(18) Larson, R. J.; Perry, R. L. Water Res. 1981,1.5,697. (19) Pirt, S. J. “Principles of Microbe and Cell Cultivation”; Halstead Press: New York; p 33. (20) Larson, R. J.; Clinckemaillie, G. G.; Van Belle, L. Water Res. 1981,15,615. (21) Jenkins, L. K. L.; Cook, K. A.; Cain, R. B. J . Appl. Bacterial. 1979,47, 75.
(14) Tobin, R. S.; Onuska, F. I.; Anthony, D. H. J.; Comba, M. E. Ambio 1976,5,30. (15) Seymour, M. D.; Rodriguez, P. A.; Heber, W. D. “Improved Radioactivity Detector (RAD) for Gas Chromatography”, presented a t the 171st National Meeting of the American Chemical Society, New York, April 1976. (16) Larson, R. J.; Payne, A. G. Appl. Environ. Microbiol. 1981,42, 621. (17) Games, Larry M.; Staubach, Jean A. Enuiron. Sci. Technol. 1980,14,571.
Received for review April 13,1981. Accepted August 17, 1981.
Biogenic Sulfur Source Strengths Donald F. Adams” and Sherry 0. Farwell Department of Chemical Engineering, University of Idaho, Moscow, Idaho 83843
Elmer Robinson, Merrill R. Pack, and W. Lee Bamesberger Department of Chemical Engineering, Washington State University, Pullman, Washington 99 164
Conclusions are presented from a 4-yr field measurement study of biogenic sulfur gas emissions from soils, and some water and vegetated surfaces, at 35 locales in the eastern and southeastern United States. More than one soil order was examined whenever possible to increase the data base obtained from the 11major soil orders comprising the study area. Data analysis and emission model development were based upon an (80 X 80)-km2 grid system. The measured sulfur fluxes, adjusted for the annual mean temperature for each sampling locale, weighted by the percentage of each soil order within each grid, and averaged for each of the east-west grid tiers from 47”N to 25”N latitude, showed an exponential north-to-south increase in total sulfur gas flux. Our model predicts an additional increase of nearly %-fold in sulfur flux between 25”N and the equator. Introduction
Sulfur compounds, in both the gaseous and aerosol phases, are ubiquitous in the atmosphere. The atmospheric sulfur burden comprises the sum of the global contributions from anthropogenic and natural sources. Anthropogenic source strengths have been computed with reasonable accuracy from fuel-consumption data for power plants, industry, transportation, and comfort heating and from emission inventories for industry including metal smelting, pulp and paper, petroleum refining, etc. Less well-known are the compositions and strengths of the natural sulfur emissions of marine, volcanic, and biospheric origin. Until recently, in the absence of comprehensive field measurements of natural sulfur sources, most natural source strength estimates have been inferred by circumstantial reasoning to be the difference between the anthropogenic sulfur contribution and global deposition of sulfur from the atmosphere. This approach has provided a wide range of estimates. It was recognized that, even during periods of little or no volcanic activity, a layer of sulfate aerosol exists near 17-20 km ( I ) which exceeds the anticipated contributions from the anthropogenic source strengths. The various proposed global sulfur cycles have several characteristics in common, including a required natural sulfur input from terrestial and oceanic processes to account for this sulfate a t the boundary layer. The biogenic component of the natural sulfur emissions arises from biological activity in soils, water, and vegetation and consequently represents widespread, diffuse global sources. This paper presents the first systematic and comprehensive biogenic sulfur source emission measurement data for a wide variety of soil orders. These data were obtained during an 0013-936X/81/0915-1493$01.25/0
@ 1981 American Chemical Society
extensive measurement study conducted in the eastern and southern United States from 1977 through 1980. The primary objective of this study was to provide quantitative measurements of biogenic sulfur source strengths, including compound speciation, for the major soil orders and suborders within this study area. Thirty-five representative locales were sampled under existing weather conditions to provide essential, basic data defining the seasonal range of biogenic sulfur compound emissions from soils for input into an atmospheric sulfur model having resolution of 6400 km2 (2). This resolution is based upon the (BO X 80)-km2grid system used in the Electric Power Research Institute Sulfate Regional Experiment (EPRI/SURE) study (2).We extended the initial grid system southward in 1979 to include the states bordering the Gulf of Mexico for the purposes of this field study, and then to the equator in 1981 to aid in developing predictions of global biogenic emissions based upon our measurement data within the latitude range of 25-47”N. Samples were collected over a &day period at each of 32 locales and at three selected sites for two or three &day periods during the year to determine temperature-related (seasonal) variations in sulfur flux. Thus, this study provides the most comprehensive information available to date describing the range of biogenic sulfur flux from a wide variety of coastal and inland soils in the United States-an area of -4 X lo6 km2, representing nearly 4% of the land surface in the northern hemisphere. This measurement program was designed neither to explain the biogenic sulfur formation reactions nor to examine the variations in the concentration and composition of the measured sulfur fluxes in terms of microbiological activity or anaerobicity of the soils. Experimental Methods
Sampling Site Selection. The soils within the study area range from coastal, saline marshes through poorly drained inland organic soils, to dry mineral soils. The major soil orders and suborders were initially ranked in order of anticipated biogenic sulfur productivity by considering organic matter, aeration, soil moisture, vegetation regimes, salinity, stagnation, and possible pollutant levels of associated water ( 3 ) .This ranking was used in a “forced random” statistical selection ( 4 )of the 35 sampling locales and directed our measurements more toward soils deemed to have the greatest biogenic productivity potential and thus the widest range of sulfur fluxes, while minimizing (but not ignoring) the sampling of soils with a lower potential for production of biogenic sulfur. This procedure, as contrasted with a strict random-number approach to sampling site selection, provided more measurement data Volume 15, Number 12, December 1981
1493
on the range of sulfur fluxes which might be expected from those soils thought to have the greatest range of biogenic sulfur emissions. Sampling Procedure. Readily portable, dynamic chambers were used to enclose known surface areas (3).Sulfur-free, enclosure sweep air was prepared by passing ambient air through a four-stage (or five-stage) solid-phase reactor containing layers of Purafil, Drierite, activated charcoal, soda lime (and molecular sieve in 1979 and 1980). A measured flow of sweep air (usually 30 mL/min) was drawn through a 6-in. (15.2 cm), specially deactivated, Pyrex glass sample loop cooled to -183 “C ( 5 ) .The sampling rate and time were varied with the range of sulfur flux encountered. Sample volumes ranged from 15 to 720 mL. Both 12-V dc battery and 117-V ac portable field sampling packages were used as required. Analytical Procedures. The sulfur compounds, cryogenically concentrated in the deactivated Pyrex loops, were speciated and quantified with a modified Hewlett-Packard Model 5840 flame photometric gas chromatograph (FPD/GC) equipped with a cryogenic oven using a 30-m, OV101, wallcoated, open tubular (WCOT) glass capillary column. The detailed analytical procedure has been published ( 5 ) .Known concentrations of hydrogen sulfide (HzS), carbonyl sulfide (COS), methyl mercaptan (MeSH), dimethyl sulfide (DMS), carbon disulfide (CSz), and dimethyl disulfide (DMDS) were obtained from low loss permeation tubes maintained a t 40 f 0.1 “C in a constant-temperature air bath. Calibrations were conducted daily and weekly to provide least-squares Calibration equations. Statistical Analysis. The least-squares relationships between the measured sulfur fluxes and the independent variables including (a) ambient temperature, (b) soil order, (c) day and night, (d) vegetative cover, and (e) bare soil were calculated by using the Statistical Analysis System (SAS) package (6).The SAS regression program was used to determine the percent of the dependent variable associated with the independent variable relationships. An Amdahl Model No. 47OVO6-11 computer was used. Air and Soil Temperatures vs. Measured Sulfur Flux, Temperature is a major factor controlling the rate of biogenic activity with reactions being slow below 5 “C and generally increasing two- to threefold for each 10 “C increase up to -50 “C (7). Although the sulfur flux is probably more dependent upon soil temperature than the associated air temperature, only air temperatures are available in the published US.or global climatic data. Therefore, we used our 158 sulfur-flux samples having concomitant soil and air temperatures to test the hypothesis that air temperatures could be used to estimate the seasonal sulfur flux from individual measurements and then to extrapolate these measurements to seasonal and annual sulfur fluxes from the average grid air temperatures obtained from the published climatological data (8). Linear regression analysis showed that soil temperature vs. sulfur flux and air temperature vs. sulfur flux had correlation coefficients of +0.685 and +0.647, respectively. Furthermore, there was no statistically significant difference between the two regressions. The linear regression and correlation between the measured air temperatures and associated soil temperatures were also calculated. Other investigators have also shown a direct relationship between measured sulfur flux and temperature (9, IO). These factors all indicate that the fieldmeasured sulfur fluxes for any given temperature may be adjusted to account for the seasonal influence upon sulfur flux by using the published air-temperature data.
Results Soil Order vs. Sulfur Flux. Regression curves for ambient air temperatures vs. sulfur flux were computed for all soil orders studied, forcing a common intercept of 0.0166 g of 1404
Environmental Science & Technology
S/(m2 yr) sulfur flux at 5 “C. These conditions were based upon the known temperature effect upon biological activity and our field measurements. Our 539 samples within the original EPRI/SURE study area during 1977 and 1978 indicated that the sulfur flux for the soil order vs. temperature relationship was best described by three distinct temperature vs. sulfur flux slope regimes ( 3 ) ,as shown by Duncan’s t test ( I I ) modified by Kramer (12) for multiple-range testing of group means having unequal numbers of replications. In 1979 the sampling grid was extended southward from ca. 33”N to 25”N latitude to include the Gulf Coast states, thus providing a common base for expansion of the EPRI/SURE biogenic sulfur model. At the same time, the SURE northsouth grid tiers were renumbered to provide a continuum of two-digit grid numbers from 90”N to the equator to accommodate the measurement data to a global model. A total of 760 field samples were obtained within the 4-yr period. The regression curve computations were repeated for the soil orders sampled using the entire 760-sample data base. This shows only two statistically significant soil groupings for the sulfur flux vs. ambient air temperature regimes. The original definition of “group I” for soils of the coastal wetlands was unchanged. However, we found the slopes of the regression curves for soils defined earlier as “group 11”soils (inland, “wet”, high-organic) and “group 111” soils (inland, “dry”, mineral) were not significantly different when considering the 760 sulfur-flux measurements. Nevertheless, we have retained the three different soil groupings by physical differences, Le., “group I”, “group 11-a”,and “group 11-b”,for the purpose of discussing the relative source strengths of biogenic sulfur in this report. Comparison of Sulfur Fluxes from Inland Soils. Most direct measurements of biogenic sulfur emission have been conducted in marshes, swamps, and saline tidal areas (13-20). Major exceptions are Delmas et al. (9),who reported sulfurflux measurement from three inland soils in France within a latitude band from 43ON to 47”N, and this present study, wherein 27 inland soils were examined in eastern and southern states. The 5 of the 27 inland U.S. soils which were within the 43-47”N latitude zone of our study area were near the following towns: E. Wareham, MA; Elba, NY; Laingsburg, MI; Eagle River, WI; and Zim, MN. The average, total sulfur flux for these five inland U.S.soils ranged from 0.013 to 0.33 g of S/(m2 yr) under the ambient temperatures existing during sampling. The average H2S flux ranged from undetectable to 0.16 g of S/(m2 yr) for these five U.S. soils. This range of measured H2S fluxes compares exceptionally well with the Delmas et al. (9) H2S flux data which ranged from 0.19 to 0.24 g of S/(m2 yr) for the three inland soils in France-Toulous, Val de Loire, and Landes. The average H2S fluxes for all inland soils measured within this latitude zone in the U.S. (this study) and France (9) are 0.06 and 0.04 g of S/(m2 yr), respectively. Estimation of Sulfur Flux by 6400-km2 Grids for the Study Area. The mean seasonal sulfur fluxes were calculated for each of the (80 X 80)-km2grids by using the two regression curves associated with the corresponding soil orders and suborders, adjusting for the mean seasonal temperature of each grid, and weighting for the percent of each soil order present in each grid. The Calculated, four seasonal sulfur fluxes for each grid were summed to provide a projection of the annual sulfur flux for each grid and for the entire continental study area. These data, separated into the three soil groups and subgroups and their associated land surface areas, are shown in Table I. Relative Biogenic Sulfur Contributions from Coastal Wetlands and Inland Soils. The percentages of each major soil order and suborder within each of the (80 X 80)-km2grids in the study area were summed for the soil groupings noted
above. Although there was no statistical difference between our earlier soil groups I1 and I11 on the basis of the 760-sample data array, it is of interest not only to examine the relative biogenic sulfur contributions from coastal wetlands and all inland soils but also to contrast the sulfur contribution from inland soils with high organic content with the sulfur strengths for the drier, inland mineral soils. These comparisons are shown in Table I. The group I soils represent mostly coastal wetlands and comprise -7% of the study's land area and produce nearly 41% of the calculated biogenic sulfur flux for this area. Group 11-a soils, inland soils with high organic matter content existing mostly under "wet" conditions, comprise -18.7% of the land within this study area and are projected to produce -11.3% of the calculated biogenic sulfur flux within this area. The group 11-bsoils have a more typical inland mineral character (drier and lower organic-matter content) and represent nearly 74.3% of the study land area, yet they contribute -47.7% of the biogenic sulfur emissions within the study area. Within this study area, the coastal tide lands-7% of the study area-are the source of -41% of t h e biogenic sulfur emissions while the inland soils-93% of the area-contribute nearly 59% of the biogenic sulfur. This is a significant finding since, before this study and the limited study of inland soils in France by Delmas et al. (9),it was commonly believed that tide flats and intertidal marshes were the primary sources of biogenic sulfur, that inland swamps might possibly be local, but lesser, sources (21),and that dry, inland mineral soils were of no significance in the consideration of biogenic sulfur emissions. This study has shown conclusively that the inland, nonsaline soils of a large land mass such as the eastern and southeastern United States appear to be the source of more than 50% of the biogenic sulfur within that area. I t must be noted that group 11-a and 11-b soils are widely distributed throughout the study-area grids (as contrasted with group I soils which are primarily saline and coastal) and represent extensive, diffuse area sources, whereas the coastal wetlands represent more concentrated line sources. In some meteorological modeling of sulfur impacts, it might be useful to consider these two source configurations, but in the general consideration of global sulfur distribution this may not be necessary. North-to-South Model of Measured Total Sulfur Flux. The calculated annual sulfur fluxes for all land-containing grids in each of the 33 east-west grid tiers within the study area were averaged and plotted against the corresponding grids (Figure 1).This plot shows the exponential relationship with the sulfur flux increasing southward more rapidly from ca. 33"N latitude on a west-east line from about Shreveport, LA, to near Georgetown, SC. This increase in sulfur flux may be due to a number of factors, including the southward increase of the tropical biomass which is conducive to higher organic-matter cycling through the soils, higher annual average airlground temperatures, the increase in wetland areas and associated changes in vegetative types including the appearance of highly sulfur-productive mangrove swamps, and
the extensive fresh to saline water vegetation of the coastal marshlands-all of which have been shown to be directly related to increased biogenic sulfur emissions. The average annual sulfur flux for the 33 east-west grid tiers between 47"N and 25"N latitude (the range of our study area) is best expressed by the following exponential relationship: log Y = 4.70212 - 0.035588X where Y = sulfur flux (tonne of S/(6400 km2)),b = y-axis intercept (4.70212), m = slope of the curve (0.035588), and x = north-south grid identification numbers. Although the above flux model was developed from our data obtained in the eastern and southeastern states from 47"N (grid 80) southward to 25"N (grid 49) latitude, we used this model to predict the total sulfur flux in the 5-7.5"N latitude (grids 20-24). This model predicts that the sulfur flux within this latitude zone should be -8076 tonne of S/(6400 km2 yr). If we further assume that 50-70% of the total sulfur is H2S (based upon our measurements in Florida), our predicted annual average H2S flux for the Ivory Coast of Africa is in the range of 0.5-1.03 g of S/(m2 yr). This predicted H2S flux compares favorably with the annual average H2S flux range gf 0.3-0.88 g of S/(m2yr) reported by Delmas et al. (9) from their measurements. Thus, our model provides an excellent prediction for H2S flux near the equator considering that we are projecting a sulfur flux for the Ivory Coast from our 4725"N latitude data base. Further extrapolation of our model to the equator (grid 15) indicates that the total sulfur flux might be as high as 14 700 tonne of S/(6400 km2 yr) (2.3 g of S/(m2yr)) near the equator. Speciation of Sulfur Compounds in the Measured Biogenic Flux. The high-resolution capability of WCOT capillary column gas chromatography, combined with the wide range of soil orders and vegetation sampled, provides new insight into the complexity of the biogenic sulfur-containing emissions. The chromatograms obtained from the 760 soil surface flux samples have shown from as few as 1to as many as 10 naturally-occurring sulfur compounds within a single sample, depending upon the source. Only six compounds have been identified via single-column chromatography. Identification of the unknown sulfur compounds would have required the field use of a portable GC/MS for the analysis of all samples-instrumentation not available within the scope of this study. The identification of these compounds is not essential to the estimation of the biogenic contribution to the global sulfur cycle because these unknown compounds were not present in all samples and, when present, they generally rep-
Table 1. Summary of Annual Biogenic Sulfur Flux by Sol1 Groupings within the Expanded EPRl Study Area soil grouplngs
I (coastal wetlands) Il-a (inland, high organic) Il-b (inland, mineral) total
sulfur flux, tonne of Slyr
10-5 (land area), km2
40 821 13 450 56 843 119 114
2.56 6.85 27.26 36.6
Volume 15, Number 12, December 1981
1495
Table II. Average Composition of Sulfur Compound Fluxes and Total Sulfur Flux by Soil Orders and Suborders av sulfur flux, g of
solls/locales
H2S
cos
0.06 0.02
0.002
MeSH
DMS
s/(m*
yr)
CSZ
7777 *
DMDS
ZS
saline marshes Aransas W. R., TX Cedar Island, NC (10/77) Cedar Island, NC 15/78) Cedar Island, NC (7/78) Cox's Landing, NC (1 1/77) Cox's Landing, NC (7/78) E. Wareham, MA Everglades N. P., FL Georgetown, SC Jeanerette, LA Lewes, DE Rockefeller W. R., LA St. Marks W. R., FL Sanibel Island W. R., FL Wallops Island, VA nonsaline swamps Brunswick Co., NC Elba, NY Okefenokee W. R., GA wet suborders Ames, IA Clarkedale, AR Georgetown, SC
502.9 74.61 0.94 0.096 0.09 1.31 601.6
0.01 0.02 6.36 0.88 0.004 0.04 0.05 0.0002 0.013 0.001 0.06 0.002 0.03
0.005 0.09 0.047 0.018
0.002 0.007 0.012
Dismal Swamp, NC (5178) E. Wareham, MA
0.046
0.008
Elba, NY Fairhope, AL Fens, MN Lakeland, FL
0.158
0.023
inceptisols Belle Valley, OH Philo, OH
0.029 0.48
0.001 0.07 0.02 1.05 1.10 1.38
0.008 1.23 0.81 1.87
0.003 0.0001
0.001
alfisols Kearnysville, WV R.T.P., NC (wooded) R.T.P., NC (cultivated) Shreveport, LA Stephenville, TX Wadesville, IN
0.97 0.028 0.39 0.22
0.017 0.001
0.01
Yankeetown, IN
1.77 0.60 0.26 0.47
0.147
Jeanerette, LA
mollisols Linneus, MO Shreveport, LA
0.001 0.08 23.45 0.22
0.009 0.060
0.021
0.008 0.001
Laingsburg, MI One Stone Lake, WI
0.22 0.006
0.38
0.024 0.006 0.005
Hastings, FL
Celeryville, OH Dismal Swamp, NC (10/77)
0.0003 6.56 11.65
0.07 0.007 0.04 1.57
0.09 0.16 0.001
0.0003 0.008 0.001
histosols (peat, muck) Belle Glade, FL Brunswick Co., NC
1496
0.02 0.16 139.5
0.002
0.042 0.069 0.044 0.084
0.104
0.005 0.004
0.002 0.003 0.001
0.001 0.006 0.003 0.0007 0.002 0.013 0.006 0.002 0.001 0.003 0.01 1 0.001
0.001 0.01 0.011 0.024
0.009 0.002 0.023
0.003 0.001
0.002
0.01
0.029 0.004 0.003 0.002 0.0002 0.002
0.072 0.003
0.004 0.002
0.073
0.082 0.008
Environmental Science & Technology
0.002
0.002
0.022 0.006 0.022
0.016 0.003 0.005 0.002
0.005
0.003
0.026 0.09 0.001 0.002 0.004 0.01 22.29 0.90
0.0004 0.0005
0.0001 0.002 0.0004 0.136 0.014 0.003 0.008 0.004 0.012
0.005 0.004 0.021
0.005 0.006 0.0003 0.001
0.022 0.001 0.001 0.005 0.003 0.002
0.004 0.0002
0.010 0.001
1.82 152.4
0.073 0.006
5 18.3 0.65
0.05 0.005
0.003 0.07 1.63 0.04
75.7 1.69 0.031 0.66 0.12 3.80 650.9 4.45
0.001
0.14 0.19 0.051
0.0005
0.003
0.18 0.002 0.023 0.0003
0.0007
0.008 0.014
0.0002
0.012 0.12 0.068 0.019 0.058 0.014
0.003
0.004 0.017 0.006
0.52 0.029 0.079
0.0004
0.002
0.0003 0.0002 0.003
0.33 0.17 0.056 0.08 0.056 0.121
0.0005
0.12 0.008 0.12
0.0015 0.0005
0.0001
0.002
0.13 0.005 0.013 0.013 0.004 0.017
0.0014
0.094 0.008
0.002
Table I1 (Continued) solls/locales
H2S
cos
MeSH
spodosols E. Wareham, MA ultisols Calhoun, GA Fairhope, AL freshwater pond Belle Valley, OH a
av sulfur flux, g of s/(rn2 yr) DMS cs2
7777 a
0.013 0.009 0.0005
0.003
0.002
0.01 1
0.001
0.002
0.005
0.07
0.02
0.005
0.028
0.0001
DMDS
ZS
0.0002
0.013
0.0001 0.0003
0.024 0.008
0.002
0.13
Unidentified sulfur gases.
esented less than 1-2% of the total sulfur emissions. Theoretically, however, when these unknown sulfur compounds are identified, they may provide insight and direction to the study of the microbiological reactions involved in the biogenic production of sulfur gases and should suggest additional useful starting compounds for consideration in the computations of atmospheric reaction kinetics. Table I1 lists the average measured sulfur fluxes by compound and for total sulfur which were obtained at each of the 35 sampling locales. When more than one soil order was sampled at one locale, the average sulfur fluxes for the samples obtained from each soil order are tabulated separately. These data represent the measured sulfur fluxes a t the ambient temperature existing at the time of sampling; i.e., they have not been normalized to an annual average ambient temperature. Thus, these data cannot be used directly for estimation of the biogenic sulfur contributions to the atmospheric cycle.
Discussion Global Land Surface Biogenic Sulfur Flux. For the moment, let us assume that the natural sulfur flux from the land as calculated by Eriksson (22) is 110 Tg of S/yr and by Granat et al. (23) is 36 T g of S/yr and these values represent estimates of the upper and lower limits of natural sulfur required by the sulfur cycles proposed through the process of circumstantial reasoning. In making this assumption, one must recognize that there is no clear reason why an alternate assumption is not equally valid-that natural sulfur emissions may not actually be greater than estimated by Eriksson or less than those published by Granat et al. Nevertheless, it is of interest to examine these estimates within the perspective of the recent body of field measurement data which were not available to the authors of the various sulfur cycles. In so doing, we must also consider the influence that two somewhat widely held misconceptions concerning the nature of biogenic sulfur emissions have had upon the development of sulfur cycles and upon the treatment of some of the field measurement data. First, the view that the only significant source of biogenic sulfur is the global marshy areas is shown to be erroneous by the field measurements described above. This present study has shown that the typical eastern and southern U.S. inland soils (93%of the land mass of the area) contribute -59% of the biogenic sulfur. Also, the coastal and inland marshy soils (-7% of the land mass of the study area) contribute -41% of the total sulfur flux to the atmospheric burden of the study area as calculated from the field measurements conducted a t or near 35 base sites. Thus, it is not reasonable to assign all of the land-originating biogenic sulfur to the 2.8 X 1012m2 marshy area of the globe. Second, the most recent projections of global biogenic sulfur from land surfaces have been based upon isolated data ob-
tained primarily within the latitude range of 33-57"N. The only major exceptions to this are the work of Delmas et al. (9) in the Ivory Coast (7.5-5"N latitude) and this present study, which provides a continuum of data from -47'N to 25"N latitude, The significant conclusion from these latter data is the exponential increase in measured sulfur flux between -33"N to the equator which departs significantly from a nearly linear north-to-south relationship previously found between ca. 47"N and 33"N latitude. The sulfur flux increases approximately 10-fold between 35'N and 25"N (Figure 1). Furthermore, based upon the projection of our data to the equator and the measurements of Delmas et al. ( 9 ) ,the biogenic sulfur flux appears to increase by an additional 109-fold between 25"N and 7.5-5"N. These data further predict that the maximum sulfur flux at the equator may be as much as 130-fold greater than the average of the measured sulfur flux between ca. 47"N and 33"N latitude. If we then use our model to calculate global sulfur flux from the land surfaces (24)by 5" latitude belts from 90"N to 90"s latitude, we obfain a land surface sulfur flux in the order of nearly 64 Tg of S/yr. This prediction falls within the upper and lower limits of the "pencil" calculations for biogenic sulfur flux by Eriksson (22) and Granat et al. (23) of 110 and 36 Tg of S/yr. Stated in other units, the average global land surface flux predicted from our measurement base is nearly 0.43 g of S/(m2 yr). This compares with the Granat et al. (23)estimate of 0.27 g of S/(m2yr). Our data thus provide experimentally-derived support to the most recent sulfur cycles based upon circumstantial reasoning. This study has dealt in detail with the biogenic sulfur emissions of wet and arable land areas which we believe are major contributors of biogenic sulfur components to the global atmosphere. There are several aspects of the global biogenic emission pattern which should be mentioned to place our discussion in perspective. However, we do not believe that these considerations will require major adjustments in our projected global emissions. One important feature of the global land surface is the relative significant areas of wet lands, particularly in the tropics, and, in total, constituting -1.9% of the land surface. These are apparently high sulfur emission soils and could increase the total biogenic sulfur emissions calculated from our model. Although we measured biogenic sulfur emissions from coastal wetlands along the Atlantic seaboard and the Gulf Coast of the U.S., our model does not fully account for the potentially higher biogenic sulfur flux from the tropical wetland& even though there appears to be a reasonable comparison between our predicted sulfur flux and the Dalmas et al. measurements for the Ivory Coast. A second land surface feature is the global desert areas which have not been considered in our study. These regions of low rainfall and high mineral soils, representing -19% of the global land surface, are expected to have below-average Volume 15, Number 12, December 1981 1497
sulfur emission rates. Adjustment of our model for the anticipated low-emission desert areas will tend to reduce the sulfur emissions projected by our model which does not contain sulfur emission measurement input from deserts. A third factor not considered in our model is the biogenic sulfur emitted from the surface of the open oceans. Emissions from this source would increase our projected global biogenic sulfur burden. Work by Junge ( 2 5 )in North America, Lodge (26) in the North Pacific, Lovelock in the Atlantic ( 2 7 ) ,and Cadle (28) in Antarctica all indicate the possible contributions of gaseous sulfur from the ocean. Acknowledgment Special thanks are extended to A1 Stankunas and Charles Hakkarinen, EPRI project officers, and to the many persons and organizations providing field sites and electrical power. Reference to commercial products is for identification purposes only and does not constitute an endorsement of these products by EPRI or the University of Idaho (RP856-2) or Washington State Univerity (RP856-1). Literature Cited (1) Junge, C. E.; Chagnon, C., W.; Manson, J. W. J. Meteorol. 1961, 18,81. (2) Mueller, P. K.; Hidy, G. M. “Implementation and Coordination of the Sulfate Regional Exueriment (SURE) and Related Research Projects”, Interim Repori EPRI No. EA-1066, EPRI Project No. RP-862, June 1979. (3) Adams, D. F.; Farwell, S. 0.;Robinson, E; Pack, M. R. “Biogenic Sulfur Emissions in the SURE Region”, Final Report EPRI No. EA-1516, EPRI Project No. RP-856-1, Sept 1980. (4) Russell, T. S.; Washington State University, Pullman, WA, personal communication, 1976. ( 5 ) Farwell, S. 0.;Gluck, S. J.; Bamesberger, W. L.; Schutte, T. M.; Adams, D. F. Anal. Chem. 1979,51,609. (6) Barr, A. J.; Goodnight, J. H.; Sall, J. P.; Helwig, J. T. “A Users Guide to SAS 76”; SAS Institute: Raleigh, NC, 1979. 17) Tauber. H. “The Chemistrv and Technoloev -“ of Enzvmes”: Wilev: New York, 1949. ( 8 ) “Climatic Atlas of the United States”: U S . DeDartment of Commerce: Washington, DC, 1968.
(9) Delmas, R.; Bandet, J; Servant, J.; Baziard, Y. J:Geophy. Res. 1980,85,4468. (10) Hill, F. B.; Aneja, V. P.; Felder, R. M. J . Enuiron. Sci. Health 1978.13. 199. (11) Duncan, D. B. Biometrics 1955,31,1. (12) Kramer, C. Y. Biometrics 1956,32,307. (13) Jaeschke, W.; Georgii, H. M.; Claude, H.; Malewski, H. Pure A P d GeoDhvs. 1978.116.463. (14)’ Aneja, V. P. M.S. Thesis, North Carolina State University, Raleigh, NC, 1975. (15) Aneja, V. P. In “Atmospheric Deposition: Environmental Impact and Health Effects”; Ann Arbor Science Publishers: Ann Arbor, MI, 1980; Chapter 7. (16) Hansen, M. H.; Ingrown, K.; Jorgensen, B. B. Lirnnol. Oceanogr. 1978,23,66. (17) Maroulis, P. J.; Bandy, A. R. Science 1977,196,647. (18) Bandy, A. R.; Maroulis, P. J. In “Atmospheric Sulfur Deposition: Environmenal Impact and Health Effects”; Ann Arbor Science Publishers: Ann Arbor, MI, 1980; Chapter 8. (19) Hitchcock, D. R.; Spiller, L. L.; Wilson, W.E. “Biogenic Sulfides in the Atmosphere in a North Carolina Tidal Marsh”, paper presented a t the American Chemical Society meeting, New Orleans, LA, March 1977. (20) Steudler, P. A.; Peterson, B. J. “Gaseous Sulfur Release from a Salt Marsh”, paper 80-40.3, presented at the Air Pollution Control Association meeting, Montreal, Quebec, June 1980. (21) Hitchcock, D. R. “Biogenic Sulfur Sources and Air Quality in the United States”, Final Report NSF RANN No. AEN-7514571, Aug 1977. (22) Eriksson, E. Tellus 1960,12,63. (23) Granat, L.; Rodhe, H.; Hallberg R. In SCOPE Report 7, Ecol. Bull. 1976,89. (24) “Smithsonian Meteorological Tables”; Smithsonian Institute: Washington, DC, 1965; Vol. 114. (25) Junge, C. E.; Werby, R. T. J . Meteorol. 1958,15,417. (26) Lodge, J. P.; MacDonald, A. J.; Vihman, E. Tellus 1960, 12, 184. (27) Lovelock, J. E.; Maggs, R. J.; Rasmussen, R. A. Nature (London) 1972.237.452. (28) Cadle,R. D.; Fisher, W. H.; Frank, E. R.; Lodge, J. P. J . Atmos. Sci. 1968,25,100. Received for review April 21,1981. Accepted August 17,1981. This work was primarily supported by the Electric Power Research I n stitute under contract RP856-1-2.
Role of Fly Ash in Catalytic Oxidation of S(IV) Slurries Sidney Cohen, Shih-Ger Chang, * Samuel S. Markowltz, and Tihomir Novakov Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
The rate of catalytic oxidation of S(1V) in aqueous fly-ash slurries has been examined by monitoring loss of SOz2- and 0 2 , and S042- formation. Evidence from both filtering and extraction studies indicates that dissolved iron which has been leached from the ash is the chief catalyst. This homogeneous reaction dominates any catalytic effect of the ash surface.
Introduction The catalytic behavior of fly ash in the oxidation of S(1V) in aqueous systems has been reported (1-3). Prior work has considered the potential of fly ash as a scrubber medium ( 2 , 4 ) and suggested how fly ash may function in promoting acid rain formation in droplets ( 3 ) .Although several properties of the ash-surface characteristics, metal oxide content, tracemetal dissolution---have been proposed to account for its catalytic role, no systematic investigation of the nature of the catalysis has been made. It is important to distinguish between surface and homogeneous catalysis-for example, presence of chelating agents in wet scrubbers containing fly ash should inhibit catalysis by leached metals ( I , 5 ) . 1498
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In this study the oxidation of S(1V) in slurries of fly ash has been examined after different ash pretreatment and under varying experimental conditions. Our evidence indicates that dissolved iron is a prime factor in fly-ash-catalyzed oxidation of s02. E x p e r i m e n t a l Section
Reagents. Mallinckrodt or Baker reagent-grade chemicals were used without further purification. The fly-ash types were NBS Standard Reference Material 1633a and four lot samples, referred to as A-D. A is from the TVA Shawnee Power Plant; B, the Duke Power Steam Plant; C, the Jim Bridger Plant, Wyoming; and D, an untreated ash sample obtained from Lawrence Livermore Laboratory. Nanopure water from a Barnstead Deionizer was used throughout. S(1V) Oxidation. The net reaction being studied was S042- H+. The proportional quantities HS03- l/202 of HS03-, S02aH20, and S0s2- vary with pH, so knowledge of the working pH is essential. Unless otherwise stated, the reaction pH was 3.1 f 0.1. Reactions were monitored by using three different methods: (1) in open-air Erlenmeyer flasks agitated with a magnetic stirrer, S(1V) loss being monitored
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@ 1981 American Chemical Society
