) and organizations (e.g. EPA, EPRI) will be utilized where possible. Task 3. Characterization of the physical and chemical properries of AER pollutants, including particle size, oxidation state, derivative compounds, molecular form, etc. that are commonly found in the atmosphere

Directly emitted gaseous pollutants (e.g. SO*, NO,.. have been sampled for many years, have been followed out to tens of kilometers downwind from power plants, are reasonably well characterized, and in most cases have been controlled to such an extent that air quality standards are being met. For secondary, or derivative. compounds (such as ammonium sulfate and bisulfate, sulfuric acid mist. sulfite, etc.) most observations have been reflected in measurements of the total suspended burden, with relatively few ana-

651

lyses looking at such properties as molecular form. particle size distribution, acid sulfate speciation, etc. A variety of approaches (see Table 1) are being used in MAP3S to characterize atmospheric sulfur compounds collected throughout the region. The techniques, described more fully by Newman (1978), include: i.r. spectroscopy (Cunningham et al., 1975). X-ray photoelectron spectroscopy (Craig et al.. 1974) and Gran &metric analysis (Tanner and Newman. 1976) to look at such characteristics as particle acidity titration and molecular form; thermochemical (Eatough, 1978) to look for S(IV) compounds (e.g. sulfites); and a diffusion battery (Marlow and Tanner. 1976) to provide samples for analyses of composition in various particle size categories. Figure 1 shows the present network, for example. of Lundgren impactors. filters from which will be analyzed routinely by i.r. spectroscopy and occasionally by other methods. Task 4. Determination of the spatial and temporal distribution of AER pollutants under both average and extreme conditions

For data on surface concentrations of pollutants, MAP3S will rely largely on the SURE network (Perhat, 1978; Hidy and Mueller, 1978) and available measurements from state agencies. MAP3S will utilize the BNL and PNL aircraft to provide data on the horizontal and vertical patterns of pollutant concentration in the planetary boundary layer. When passible, these flights will be in conjunction with aircraft sampling (primarily in the vertical) by the SURE aircraft. Flight patterns for the first SURE intensive period (early August 1977) and areas for possible future flights are shown on Fig. 2. We anticipate data from these flights to provide information on the time and space sdales of sulfate variability and the presence or absencebf plumes of sulfate from major industrialized areas (e.g. the Ohio River Valley).

L = Lundgren impactor P = Pyranometer

Table 1. Particulate sulfur analysis techniques to be applied as part of MAP3S program Ion chromatography X-ray fluorescence Methyl-thymol blue Silver-110 (“‘Ag) precipitate Gran titration Infrared spectroscopy BenzaIdehyde extraction Thermochemical titration Photo-electron spectroscopy

Fig. 1. Location of special turbidity and sulfate acidity instruments sponsored by MAP3S.

652

MICHAEL C. MACCJUCKEN

Fig. 2. Aircraft flight patterns for intensive measurement periods Solid lines indicate tentative flight plans for first intensive period (August 1977). Dashed lines indicate passible future flight patterns to measure fluxes in and out

of region. Double barred lines indicate additional regional boundaries where measurements will be needed. Task 5. Determination of the processes and parameters governing the vertical and horizontal transport of AER pollutants In using the atmosphere as a disposal medium for combustion products, dependence is placed on dispersal in both the horizontal and vertical dimensions. In the U.S., studies downwind of St. Louis (Breeding et al.. 1973; Lowry et al., 1974; Changnon and Semonin, 1975; White et al., 1976; Zak, 1976; Alkezweeny and Powell, 1977; Wilson, 1978). of Milwaukee (Alkazweeny, 1977) and of the East Coast (Brown and Garber. 1976) have indicated that pollutants emitted by cities form plumes extending at least 100 km downwind. Early analyses for the SURE program show correlations of pollutant level and sulfur oxide emissions from 100 to 300 km, which have been interpreted by Hidy et al. (1976) as evidence for a zone of influence of an individual source of about that size. Visibility and trajectory studies (e.g. Wexler, 1950; Volz, 1969; Hall et al., 1973; Husar et al., 1976) and radionuclide tracer releases (e.g. Knox et al., 1971; Knox, 1974) have shown transport to even longer distances in the lower atmosphere. Major studies in Europe (e.g. Bolin et al., 1971; Ottar, 1978; Prahm et al., 1976) have clearly demonstrated the importance of long range transport in the atmospheric sulfur problem. Preliminary data also indicate that very long range transport from North America to Europe may be occurring (Nyberg, 1976). Much of this work is discussed by Pack et al. (1978). The dispersal of pollutants is equally complex in the vertical dimension. Diurnal changes in atmospheric stability lead to the vertical dispersal of pollu-

tams up to several kilometers during daytime mixing periods and then isolation of pollutants aloft as low level nocturnal inversions are formed (e.g. see Hess and Hicks 1975) Depending on wind speed and direction, these isolated layers can be transported long distances during night-time hours, as was documented by a daVinci balloon experimental flight in 1976 (Zak. 1976), before daytime mixing again brings the pollutants into contact with the surface For investigation of horizontal dispersal mechanisms, ERDA is supporting a cooperative effort among ARL, BNL, HASL and LASL to develop a practical system for sampling and analysis of special tracers at very low concentrations. Field tests of prototype instruments in April at Idaho Falls intercompared five tracers (SF6, two deuterated methanes and two pertluorocarbons) using the new pet-fluorocarbon detection instruments developed by J. Lovelock. Preliminary results show good agreement between SF6 and the perfluorocarbons at 50 km. A recent field program at ANL has looked separately at early morning inversion break-up and early evening reformation and has been expanded to study a several day continuous period in the late summer of 1977. A number of earlier field experiments have indicated a high degree of stratification associated with inversions, including layers of local maxima in pollutant concentration. It is likely that in stable flow, such as is characteristic of nights in the midwestem United States, such layers of pollutants may be free to travel for considerable distances without being subject to significant vertical dispersion. To complement these empirical approaches to understanding atmospheric transport phenomena, numerical modeling studies are underway. Meyers et al. (1976) have developed a diagnostic mesoscaie model employing mass and total energy conservation constraints which provides self consistent wind field and mixing height fields in a layered structure through the troposphere. This work should provide improved wind field and vertical mixing information for use in trajectory and grid models. Field experiments with increased meteorological data and including tracer experiments are being considered for use in validating the performance of this approach. Task 6. Identification of the chemical and physical transformation processes affecting AER pollutants and determination of the rates and mechanisms controlling these processes

Both reductions in emissions and a variety of indirect control measures (e.g. tall stacks, rural location of power plants, etc.) have been used to attain acceptably low atmospheric concentrations of those pollutants which are directly emitted by power plants. Unfortunately, this approach to improving air quality has not succeeded in reducing some of the secondary species (e.g.. sulfate) formed as a result of chemical and physical transformations taking place in the at-

653

Energy related pollutants in the northeastern United States

mosphere after emission. This non-linearity, for example, between emissions of SO2 and concentrations of SOi- (as shown in data discussed by Aftshuller, 1976) requires that an understanding of detailed mechanisms and rates be established The MAP3S program is carrying out point source and urban plume studies in order to broaden the data base upon which the varied hypotheses of transformation mechanisms may be tested. Sampling of point source plumes by BNL will continue (some in conjunction with EPRI) under an expanded range of atmospheric conditions. Forrest and Newman (1977) have reported results from sampling the Labadie power plant on 21 different days that provide little evidence to distinguish between conversion mechanisms (Fig. 3). Sampling under conditions involving higher humidities, winter sunlight, more particulate matter (as recently done at the AnClote plant in Florida), increased mixing, and a larger range of temperatures will apparently be needed to allow correlation of conversion rates with atmospheric conditions and to deduce information on conversion mechanisms. Studies of conversion rates of SOz to SOideduced in urban plumes indicate that such conditions may be more conducive to conversion than in point source plumes. To expand the available data base, a study of the Milwaukee urban plume is underway by PNL. Under west wind conditions this plume is carried across Lake Michigan and, when the air is warmer than the lake surface, can be isolated from both interaction with the surface and introduction of fresh pollutants At about 100 km, the plume again comes over land This can initiate increased mixing and contact of the polluted air with the surface, thus providing altered conditions from which to draw conclusions.

D~stoncc

from

stack.

km

Fig. 3. The observed conversion rate of SO, to sulfate with distance on twenty-one different days for the Union Electric Company power plant in Labadie, Missouri (Forrest and Newman, 1977). Possibly because of a limited range of atmospheric conditions, no distinct correlation could be found between the extent of SO2 conversion and distance, travel time, temperature, relative humidity, time of day, or atmospheric stability.

I

I

I

I

6119

-

---- - - - - -.

120 -

O-0 u 1

8121 8123 8124 8127 8/28 - a/30

2 3 4 Time after first pass, hr

5

6

Fig 4. Vertically averaged ozone concentrations Milwaukee urban plume versus time (proportional tance) in August 1976.

in the to dis-

Results from the August 1976 sampling of the Milwaukee plume indicate that ozone and sulfate are forming as the air mass ages (Fig. 4), while SOz, NO, and NO2 are decreasing. The SO1 to SO:- transformation rate on 27 August reached 6.8% h-’ with a peak 0, concentration of 108ppb, whereas on 28 August the conversion rate was approximately zero with 49 ppb peak 0, (Alkezweeny, 1977) Lead concentrations were almost four times as great on 27 August, indicating greater contributions of automobile exhaust products to the pollutant mix and suggesting the importance of chemical radicals in the reaction scheme (Walter et al., 1977; Isaksen et al., 1978). Layers of increased sulfate concentration were also found at about 3000 m on days when the wind was from the northeast, perhaps indicative of long range transport. Results from flights during the summer of 1977 in the same region are now being analyzed. In addition to the plume studies, direct mechanistic studies have begun at ANL in which determination of the oxygen isotope ratio in SO, and sulfates is used to determine the chemical paths that occurred during transformation processes (Cunningham and Holt, 19763. Laboratory testing on the technique is being augmented by analysis of field samples. Task 7. Determination chemical tants from

of the rates of physical

mechanisms governing the atmosphere

removal

and bio-

of AER

at the earth’s

surface

pollu(dry

deposition)

As discussed by Garland (1978). gaseous and par-

MKHAEL C.

654

ttculate pollutants are removed at the earth’s surface by a variety of processes. The rates of removal appear to be related to such variables as surface character (land or water, vegetation type and condition, roughness, etc.), atmospheric stability (Hicks and Liss, 1976). turbulence, time of day, pollutant concentration. and other factors (Wesely and Hicks, 1977). ERDA and EPA are supporting joint experiments over various types of terrain to look at gas and particle fluxes to the surface. The work is based mainly on the eddy correlation technique in which analog signals from fast-response sensors of the vertical and horizontal wind components, temperature and particle concentration are combined to produce eddycorrelation measurements of the vertical fluxes of momentum. sensible heat and particles (Hicks. 1970). Preliminary measurements indicate that deposition velocities appropriate for the transfer of particles of about 0.1 pm diameter are not greatly dissimilar from those accepted fror the transfer of sulfur dioxide (Wesely rt al.. 1977) These direct flux measurements over grassland appear to contradict earlier work, generally over smooth surfaces (Garland, 1978). Additional field experiments over a forest canopy, however, seen to confirm these higher estimates for sulfate deposition (Wesely, 1977). Because, preliminary mode1 experiments (e.g. Sheih, 1977) indicate that variation of the rates of these dry deposition processes can have substantial effects on downwind concentrations of pollutants and the concentrations of their derivative products, further experiments are planned to evaluate deposition velocities for a variety of atmospheric contaminants and size distributions over a range of natural surfaces. Measurement techniques will include conventional eddy-correlation and profile methods. as well as less familiar variance and spectra1 density approaches Task

8. Identification

rrning

the removal

of the mechanisms and rates gooof AER

scavenging and determination lutants

on trace

chemistry.

material

specifically

pollutants

by precipitation

of the effects of AER palbalances

and precipitation

including the acid-base

relation-

ships

Although precipitation is episodic and highly spatially variable, the great effectiveness of the wet scavenging process causes precipitation to be an Important sink process for atmospheric pollutants. In addition, the relatively high levels of pollution in the northeastern United States can have an important effect on the chemical balance of the precipitation. bodies of water, and the earth’s surface. Papers by Garland (1978), Hales (1978) and Granat (1978) prowde recent reviews of the present state of knowledge and the extent of seriously acidified precipitation (see also FISAPFE, 1976). As part of MAP3S, a complementary program of observations and field experiments has been initiated to address both what is occurring and what mechanisms are leading to the observed results. The observa-

MACCRACKEN tion program will involve scales ranging from regional to interstate. MAP3S is currently supporting ISWS in the completion of data analysis for the multiyear METROMEX project 100 km around Chicago. As part of the new Chicago Area Program (CAP), MAP3S will be supporting analysis of contaminants in precipitation in order to better understand pollutant mass balances from the large Chicago metropolitan area. On the inter-state scale, a high-quality prototype precipitation chemistry network is being established in order to evaluate the chemical composition and properties of precipitation in the northeastern states where there are indications that ‘acid-rain’ is becorning an increasingly serious problem. Unlike Scandinavia, there has not been a long-term record of precipitation quality developed over a wide region. The MAP3S network is envisioned as the first step in establishing a more complete, more extensive, and longer term U.S. network (Cowling, 1975). As a prototype network, special care is being taken to evaluate needed procedures (Hales et al., to be submitted), compare collection techniques, and investigate the need for collecting on an event basis as opposed to a monthly basis. This last factor will allow correlation of pH with the trajectories of the storms, thus permitting an analysis of the source of precipitated pollutants. A list of species for which the precipitation samples are being analyzed is given in Table 2. In late 1976. samples were located along a north-south line of four university-operated sites from upper New York State to Virginia (see Fig. 5). Four additional sites will be established in 1977. In order to improve understanding of scavenging processes PNL and cooperating universities are investigating the mechanisms by which pollutants are scavenged from the atmosphere by precipitation (Hales, 1978). The initial focus is on stationary storm systems. such as lake effects storms, where aircraft measurements can be combined with a surface network in well-defined experiments. For example, it is anticipated that the Milwaukee urban plume, the characteristics of which have been measured under fair weather conditions for Task 6. will intersect lake effects storm systems. This will allow study of the interaction of scavenging processes with pollutants of interest. Special tracers will also be used to determine pollutant pathways. Table 2. Measurements to be made on precipitation

samples collected in the MAP3S interstate precipitanon chemistry network Total acidity Conductivity and pH(H’) so:-. so:NO;, NO; NH:, Na*. K+, Mg’+, Ca’+ PO:F-. ClDissolved Al

.-

Energy related pollutants in the northeastern United States

Fig. 5. MAP3S precipitation chemistry network. The boxes Cl indicate sites established in 1976 and the asterisks l sites being established in 1977. The range of observed pH at the four existing sites is shown for the period November 1976 to April 1977 based on laboratory measured concentrations of hydrogen ion. In association with these observation and field studies, closely related numerical modeling studies are underway at PNL, ANL, BNL and ISWS. in order to develop insight into parameterization of the precipitation scavenging mechanism Chemical transformation within raindrops is also being numerically modeled at BNL.

Task 9. Determination of the effects of AER pollutants upon weather and climate, including effects on visibility, radiation transport, and the amount and extent of precipitation Although effects of urban areas on local scale precipitation and weather are beginning to become apparent, the impact of pollutants on the day to day weather, and therefore ultimately possibly on the climate, over the regional and continental scale is very poorly understood and the proposed climatic impacts remain largely speculative. Reduction of visibility is probably the most noticeable effect, and there is growing evidence relating energy-related pollutants to such effects (e.g. Waggoner et al., 1976). It has been suggested that injection of pollutants higher into the boundary layer by use of tall stacks has led to deeper layers of polluted, low visibility air. Then, in turn, the atmospheric residence time of pollutants is extended because elevated layers can be isolated by low-level nocturnal inversions. This lengthened opportunity for pollutants to be transported and transformed may contribute to visibility obstruction over large areas. While visibility reduction can be an aesthetic and air safety problem, it is probably the impact of the aerosol on the atmospheric heating and cooling patterns that may have the most significant effects. Changnon et al. (1975) and Bohn and Charlson (1976) have suggested that the reduction in solar radiation reaching the surface caused by increased levels of

655

tropospheric aerosols may reduce the length of the growing season by from several days to several weeks In addition to changes in total solar radiation, the ratio of diffuse to direct radiation is changed (Wesely and Lipschutz_ 1976). which may also lead to responses in plants Whether the redistribution in solar energy absorption induced by aerosols leads to further climatic effects remains uncertain. In addition, the extent to which these effects compare with the normal variability of such factors on a year to year basis has not yet been determined The potential effects of increased atmospheric aerosols on the precipitation mechanism has been considered at the Chemist/Meteorologist Workshop in 1975 @lade et al., 1975). Because mechanisms are poorly understood, details are not clear, but the potential elfects appear significant. Not only is precipitation chemistry affected, as discussed in Task 8. but cloud processes (including coagulation, nucleation, cloud condensation nucleii formation, and other aerosol surface phenomena) can be altered, leading to suspected changes in precipitation patterns and amount. Possible changes in dew frequency and fog formation, which in turn catalyze various plant diseases, also may occur. Although these weather and climate problems are potentially as sign&ant as somewhat better defined health and ecological effects, they are not yet the focus of adequate research attention. The only MAP3S project in this area involves location of network of silicon cell pyranometers in the northeast to evaluate the impairment of direct solar radiation by tropospheric aerosols (Wesely, 1975). The sites presently instrumented are shown in Fig 1. If persistent and large effects are seen, further investigation of the changes in the radiation pattern will be encouraged using numerical radiation transport models.

Task 10. Development, verification and demonstration of methods (numerical models) that will make possible accurate assessment of the atmospheric transport and transformation of AER pollutants and of various strategies for generation of power while minimizing atmospheric pollution Assimilation of the knowledge about the various processes and mechanisms controlling air quality is essential if predictive methods (e.g. numerical models) are to be developed for use in simulating changes in future air quality due to changes in emissions. Review papers by Pack et al. (1978). Eliassen (1978) and Fisher (1978) provide a thorough discussion of the major approaches to development of numerical models in the U.S. and Europe. The MAP3S modeling sub-program will pursue a two-pronged approach to improving numerical models The first focuses on upgrading present trajectory models Such Lagrangian models provide the opportunity to undertake a wide variety of sensitivity studies For example, Wendell et al. (1976) have

MICHAELC. MACCRACKM

656

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IO2 - 102*‘pg

q lO2*L

IO2

/m2

pg/rn’

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m

103-103*5~g/m2

I

Io”.5-lo3

cCg/ m2

m c(g m - 2 for an 18 day period m April 1974 for (a) dry removal only. and (c) wet and dry removal using real-time using average precipitation. precipitation

Energy related pollutants in the northeastern

shown that different patterns of deposition on the surface result if rain is assumed to be continuous (as might be done in models attempting to calculate longterm

average

concentrations)

rather

than

episodic

(Fig. 6). The second thrust in model development will be an Eulerian grid model which treats the region as a number of tixed cells approximately 40 km on a

side. Vertically, the model will be designed to simulate the diurnal variation in depth of the surface mixed layer, surface and elevated emissions, topography, wind shear, detailed chemistry and other factors important in multi-day simulations. These models will not be predictive, boundary-layer models, although they may be interfaced with such models. Rather they will be diagnostic, relying on observed meteorological data to drive the transport, transformation and deposition mechanisms

An important aspect of model development is verification. In addition to using specific field experiments to assist in developing detailed parameterizations of specific processes, integrated model results for both the Eulerian

and

Lagrangian

models

will be com-

pared with the observations provided by the SURE network and MAP3S characterization flights Comparisons will be made for both average and episode conditions. Further, MAP3S envisions a few very detailed ‘box budget’ experiments which will attempt to document the flux and fate of pollutants in a welldefined region. These experiments will be compared to model simulations to assess model accuracy. As a final aspect of the modeling program, application of the models to various scenarios of future energy use will be continued. The objective is to have a capability useful in formulating energy policy; thus model application will focus on such questions as the impact of dramatically increasing coal use in the Midwest, the effect of widespread application of flue-gas desulfurization, the impact of Ohio River basin emissions on the New York megalopolis, etc. Although point source plume models will be developed to assist in interpreting field experiment data, the focus will not be on the impact of a single plant, but rather on the effect on a national or regional energy policy. 3. SUMMARY

AND CONCLUSIONS

Because the research needed to resolve the scientific uncertainties is substantial, the resources required to meet these needs are also large. It will require the combined resources and talents of researchers around the world acting with cooperation and coordination ifan efficient and effective approach is to be successful in addressing the scientific uncertainties. In the United States this involves particularly the cooperation of EPA, EPRI and ERDA. Because North America also has international frontiers, coordination between U.S. and Canadian programs is anticipated. The emphasis in MAP3S supported researdh will be on field experiments aimed at improving understand-

657

United States

ing of atmospheric processes, numerical modeling aimed at simulating what is happening, and, with substantial reliance on the SURE surface network. in assisting to characterize present air quality. Acknowledgements-As project director for MAP3S, I have heen assisted by a steering committee selected from Project participants including Drs Leonard Newman, Paul Cunningham, Jake Hales. and Larry Wendell and Bruce Hicks and Ron Meyers. ERDA’s program in sulfur studies is due in large part lo the support of Mr. David Slade, Deputy Program Manager for Environmental Programs. ERDA. This work was performed under the auspices of the U.S. Energy Research and Development Administration under contract No. W-7405-Eng-48.

REFERENCES

Alkezweeny A. J. (1977) private communication. Alkezweeny A. J. and Powell D. C. (1977) Estimation of transformation rate of SO2 to SO, from atmospheric concentration data. Atmospheric Environment 11, 179-182. Altshuller A. P. (1976) Regional transport and transformation of sulfur dioxide to sulfates in the U.S. J. Air Pollut. Control

Assoc. 26, 318-324.

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