Effects of Acid Rain on Indoor Zinc and Aluminum Surfaces - ACS

14 Effects of Acid Rain on Indoor Zinc and Aluminum Surfaces 1

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J. D. Sinclair and C. J. Weschler 1

Downloaded by UNIV OF SYDNEY on October 22, 2015 | http://pubs.acs.org Publication Date: September 25, 1986 | doi: 10.1021/bk-1986-0318.ch014

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AT&T Bell Laboratories, Murray Hill, ΝJ 07974 Bell Communications Research, Lincroft, NJ 07738

Acidic precursors of acid rain can readily penetrate buildings. Regions of the United States where "acid rain" has been identified as a problem will most likely have elevated concentrations of such precursors that may influence indoor surfaces. If the available information on outdoor, indoor, and surface concentrations of ammonium, sulfate, nitrate, calcium, and other species is considered, an estimate of the loading above the background can be made for all areas where outdoor concentrations are known. The relative degree of hazard for the different environments can be estimated from the developed methodology and, based on previous experience with zinc and aluminum surfaces, provides a framework for qualitative rankings of comparable environments. For metals and other materials for which surface acidity is often strongly buffered by the corresponding metal oxide layer, the anion loading may contribute more to enhanced degradation than the acidity. This behavior is especially true for top side horizontal surfaces, where coarse alkaline particles will tend to neutralize acidity contributed by anthropogenically derived substances.

The intent of this paper is to present a methodology for estimating, from available information on concentrations and deposition velocities, the potential effects of anthropogenically derived acidic substances on indoor surfaces. Surface accumulation rates are derived that are applicable to all types of indoor surfaces. The discussion of the possible effects of the accumulated substances will concentrate on zinc and aluminum surfaces because data exists on the behavior of these metals in indoor environments (0. Aluminum forms a passivating oxide which protects against corrosion in most environments, while zinc is expected to corrode at a roughly linear rate over its lifetime. The term 'acid rain' is commonly used to describe phenomena associated with both wet and dry deposition. The effects of man-made airborne substances on indoor surfaces are expected to be different from and less dramatic than those on outdoor surfaces. In the outdoor environment, both the species contained in the rain or fog droplets and the added influence of substances previously deposited on the surfaces by dry deposition will impact the surfaces. For very brief rain events, the surface concentrations of many species are likely to be substantial, due to the combined effects of accumulated dry deposition and the high concentrations of species that have been commonly associated with the early stages of a rain event. The available data indicate that roughly 70 percent of the total deposition is dry deposition. Hansen and Hidy (2), in their assessment of existing rain chemistry data, discuss the influence of geographical factors on pH and state that in western arid areas of the United States, soilderived substances elevate the pH in the early stages of a rain event, while in the northeastern 0097-6156/ 86/ 0318-0216S06.00/ 0 © 1986 American Chemical Society

In Materials Degradation Caused by Acid Rain; Baboian, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.


14. SINCLAIR AND WESCHLER Indoor Zinc and Aluminum Surfaces

217

part of the country, anthropogenically derived acidic substances result in rain of lower pH. For long rain events, much of the soluble substances on top side horizontal and vertical surfaces may be eliminated by the continuous washing of the surfaces. Dry deposition will also affect these surfaces between rain or fog episodes, the degree depending not only on the concentrations of species but also on the amount of moisture in the environment and its variability. If the critical relative humidity (CRH) of substances on these surfaces is exceeded or the temperature of these surfaces is sufficiently low that the dew point is reached, the effects of acidic substances are likely to be more dramatic than in dry climates. For the indoor environment, the effects of anthropogenically derived substances on surfaces will usually be limited to those resulting from dry deposition of acidic substances that are able to pass throughfiltrationsystems, to penetrate through leakage pathways or to be carried indoors by humans or various articles that have been outdoors. If the standard indoor environment is taken to be one with (1) closed windows, (2) only occasional opening of doors to the outdoor environment, (3) an air handling system that filters recirculated air, and (4) leakage pathways that remove nearly all particles > 1 μτη diameter, then the effect of a rain episode by itself will likely be limited to an increased rate of degradation associated with a higher ambient relative humidity (RH) and concomitant higher concentration of surface moisture rather than a substantially increased influx of acidic substances. The incoming air may well be somewhat cleaner during a lengthy rain event due to the cleansing effect of the rain on the outdoor pollutant concentrations through impact with particles and solubilization of gases. Very little acidic material in the form of acid rain or fog droplets is expected to enter the indoor environment. The size distribution ranges from 0.5-50 μτη diameter for fog droplets and from 200-5000 μτη diameter for rain droplets (3). Most of the < 1 μτη diameter fog droplets that pass through standard filtration systems are likely to react with air duct walls before entering the indoor environment. The indoor surfaces are taken to be those surfaces that are not associated with the air handling system or leakage pathways. Methodology For Estimating Accumulation Rates For the purposes of this discussion, it is reasonable to assume that the outdoor environment is the source of most of the anthropogenically derived substances (4) that are present in the indoor environment. The accumulation rates of species on indoor surfaces are related to the outdoor concentrations of these substances through the relationships among the indoor and outdoor concentrations and the indoor deposition velocities of these species. A substantial amount of data is available on outdoor concentrations (4-13). Simultaneous measurements of outdoor and indoor concentrations are less numerous. Very few measurements of indoor deposition velocities have been made. Estimated ratios of outdoor to indoor concentrations will be used that are based on field data, where available, or best judgments. From the limited experimental measurements, taking into account the relative variations in outdoor deposition velocities as a function of particle size, indoor deposition velocities will be estimated. Using these approximate indoor/outdoor ratios and deposition velocities, the indoor surface accumulation rates for substances contained in airborne particles can then be estimated from prevailing outdoor concentrations. Estimating the deposition velocities of gaseous species is considerably more complex than estimating those for substances in particles, in part due to the uncertainties in the sticking and reaction probabilities. Such estimates have not been made but the potential effects of some of the typical gases can be surmised from available data on surface accumulation rates, e.g. sulfate accumulation on indoor zinc and aluminum surfaces is predominantly a result of particulate sulfate deposition rather than a corrosion reaction involving sulfur dioxide (O. Concentrations and Deposition Velocities of Acidic Substances As has been documented in a number of continuing and completed studies, the concentrations of the precursors of acid rain and the concentrations of the acidic substances in wet and dry deposition are quite variable from region to region. The anthropogenically derived particles associated with acid rain are expected to have aerodynamic diameters < 2.5 μτη. Such


M A T E R I A L S D E G R A D A T I O N C A U S E D BY ACID

218

RAIN

particles may include sulfate, nitrate, chloride, and ammonium. However, natural coarse particles > 2.5 Mm diameter may also play a role in the effects of anthropogenically derived substances on surfaces. Such particles are typically rich in calcium, are somewhat alkaline, and may neutralize acidity in the man made substances. Concentrations of relevant solid and gas phase species that are likely to be encountered in urban and rural environments are given in Table I (4-13). Background values that would be expected in the absence of anthropogenic

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Table I. Typical Tropospheric Concentrations of Species Associated with Acid Rain (Mg/m ) Species 3

Sulfate Nitrate Chloride Ammonium Calcium Sulfur dioxide Nitrogen oxides Hydrogen chloride Organic acids (formic) Hydrogen peroxide Ozone Ammonia (NH^) 3


3

3

b

Urban

Rural 12

20 4 0.3 5 2 130

6

7

6

25

8

1 2

8 7

2 130

9

8

30 140 20

8

8

Background 6

4 2 0.02

6

7

2

6

5

11

0.6 · 0.2 ·" 0.02 ' 0.2" 5

11

4

,25

3 0.1 0.2 9

8

8

9

0.3 0.05

9

7

9

8

l 60 l

l

1 0

8

8

9

0.1

Fine particle fraction. Coarse particle fraction.

influences are also listed. While the values given are representative of the various environments, deviations from these values will only affect the magnitude of the impact on surface degradation and not the methodology used to examine the impact. The concentrations of solid substances are intended to include the solid materials in the particles, as well as adsorbed materials or substances contained in an aqueous shell. Thus, fine ammonium acid sulfate particles and adsorbed sulfuric acid associated with these and other types of particles contribute to the total sulfate concentration. Table II (4,14,15) reports indoor/outdoor (I/O) ratios for the type of building described in the Introduction. These values should at least provide an indication of ratios to be expected. For the species associated withfineparticles, two different I/O ratios are listed. Thefirstis for structures with standard filtration systems and the second is for buildings with high efficiency filtration systems. To afirstapproximation, such a distinction does not apply to the gas phase species. From these ratios, outdoor data then becomes useful in understanding indoor surface degradation processes. Indoor concentrations based on typical outdoor concentrations are given in Table III. In order to obtain surface accumulation rates from the indoor concentrations, indoor deposition velocities are needed. These are expected to be considerably lower than outdoor deposition velocities, primarily because of reduced turbulence. Data from the authors (4) and other sources (_16) suggest that indoor deposition velocities for substances associated with particles are approximately a factor of 100 lower than outdoor values; this factor has been used to estimate values where experimental data are not available. Values for substances in airborne particles are summarized in Table IV. As discussed above, data are not included for gaseous species.


14.

Indoor Zinc and Aluminum Surfaces

SINCLAIR A N D W E S C H L E R

219

Table II. Typical Indoor/Outdoor Ratios for Office Buildings I/O Ratio Species

Standard Filters

Fine Particles (Sulfate) (Nitrate) (Chloride) (Ammonium)

4

0.3

Coarse Particles (Calcium)


High Efficiency Filters

4

0.07

4

4

0.05

0.02

Sulfur dioxide Nitrogen oxides Organic acids Ozone

14

15

14

15

0.6 ' 0.6 ' 0.6 0.25

14

14

Hydrogen peroxide Hydrogen chloride Ammonia

0.25 0.1 14

1.5

Table III. Estimated Indoor Concentrations of Species Associated with Acid Rain (μ%/τν?) Species

Urban STD

Sulfate Nitrate Chloride Ammonium (NH^ ) Calcium Sulfur dioxide Nitrogen oxides Hydrochloric acid Organic acids Hydrogen peroxide Ozone Ammonia (NH ) +

a

b

1.4 0.3 0.02 0.4 0.04

6 1.2 0.08 1.5 0.1

3

Rural HE

78 7.2 0.6 78 7.5 35 30

Background

STD

HE

STD

HE

1.2 0.6 0.006 0.6 0.05

0.3 0.1 0.001 0.1 0.02

0.2 0.06 0.006 0.06

0.04 0.01 0.001 0.01 0.2 0.06

1.8 0.06 0.02 5.4 0.25 15 1.5

0.25 0.15

STD signifies standard filters. HE signifies high efficiency filters.

Table IV. Estimated Indoor Deposition Velocities (cm/sec) Species

Velocity

a

Sulfate Nitrate Chloride Ammonium Calcium a

3

a

b

4 16

0.004 ' 0.004 ' 0.004 ' 0.004 ' 0.6 '

4 16

4 16

4 16

4

16

Fine particle fraction Coarse particle fraction.


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M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D RAIN

Surface Accumulation Rates To the best of our knowledge, the only measurements of surface accumulation rates of specific species on indoor surfaces have been conducted by us and our coworkers (1,4). These data can be represented in terms of contributions from fine and coarse particles using a procedure described elsewhere (0. Average accumulation rates on zinc and aluminum surfaces derived from studies at eleven urban and three rural areas are given in Table V. Also given in Table V 2

Table V. Surface Accumulation Rates (^g/cm yr) Urban Species

Measured


a

Sulfate Nitrate Chloride Ammonium Calcium

a

b

c

d

e

C

0.17 0.15 0.02 d 0.27

0.76 0.15 0.01 0.19 1.9

C

c

e

Background

Rural

Calculated STD HE

Measured b

0.18 0.04 0.003 0.04 0.77

e

0.07 0.03 0.01 d 0.52

e

e

e

Calculated STD HE 0.04 0.01 0.0001 0.01 0.38

0.15 0.08 0.0008 0.08 0.95

Calculated STD HE 0.03 0.008 0.0008 0.008

0.005 0.001 0.0001 0.001

STD signifies standard filtration HE signifies high efficiency filtration Accumulation due tofineparticles Measurements show that ammonium does not accumulate appreciably on these surfaces after a brief initial exposure. Accumulation due to coarse particles

are calculated accumulation rates based on the indoor concentrations of Table III and the deposition velocities of Table IV. Considering that the experimental accumulation rates are based on a small amount of data and the calculated values result from a series of estimated values, the agreement is good. This procedure for deriving indoor surface accumulation rates from outdoor concentrations provides a means for estimating the degree to which anthropogenically derived substances interact with indoor surfaces in different geographic regions. By comparing the typical urban and rural accumulations rates with the background rates, the contributions due to anthropogenic influences can be calculated. These estimates are given in Table VI.

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Table VI. Surface Accumulation Rates Due To Anthropogenic Influences (Mg/cm yr) Species

Urban STD

Sulfate Nitrate Chloride Ammonium

a

0.73 0.14 0.01 0.18

Rural HE

b

0.17 0.04 0.003 0.04

STD

HE

0.12 0.07

0.03 0.01

0.07

0.01

-

STD signifies standard filtration HE signifies high efficiency filtration


-

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Expected Interactions with Typical Indoor Surfaces As anthropogenically derived substances accumulate on indoor surfaces, reactions with the surfaces and among the substances on the surfaces can occur. The acidity of these surfaces will be a result of a complex interplay among many factors, including the amounts of both natural and anthropogenic acidic and non-acidic substances, and the natural acidity and buffering capacity of the surfaces. The concentrations of natural coarse particles will also affect the acidity and, for this reason, a distinction should be made between horizontal and vertical surfaces. For zinc surfaces, the rate of accumulation of substances is expected to affect the rate of corrosion of the metal. For aluminum in most environments, the passive surface oxide will protect the metal from further significant corrosion. Any interactions that occur on the surface will be among the accumulated substances and perhaps with the outermost layer of metal oxide. Interestingly, a few materials perform better in industrial atmospheres than in clean environments. Suzuki, et al. (17), have discussed the fact that weathering steel utilizes atmospheric pollutants, particularly sulfur dioxide gas, to form protective layers. Prior to considering the effects of man-made airborne substances on indoor surfaces, it is instructive to consider studies on corrosion of metals in outdoor environments. Most of the atmospheric corrosion investigations have used weight gain (or loss if the surfaces are cleaned before weighing) to measure the degree of corrosion. These results have been compared with measurements of specific pollutants 08). For metals that corrode, comparisons between the corrosion rate and sulfur dioxide concentration have shown that a CRH typically in the range of 70 - 80 percent is required for rapid corrosion to occur (18,19), even in the presence of high concentrations of sulfur dioxide. The CRH in this context can be considered as the minimum RH at which the thickness of the adsorbed water film is sufficient for the water to behave like bulk water. The effect of adsorbed moisture on corrosion processes has also been related to time-of-wetness measurements (18). While Mansfeld (20) has shown that the reproducibility of such measurements is subject to variables that are difficult to control, the concept of timeof-wetness is useful for understanding atmospheric corrosion of metals. Rice and Phipps (21) have shown that, for pure metal surfaces, less than a monolayer of water is adsorbed at < 20 percent RH. At 60 percent RH several monolayers can be adsorbed. When the RH is sufficiently high for a moisture film to exist on metal surfaces or on contaminants on metal surfaces, corrosive pollutant gases can dissolve in the moisture film and will then be readily available to react with the metal. Further, the creation of active electrochemical cells between anodic and cathodic areas on the metal surface, possibly caused by particle deposition or other contamination, requires the presence of moisture. The aqueous corrosion literature (22) provides a further basis for understanding some aspects of the surface degradation of metals. Examination of the Pourbaix diagrams (23) for the zinc-water and aluminum-water systems shows that these metal surfaces should be insensitive to small pH changes. The aqueous corrosion rates increase rapidly above pH 12 and below pH 4 for zinc and above pH 10 and below pH 1 for aluminum. The rates change very little in the intermediate ranges. We have measured the relative acidity of these surfaces after extended indoor exposures and find that they are mildly acidic, with aluminum surfaces being somewhat more acidic than zinc surfaces (1). Deposition of acidic substances would have to cause a substantial decrease in pH for the increased acidity to significantly alter the corrosion rate. For other metals, unless the small change occurs over a critical pH which is defined by a phase change in the Pourbaix diagram for the metal-water system, the effects on these metals are also likely to be small. Even if all the acidity that accumulated on these surfaces over 10 years remained active and contributed to a pH decline, the contribution of accumulated H 0 ions to urban indoor surfaces (estimated by assuming that most of the deposited acidity arrives on the surface as ammonium acid sulfate) is not likely to exceed 0.08 Mg/cm . The oxides on zinc and aluminum are good buffers and will tend to maintain the pH at a slightly acidic level. The thickness of oxide that would be required to dissolve in order to neutralize the acidity from ten years of accumulated ammonium acid sulfate is < 100 A. Further, some of the deposited acidity is likely to be neutralized by co-deposited calcium salts. On top-side horizontal surfaces, if all the calcium that deposits is assumed to behave like calcium +

3

2


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M A T E R I A L S D E G R A D A T I O N C A U S E D BY A C I D RAIN

carbonate, there would be more than sufficient basicity in the calcium salts to neutralize the ammonium acid sulfate. The acidity of dry deposition, then, is not likely to have a significant impact on zinc or aluminum degradation. The RH in most indoor environments is usually not above 70 percent and, thus, the CRH of most common metals is seldom exceeded. The time-of-wetness will be quite small. The corrosion rate is likely to be comparable to the outdoor rate (at similar contaminant levels) when the surfaces are dry. Such rates are insignificant compared to the wet rates for most metals 08). In many cases, the anions associated with deposited substances may play the dominant role in surface processes (24). The concentrations of sulfate, nitrate, and chloride, which accumulate on these surfaces, are likely to increase continuously. After 10 years exposure, total anion concentrations of five to ten Mg/cm can be expected in urban environments. These anions, especially chloride, are well known to dramatically affect the corrosion rates of many metals in aqueous solutions. This acceleration is often a result ol solubilization of the surface metal oxide through complexation of the metal by the anions. Chloride, in particular, can dramatically lower the RH above which a moisture film is present on the surface, since chloride salts often have low CRHs (e.g., zinc chloride - < 10 percent; calcium chloride - 30 percent; and aluminum chloride - 40 percent). The combination of the low CRHs of chloride salts and the well documented ability of dissolved chloride to break down metal oxide passivation set chloride apart from the other common anions in ability to corrode indoor metal surfaces. Some nitrate salts also have moderately low CRHs (e.g., zinc nitrate 38 percent; calcium nitrate - 49 percent; aluminum nitrate - 60 percent). The corrosion rate of most metal surfaces during dry conditions in outdoor environments has historically been considered to be insignificant and thus of little concern. Since the indoor environment is normally dry, corrosion rates indoors have also been considered to be insignificant for most metals relative to outdoor rates. While the accumulation rates can provide a framework in which degradation of metal surfaces may be considered, it is not possible to predict, directly, the corrosion rates. Nevertheless, the degree of degradation hazard associated with the various environments should follow readily from the calculated accumulation rates. Previously, the authors used measured accumulation rates of airborne substances at telephone company electronic switching equipment locations in cities across the United States to estimate the degree of hazard to the electronic equipment (0. The decreasing degree of hazard was as follows: New York City > Philadelphia > Albany > Cleveland, Houston > Colorado, San Francisco > Chicago, Seattle > Minneapolis, Omaha, North Jersey > Indianapolis > Lubbock > Wichita, Los Angeles, Orlando. The same ranking should be appropriate when considering degradation associated with other types of indoor materials. Consideration of the chemical and physical properties of these accumulated substances permits some further conclusions. The volatility of surface reaction products is likely to be important, as are the ambient concentrations of ammonia, carbon dioxide, and other gases that could influence the surface acidity. Indeed, the ratio of ammonium to sulfate that has been found on zinc and aluminum surfaces after extended exposures is much lower than typical ratios for ammonium to sulfate in airborne particles (4). Clearly, ammonium is able to volatilize from these surfaces through a hydrolysis reaction or, after redistribution of anions and cations on the surface such as


2

(NH )HS0 + NaCl -> NH C1 + NaHS0 4

4

4

4

through a reaction such as NH C1 — N H + HC1 4

3

We have also noted that chloride accumulation on indoor zinc or aluminum surfaces can occur at dramatically different rates (1). At locations where large differences are observed, hydrogen chloride has been implicated to be the source of much of the chloride accumulation. This difference in behavior was attributed, in part, to the slightly higher acidity and higher ammonium content of the aluminum surfaces, both of which will inhibit the reaction of hydrogen chloride with aluminum and will enhance the volatilization of hydrogen chloride.


14.



223

Conclusions The intent of this paper has been to provide a methodology by which the interaction of the environment with indoor surfaces can be related to prevailing outdoor concentrations of airborne substances. The complexity of the combined effects of these airborne substances frustrates making quantitative predictions of the degree of degradation. The relative degree of hazard for the different environments can be estimated from the methodology and, based on previous experience with zinc and aluminum surfaces in known environments, provides a framework for qualitative rankings of comparable environments.


Literature Cited

1. Sinclair, J. D., Psota-Kelty, L. Α., Proceedings of the International Congress on Metallic Corrosion, 1984, Vol. 2, pp. 296-303. 2. Hansen, D. Α., Hidy, G. M., Atmos. Environ., 1982, 16, 2107-2126. 3. Pruppacher, H. R., Klett, J. D., "Microphysics of Clouds and Precipitation," D. Reidel Publishing Co., Holland, 1978. 4. Sinclair, J. D., Psota-Kelty, L. Α., and Weschler, C.J.,Atmos. Environ., 1985, 19, 315323. 5. Prospero, J. M., Savoie, D. L., Nees, R. T., Duce, R. Α., Uematsu, M., and Merrill, J. M., SEAREX Newsletter, 1982, 5(2), 19-21. 6. Kleinman, M. T., Tomczyk, C., Leaderer, B. P. and Tanner, R. L., Ann. NY Acad. Sci., 1979, 322, 115-123. 7. Rahn, Κ. Α., Borys, R. D., Butler, Ε. L. and Duce, R. Α., Ann. NY Acad. Sci., 1979, 322, 143-151. Matusca, P., Schwarz, B. and Bachman, K., Atmos. Environ., 1984, 18, 1667-1675. 8. Graedel, T. E. and Weschler, C.J.,Revs. Geophys. and Space Phys., 1981, 19, 505-539. 9. Graedel, T. E., "Chemical Compounds in the Atmosphere," Academic Press, New York, 1978. 10. Logan, J. Α., Prather, M. J., Wofsy, S. C., and McElroy, M. B., Geophs. Res., 1981, 86, 7210-7254. 11. Huebert, B. J. and Lazrus, A. L., J. Geophys. Res., 1980, 85, 7337-7344. 12. Tanner, R. L., Ann. NY Acad. Sci., 1980, 338, 39-49. 13. Total chloride (fine and coarse mode) background concentration was 0.12µg/m ;fine mode backgroun concentration was 0.12 µg/m (see Reference 9). 14. Yocum, J. E., J. Air Polln. Contr. Assoc., 1982, 32, 500-520. 15. Rice, D. W., Cappell, R.J.,Kinsolving, W. and Laskowski, J. J., J. Electrochem. Soc., 1980, 127, 891-901. 16. Pruppacher, H. R., Semonin, R. G., Slinn, W. G. N., Proceedings of the Fourth International Conference on Precipitation Scavenging, Dry Deposition, and Resuspension, 1982, Vol. 2. 17. Suzuki, I., Hisamatsu, Y., Masuko, N., J. Electrochem. Soc, 1980, 127, 2210-2215. 18. Dean, S. W. and Rhea, E. C., Atmospheric Corrosion of Metals, ASTM Special Technical Publication 767, May, 1980. 19. Vernon, W. H. J., Trans. Faraday Soc., 1935, 31, 1668. 20. Ailor, W. H., Atmospheric Corrosion, The Corrosion Monograh Series, 1982, p. 139. 21. Rice, D. W., Phipps, P. B. P., Tremoureux, R.,J.Electrochem. Soc., 1980, 127, 563-568. 22. Proceedings of the International Congress Metallic Corrosion, 1984, Volume 1, pp. 79 143, 274-332; ibid, Volume 2 pp. 99-179; ibid, Volume 3, pp. 394-467; ibid, Volume 4, pp. 506-550. 23. Pourbaix, M., "Atlas of Electrochemical Equilibria in Aqueous Solutions," translated from French by J. A. Franklin, National Association of Corrosion Engineers, Houston, Texas. 24. Proceedings of the International Congress on Metallic Corrosion, 1984, Volume 1, pp. 208-240; ibid, Volume 2, pp. 296-316; ibid, Volume 3, pp. 192-228. 25. Rahn, Κ. Α., "The Chemical Composition of the Atmospheric Aeorosol," Technical Report, Graduate School of Oceanography, University of Rhode Island, Kingston, Rhode Island, 1976. 3

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Effects of Acid Rain on Indoor Zinc and Aluminum Surfaces - ACS

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