2.1-Assessmeent tools

A- The models of long-range atmospheric diffusion

For the sake of determination of the consequences of emitted of pollutants from various sources in a few kilometers distances, the models of some long-range atmospheric diffusion have been formulated. In many cases, the air pollution of a country affects the neighboring countries. These models are not of complete validity.

Puff model is used to long-range atmospheric diffusions. In this model, emission is always considered with a series of puff which is carried around by variable wind-field with the use of puffs instead of plume, wind direction changes are model easier Observed winds are usually used and then is interpolated into other regions through measurement of (distance)^-2 .

The following puff model has been regulated on the basis of Gaussian model.

(1)

Q= diffusion mass rate

d x, d y, d z= diffusion parameters respectably in x , y, z axises direction

C= pollutant concentration (qm/m³)

H=final plume ascend

It is necessary to be noted that all the models, restrict the pollutants to mixing depth and in long-range transfer in a distance about 100 kilometers, pollutants are distributed in mixture layer in the homogeneous from, so in order to calculation the information about the mixing depth of region is necessary.

With regard to emission parameter (d ) firstly about puff, d x=d y it is supposed, but d 2 , d y for the similar puff of plume is not continuous.

Batchelor ( 1952) suggested d_y(puff) a x ^3/2-, d_y(plume) a x but actually when using equation (1) d puff, plume are equaled, In many distances, Wendell( 1976) interpolates Pasquill and Gifford’s d_y , d_z curves.

Hefter (1980) uses the experimental relation d y=0.5 t (d y owing to meter and t owing to second).

While Johnson supposes that Fickain Law d y=2k.t- if ( k_? @ 10⁴m².s^-1) , is valid. It is obvious that d y for one day or more averages is not of great importance. Because the total diffusion is governed by the fluctuations of large- scale wind direction in large averaging times.

The other puff model presented by Suttan, (1932) that may be used to determine the concentration down wind from one source in H height.

(2)

t= The time after emission or transfer (second)

It should be noted that dispersion parameters, relates to dispersion statistical section and d x is standard deviation of concentration distribution in puff and down wind (Moreover down wind , by wind no dilution takes places.) Mainly the speed of wind may be used to present the situation down wind of puff center. This speed may affect the dispersion, indirectly because the diffusion and dispersion parameter of d x, d y, d z…. may be function to wind speed. d y and d z have been presented in table 1, but there is less information above d x.

On the whole, the amount of d x may be used like d y.

The primary dimensions of puff, for instance distance from the nuclear explosion place, may take place through a figurative distance.

Another form of Gaussion puff equation have been demonstrated in the form of relation on the basis of constant of proportionality k, that is xo=yo=0 & zo=H (In high frequency transfers H can be the average of the depth of mixture)
 
 

(3)

t= Emission time (second)

D t= The time of emission continuity (second) which is considered less.

U= The average wind speed (m/sec).

Since, in high frequency transfer , after 100 kilometers, pollutants in mixture layer with L depth appears in any point of this layer can be calculated from the following relation :

(4)

In high Frequency dispersion and transfer models , removal is very important, because the half life of pollutants like sulfur dioxide in dry and wet deposit and chemical transformations is typically for a few days.

It is presumed that the deposit rate (V_d) for sulfur dioxide is supposed 1 cm/s (Shoih, 1977) and 0.8 cm/s (Johnson, et al. 1978) has been considered.

The conversion of sulfur dioxide to sulfate about 1% per hour is presumed. (Jonson et al,1978).

It is presumed that the wet removal rate to be proportional with rain speed. For example, l =10⁴ R ½ (removal section in second) that R is the rain speed according to millimeter per hour. Another formula with little difference was suggested in the form of l =0.6×10⁴ . R

When it rains, removal is completely effective , but in the long term it has been obvious that wet & dry removal have been equally effective.

Nitrogen oxidation into nitrogen dioxide and then nitrogen pent oxide and its reaction with water vapor produces nitric acid.

The rate constant of removal reaction of nitrogen dioxide is about 4×10⁷ cm³/mol.s.

The rate of disappearance is presented according to rate law for first class factorization

(5)

with integration appears as follows:

that K is rate constant of decomposition whose dimension is (time)^-1.

With regard to nuclear decomposition K is independent of temperature and other chemical substances and etc. If the time is considered for half life of existed substance for disappearance, we will have the following relation:

(6)

that with putting amount K of 4 relation in 3 relation, we will have :

Decay Factor = D.F.=  (7)

that : U= Wind speed (m/sec)

t= Time of emission or transfer ( second)

T 1.2 = Half life of removed substance ( second)

X= The distance of emission or transfer (m)

Co= Primary concentration

C= Concentration in t time or x distance.

Thus for the determination of concentration of any pollutant in each point, in high frequency transfer, calculated concentration through " Puff" presented formula should be multiplied by decomposition coefficient.

With multiplication of decomposition coefficient in 4 relation, concentration is calculated in each point of mixing depth.

(8)

To determine deposit flux, deposit rate (V_d) should be multiplied in pollutant concentration that in such case we will have:

(9)

F= Deposit flux according to mass unit on surface unit ´ unit time.

B- Requirements

With regard to the above suggested models, following requirements for the locating of models are put forward.

1. Liable d x, d y, d z
2. Monthly average of speed & direction and frequency of local wind, percent of region steadiness.
3. Monthly average of mixture depth.
4. Monthly average of rain fall
5. Half life of pollutants
6. The wet & dry deposit rate of pollutants
7. Monitoring network establishment for the survey of model results connection and measurement, laboratory and sampling tools
8. An equipped computerized system, a series of the recent researches in the field of modeling of long-rang diffusion

2.2.1 Introduction

World attention was first drawn to the problem of "acid rain" in 1972 when Sweden and Norway reported their concern about this phenomenon. From these Scandinavian studies, scientists in many other countries became increasingly aware that there might be effects on the "receiving" aquatic ecosystems, caused by the transport and deposition of air pollutants.

Deposition of acidic materials may occur through either wet and/or dry processes Deposition velocity varies widely but, using a value of 0.5 to 1 cm sec ^–1 , 5µgm^-3, SO₂ is equivalent to 1,000 mm rain at pH 403 to 604

Although the relative importance of each process is still not fully known, modeling and mass balance studies indicate that wet and dry depositions of sulfur compounds are of equal importance in northern Europe and North America. While in remote areas distant from sources dry deposition of sulfur seems to be of lesser importance, it has been concluded that dry deposition is relatively more important than wet depositions in areas like the Ohio valley- close to major emission sources.

The acidity of the precipitation is determined by the hydronium ion concentration (H⁺ for short) and is usually given in term of pH = -log(h⁺ conc. ). The term acid precipitation is often used for precipitation with pH below 5.6, which is the pH of pure water in equilibrium with atmospheric carbon dioxide. Even before anthropogenic emissions became important, the acidity of the precipitation was certainly affected by many compounds besides CO₂.

The natural pH was probably usually in the range 5 to 6, but values outside this range were also likely to occur in some areas[9]. Precipitation over large regions is at present acidic, with annual average pH values of about 4.1 to 4.3 (corresponding to a H⁺ concentration of 80 to 50 µeq/1)

The pH of precipitation is a function of the presence of H⁺ in association with SO₄^-2 , NO₃^-, NH₄⁺ and CO₂ (see table 1). In addition, concentrations of various heavy metals and organic micro pollutants are also usually elevated in the precipitation presently experienced over large areas of North America and Europe by comparison with levels in remote regions.

The seasonal pattern and quality of precipitation are also important for determining the potential for acidic deposition impacts on the environment. Acid pollutants accumulating in the snow pack have a higher potential for causing deleterious effects on the aquatic ecosystem in areas with higher amounts of snowfall than in areas with lower amounts of snow accumulation. The effect is due to the rapid flushing of accumulated acid during periods of snowmelt.

Both we and dry depositions undergo chemical alteration on contact with vegetation both on the surface or indirectly within cellular tissue. The nature of the leachate or throughfall depends upon a great many factors including plant characteristics, land characteristics, site conditions and climate. Generalizations are, therefore, difficult because of the wide range of environmental conditions. There is also considerable variability in the degree to which elements are susceptible to leaching and the degree to which various plant parts can be leached.
 
 

Annul mean concentrations (µeg/1) of major ions in precipitation
	Southern  Sweden a/	Birkenes, Southernmost Norway b/	Kejimkujik, Southern Nova Scotia Canada c/	Karvatn, Northern Norway d/
H+	52	69	24	17
SO42-	70	71	28.4	12
NO3-	31	41	12.4	5
NH4+	31	42	4.4	6
Na+	15	53	35.7	41
Ca+	14	9	6.5	5
Mg2+	8	12	7.9	9
K+	3	3	1.6
Cl--	18	63	40.6	46

a/ Typical composition for precipitation in southern Sweden in the mid-1970s.

A few essential points with respect to effects of vegetation and ion exchange are illustrated in figure 1. Here it is indicated that the roots take up various cations and release H+. The cations are returned to the soil by natured processes if plant matter is not accumulated or removed. Cation exchange in soil is one of the most important processes to consider. Soil particles normally have a negatively charged surface and, thus, a layer of cations close to the surface. These cations may be interchanged with those in the solution. Cation exchange may increase or decrease the concentration of H+ in the runoff; and when a dilute solution of neutral salts percolates through acid soils, the leachate becomes acid because of exchange of other cations with hydrogen ions. It follows that the acidity of runoff depends on the acidity of the soil and the ion content of the deposition as well as on the degree of contact between water and soil.

Due to the requirement for charge balance in the soil solution, soil cation leaching is highly dependent upon the mobility of the anion associated with the acid- whether it be SO₄²- , NO₃-, HCO3-, or an organic anion. Because of the N-limited status of many forests, most NO3- is assimilated by plants during the growing season, thereby not contributing to cation leaching.

Because during the growing season, thereby not contributing to cation leaching. During snowmelt or after rainfall, NO3- may be released but in mist areas the concentrations in runoff are 10w compared with SO₄^2- concentration.

Weathering of most minerals leads to consumption of H+ - ions (quartz is an exception). The H⁺ -ions in solution are replaced by the other cations such as Ca²⁺, Mg²⁺, Na⁺ and K⁺. Carbonic acid is a very important weathering agent.

Sulfur, like nitrogen, is an essential plant nutrient, but it is usually in adequate supply for plant growth in soils. In spite of the many possible reactions, much of the SO2 and SO4^2- deposited in acidic deposition is not retained in soils, and SO4^2- is often the anion balancing the presence of H⁺ and other cations in surface water and shallow ground water. The amount of SO4²⁺ in runoff from the Canadian shield is very close to the amount deposited . Fairly close agreement between S deposition and output has been reported for Norwegian catchments when a correction factor based on equality of chloride input and output is applied .

In some catchments, with soils (chiefly those rich in Fe and Al sesquioxides) sulfate may be retained by absorption processes. Sulfate ions can be reduced to sulfide mainly by bacterial action- an action which consumes acid and raises the pH of the soil drainage water.

Nitrate ions (NO3^-) can be incorporated directly by vegetation resulting in the release of hydroxyl ions (OH^-) and thus exerting a neutralizing effect in soil systems. In contrast, ammonium is a source of hydrogen ions when it is used by plants, and is nitrified by bacteria thus producing H⁺ . This release of H⁺ could be a significant source of acidification in poorly buffered soils and amounts, no net release of H⁺ of bicarbonate occurs.

It is generally believed that the two most important sources of H⁺ acting in natural soil systems are organic and carbonic acids. Humus material produces new exchange surfaces at intermediate stages of decomposition. Provided these are not occupied by base cations, this represents H⁺ which can exchange with other cations moving through the soil system[19].

Although these organic acids may contribute to low pH values (>5) in soft water lakes, there is no evidence that recent regional acidification has been caused by such compounds. Synoptic surveys of acidic clear water lakes have concentrated on lakes which have relatively low or no water color, and thus low dissolved organic content, low organic acid content, and low organic anion concentration. Ion balance are achieved largely using H⁺ , major cations sulfate and chloride for lakes with a pH below about 5.5 where HCO3^- becomes relatively unimportant.

A further effect of acidic deposition or soil acidification is an increased solubilization of metals in the soil leachate. Increased concentrations of Al, Mn and Zn in soil water can occur without increased atmospheric loadings. Higher concentrations of these metals result from an increase in solubility at lower pH levels. While Al ordinarily is leached from the upper soil horizon of podsol soils by carbonic acid, tannic and humic acids and organic chelation, it is usually deposited in lower soil horizons. Under the influence of strong acids in deposition, aluminium may be mobilized or transported by saturated flow through the surface layers into lakes and streams. The elevated concentrations of aluminium and manganese in acidic surface waters thus reflect the deposition of anions, the capacity of soil cation exchange and flow conditions. Acidic deposition and soil acidification may thus result in the additional release of aluminium.

All of the foregoing processes take place in a dynamic hydrologic system. This system is far from uniform, and water moving through natural soils involves differing rates of capillary and gravitational action; also, some moisture flow may be directed overland or channelled through portions of the soil profile in root channels, reducing the opportunity for soil/water interaction. In addition, a stony soil can concentrate leaching effects within a smaller soil volume than a non- stony soil. Thus, theoretical calculations must always take into account specific in situ conditions.

2.2.2 Effects of acid inputs on water chemistry

Acidification of waters may be defined as the decrease in acid neutralizing capacity (ANC). Long-term acidification implies a continuing loss of ANC measured over a period of years. Short- term or episodic acidification implies a reversible loss of ANC over periods of days or weeks. (Humic waters where acidity is governed by organic acids are not included). Water alkalinity is principally derived from reactions with the surrounding soils. In areas of little atmospheric sulfur load, a very close relationship (1:1) normally exists between total leached cations ( mainly excess Ca + Mg) and alkalinity. Lakes of this type have a low sulfate concentration.

Inputs from sulfur deposition may acidity the runoff water if the soil neutralizing capacity is inadequate. The runoff water normally has a higher pH than precipitation, as well as higher levels of calcium, magnesium and aluminium which accompany the anions. Of these, sulfate is normally of greatest importance.

2.2.3 Relation between sulfur deposition and PH in fresh water

The " mobile anion concept" is useful when discussing the effects of changed deposition on the chemistry of freshwater. In most Scandinavian and North American catchments studied, the nitrate, ammonium and potassium concentrations are generally small in runoff, although nitrate does in some cases increase during snowmelt and after heavy rain. Usually Na and Cl^- are nearly equivalent and are generally ignored. In systems with low bicarbonate concentrations, the importance of sulfate for the transport of cations through soils, including H⁺ and Al-ions, is then evident .

The shift in pH in lakes or streams resulting from a change in sulfate concentration varies with the type of catchment and the sulfur deposition. At one extreme in catchments with easily weatherable material , changes in the sulfur deposition within reasonable limits (say, a factor of ten) probably do not lead to significant pH shifts in lakes and streams. At the other extreme may be an area where an increase in sulfate concentrations in runoff is matched by a similar increase in H⁺( or rather H⁺ + Al- ions ), with negligible change in the concentrations of other cations such as Ca²⁺.

2.2.4 Effects of water acidification on biotic components

As the pH of surface waters declines, effects on biota are noted. As most organism have a specific pH-tolerance range, it is obvious that an organism will disappear from the system if pH exceeds this range. Beside these direct effects, indirect effects usually occur due to water chemistry changes other than pH or changes in interspecific relationships. The most conspicuous difference between acid aquatic systems and systems having a normal pH is the greatly reduced diversity of taxa in acid waters.

2.2.5 Effects on micro- organisms

Decomposition of leaf litter has been shown to decrease in acid waters, while a shift is being observed from bacterial to fungal decomposition [42]. However, experimental studies on decomposition in lake sediments are inconclusive. Reduce decomposition will lead to reduced nutrient cycling and, consequently, to changes in the entire food chain of ecosystems.

2.2.6 Effects on plants

Species diversity of algae is usually reduced in acid water[44]; but some exceptions have been observed[45]. Primary production, however, is not diminished, except in those cases where available phosphate is low .

Acid lakes are often characterized by increased growth of benthic filamentous algae ( mainly Zygnema spp. Zygogonium spp. and Mougeota spp. ) forming dense mats and thus possibly reducing light availability to macrophytes. On the other hand, chrysophytes and diatoms usually decline, and acid lakes are often dominated by dinoflagellates . Diatom assemblages can be used to estimate pH values with reasonable accuracy ( to 0.3-0.5 unit ). In the Netherlands, a number of pools have greatly changed diatom spectra when comparison is made with old samples taken around 1920, indicating a change in pH from a wide range of 4 to 6 to a narrow range of 3.7 to 4.6. In some pools only one acidobiotic species, Eunotia exigua, survives .

Information on the effects on macrophytes is scarce. Grahn et al. have reported a suppression of isoetid- dominated vegetation by luxurious sphagnum growth. In other instances isoetid vegetation is suppressed by Juncus bulbosus. In the Netherlands isoetid vegetaion, usually dominated by Littorella iniflora, is absent or dwindling in 78 percent of the stands known around 1950, in most cases being replaced by Juncus bulbosus or sphagnum- dominated vegetation. As the mean water pH for littorella-dominated vegetation is around 6.5 compared with 3.9 for Juncus and 3.8 for sphagnom- dominated systems, this indicates drastic changes in pH for these waters . The capacity of sphagnum to exchange H⁺ for cations will lead to lower pH, calcium, aluminium and iron in the waters.
 
 

2.2.7 Effects on aquatic macro-invertebrates

Numerous aquatic macro-invertebrates are known to be susceptible to water acidification. Evidence indicates that molluscs in general are highly sensitive. According to Okland[56], no snails are found at pH-values below 5.6 and only a few species can tolerate pH levels below 6. A greater correlation of snail species diversity has been found with hardness and geology, than with pH, although with the same level of calcium both number of species and time- catch abundance decrease with decreasing pH.

Crustaceans are absent from acid waters: Gammarus lacustris is not found below pH 6 and Asellus aquaticus becomes very rare below pH 5.2. Freshwater crayfish species are sensitive to low pH while moulting, calcium uptake being inhibited at pH<5.3 .

Insects differ greatly in sensitivity. The diversity of the macro-invertebrate community is usually much smaller in acid waters: Friberg et al. found 46 taxa of benthic invertebrate fauna in a non-acid stream (pH 6.5 to 7.3) and 18 taxa in an acid stream (pH 4.3 to 5.9) with lower conductivity and calcium.

2.2.8 Effect on amphibians

Most amphibians are highly sensitive to acid water, especially with regard to reproduction, although there are substantial differences in the sensitivity of different species. Reduced breeding success and reduced populations of yellow- spotted salamander (Ambystoma maculatum) were reported in meltwater pools with pH<6 while another species (Ambystoma jeffersonium) can breed at pH 4.8.

Strijbosch reported a correlation between H⁺ - concentration and percentages of dead and moulded egg masses of frogs and toads in the Netherlands. Most species of amphibians are not found or are rare at pH values below 5. In Canada, as several amphibian species breed exclusively in meltwater ponds, these species are threatened with extinction because of the reduced pH of many ponds of this type.

To predict the fishery status of any lake’s pH, this approach was used by Brown and Sadler[36] and Muniz and Seip on the basis of data published by Wright and Snekvik and Sevaldrud and Muniz. The first data set comprised 700 lakes; Sevaldrud and Muniz extended the study to 3,725 lakes in the counties of Qstfold, Telemark, Aust-Agder, Vest-Agder and Rogaland(Norway), including those of wright and snekvik. Water of many, but not all, of the lakes was sampled once for pH and other water quality and fish status was judged from interviews and qusetionnaires as "lost", "sparse", "good" , or "never had fish", for about 3,400 lakes.

2.2.9 Effects of acid water on fish

Although there is a reasonable correlation between pH and fish status in southern Norwegian lakes, there is a better correlation with calcium, and no correlation with sulfate or with total aluminium. However, aluminium is higher in lakes and streams with lower pH. While the relative importance of pH, calcium and aluminium is not understood, there is general agreement on the effects of acid water on fish. One report noted that:

Lake	%Fishless		NO3- + ex SO42- -m eg/1	C.R	Attitude	Ca2+	Al	H+	H+/Ca2+
Set	a/	B/			m	m eg/1	m eg/1	m eg/1	-
1	67	89	54	0.54	632	20	142	24	1.20
2	50	65	71	0.68	508	30	174	22	0.73
3	36	55	77	0.77	434	38	190	18	0.74
4	24	35	93	0.78	310	57	182	12	0.13
5	9	9	128	0.96	200	118	130	4	0.03

Note: C.R. (catchment reactivity ) is defined as 1- 

a/ Wright and Snekvik 1977 (data are from this source)

b/ Sevaldrud and Muniz 1980
 
 

Species	Acute pH exposure		Long-term pH exposure		Comments
	Adult LC50	Juvenile LC50	Critical pH for Reproduction	Critical pH for Egg hatch
Salmo sa]ar	-	Eggs4.0-4.5 Alevins 4.0 4.3 fry<4.0<4.5	Not known	>3.3(hard- water) 5-5.5 (soft water)	Lowest pH at which adult Fish found is pH4.6[73].
Salmo gairdneri	1+fish,3.4-4.5	Fry 4.0-4.5	Not known	4.7,hatch 50% (soft water)	Infinite survival at pH 5.4.  Survival in stocked lakes at pH 4.7-5.5 Reduced growth at pH 4.6. Generally acknowledged most sensitive species.

 

Table 4: Biological changes observed early in the acidification of lake 223 with sulfuric acid and the approximate pH at which they occurred
 

PH
Below 6.5	Increased sulfate reduction Increased abundance of chlorophyta Decreased abundance chrysophyta	Schindler et al., 1980 Findlay and Seasura, 1980 Muller, 1980
5.8 - 6.0	Disappearance of Mysis relicta Disappearance of Plimephales promelas	Nero, 1981 k. Mills,  unpublished data
5.6	Increased embreyonic mortality in  Salvelinus namaycush Reduced calcification of Orconectes virilis exoskeleton begins	Kennedy, 1980 Malley, 1980
5.3 – 5.4	Increased infestations of orconectes Virilis with thelohania sp. Epidemics of Mougetea in littoral zone Decline in Orconectes populations	R.France, unpublished data I. Davies, unpublished Data

 

A maximum concentration of 25 µg SO₂/m³ as an annual average has been recommended (IUFRO,1978 , and further confirmed in 1982) to maintain full protection of spruce forests in higher regions of mountains , and in boreal zones.

2.2.10 Mechanisms of atmospheric corrosion

The mechanism of atmospheric corrosion is dependent on the material involved, atmospheric meteorological conditions and pollutants present. For metals the process is electrochemical in nature, requiring a film of moisture.

In practice, this results in a discontinuous process and means that the time during which a moisture film is present on the surface is a major factor in the final corrosion rate observed. Apart from the pollution level there are many parameters which influence the final corrosion rate including relative humidity, temperature, rainfall, wind speed and local topography of the site, in addition to the physical characteristics of the exposed material such as shape and heat capacity .

Particulates, acid smuts and sulfates may promote corrosion by : direct chemical action on the metal or corrosion product; providing active sites for moisture condensation on the surface; and acting as an adsorption site for air pollutants. Ammonium sulfates are known to accelerate corrosion by reducing the critical humidity and providing sulfate ions.

Deposition rates and concentrations of sulfates are known to be low compared to those of SO₂ . Atmospheric corrosion surveys have shown only weak correlations between sulfate particulates and corrosion rates.

It has been shown in laboratory studies that below the critical pH of 3 to 4 the corrosion rate of carbon steel, zinc, copper and aluminium increases. In outdoor exposure, some field studies have demonstrated that the final effect of rain acidity depends on amount, duration, pH level and washing effect of the rain .

The pollution level and time of wetness are the most important factors in the process of atmospheric corrosion of metals and metallic coatings.

Efforts aimed at clarifying the physico- chemical background of the process have helped in finding a basis for its kinetic interpretation. Interpretation is limited, however, to isolated periods of the process and it is difficult to use them in any technical prediction of the long-term course of atmospheric corrosion. For this purpose, results of research and field tests of an empirical character in different atmospheres can be used and correctly treated mathematically. In this way, many dose/response relationships can be obtained, and the due significance of these relationships is sufficient for technical applications to be made. But the results of these efforts are not yet suitable for generalization and technical utilization at the international level.

The corrosion rate of carbon steel has been studied in several investigations on both a national and an international basis. In the above- mentioned studies, considerably higher corrosion rates of carbon steel were found in urban and industrial atmospheres than in rural atmospheres.

For sulfur emissions from a point source, such as an industrial plant, the corrosivity of the atmosphere is locally high but quickly decreases according to distance from the source. This indicates that atmospheric corrosion is usually a local problem, but in densely- populated and highly- industrialized areas it may be a regional problem.
 

Reference		Survey details			Significant Parameters		Equations
Sereda 1960 [41]	T SO2 tw 2 sites 8 months pbO2 method		Monthly exposures Rate mg/dm2/day Of wetness SO2mg SO2/dm2/day	T SO2 assumed meteor conditions to be constant		Y= 0.131x+0.180z+0.787 Y= log corr. Tate mg /dm2/d X= SO2 mg/dm2/d Z= temperature of during wetness (monthly av. )
Cuttman and Sereda 1968 [35]	7 sites `, 12 , 18 months tw panel T, ambient T, SO2, cl		Steel Zinc Cu	Tw SO2		Z=0.16 tw 0.7 (SO2+ 1.78)
Haynie  and Upham 1971 [17]	6 sites SO2 No NO2 CO H/C, oxidant, weather particulate		Steel 3 types	SO2 t oxidant		y= 9.013(e0.0016so2)(4.768t)0.7012- 0.00582ox) different equations for each steel

 

SO2 deposition rate (mg SO2/ m2 per day)	Category of Location	Category of corrosion aggressivity a/	Steady state  corrosion rate b/ (µm/year)	Corrosion losses after 10 years (µm)
<20	Indoor	1	~1	<1
20 to 60	Sheltered	2	1 to 5	<10
<20	Outdoor	3	5 to 10	<150
20 to 60	Outdoor	4	10 to 30	<350
>110	Outdoor	5	30 to 60	<600

a/ atmospheric corrosion of metals in corrosion aggressivity categories 1 and 2 has a probability character, and obtainable corrosion losses are lower than in categories 3 to 5.

b/ Corrosion losses within 10 years also include corrosion in the initial period before the steady state corrosion rate has been obtained.

Type of atmosphere	Test site	Corrosion rate(µm/year)
Industrial	Usti Nad Labem (Czechoslovakia) Most (Czechoslovakia) Aubervilliers (France)	5.0 4.0 6.0
Urban	Moscow (USSR) Prague (Czechoslovakia) Stockholm (Sweden) St. Denis (France)	1.7 2.0 2.5 3.7
Rural	Erken (Sweden) Zvenigorod(USSR) Picherande(France) Kasperske Hory (Czechoslovakia)	0.8 0.9 0.6 1.0

 

Reference	Equation	parameters
Barton 1980 [39] 10yaear extrapolation Zinc	K= 0.00076t w 0.50SO2 0.718 K1 = 1.4tw 0.51SO2 0.72	tw= total time RH>80% t> O0 c in term Of hrs/day calc. From linear reg. average SO2 daily averages (4 x day x 1 x week) K = corrosion loss or rate g/m2/day
Haynie & Upham  1970[32] Zinc	K= 0.001028 (RH-48.8)SO2	Av. SO2 K = corrosion rate =µm/exposure time

a/ High corrosion rates usually occur in areas with heavy dust deposition

When sulfur compounds are absorbed on surfaces, a series of reactions begins with gypsum (Calcium sulfate ) as the end product. Gypsum, which is more soluble than calcium carbonate, is then washed away by rain. Other factors which may cause deterioration are the increase in volume that takes place when calcium carbonate reacts to form gypsum, and variations in temperature .

Biological weathering has been suggested as a major contributor to deterioration. Bacteria on the surface draw SO₂ from the atmosphere; the microbes’ metabolic system converts the gas into sulfuric acid which then attacks the calcium carbonate in the limestone , marble and sandstone , liberates carbon dioxide and the microbe nutrient, and finally produces calcium sulfate as a by- product. Other studies have claimed that all deterioration can be attributed to chemical and physical (mechanical) processes, and that biological aggression is negligible.

Evidence that air pollutants attack concrete has not yet been sufficiently documented; however, the likelihood of such an occurrence is suspected since cement contains substances that may react with acid pollutants. It is generally considered that the main deterioration of concrete results from carbonation from CO₂ or from attack of reinforcement by chlorides. Calcium aluminates contained in cement converts in the presence of sulfur compounds into ettringite which in large volumes can cause cracks in concrete; however, high sulfate concentrations are required for any such attack to occur; and at normal atmospheric levels of SO₂ attack would be limited to the surface skin.
 
 

Sengupta and de Gast(1972) Laboratory study	Sulfate formed(g)= 0.05 (porosity ) + 0.07 (permeability) + 0.04 (water absorption ) + 0.07 (Calcite/Dolomite) +0.32
Haynie Spence and Upham (1976) Laboratory study	Y=3.31+0.78H+2.95.10-3SO2+3.33.10-3O3 y=µm/year H= RH% SO2 =(µg/m3) O3 =(µg/m3)

Paints contains both pigment and vehicle. Together they enhance the attractiveness of a surface and protects the underlying material from corrosion and weathering. Air pollutants may counteract both of these functions by increasing the erosion of the protective coating and by hastening the corrosion of the underlying surface. The latter process them weakens the adhesive properties of the paint and shortens the life of the paint. It should be mentioned that, when painting and / or repainting is carried out in sulfur- polluted atmospheres , the deposition of pollutants on the surfaces in the time between surface preparation and painting may play an important role in shortening the adhesive property of the paint.

Several authors have demonstrated that length of life of paint coatings is related to pollution of the atmosphere. There are many different types of paint and these have a multitude of formulations for both pigment and vehicle. It is considered that the pollution level probably affects the length of life of various paints in different ways. Studies indicate that the most important potential effects of SO₂ on paints are interference with the drying process, penetration of the paint film, and acceleration of the normal erosion process. Other factors known to degrade paints are H₂S sulfates and other particulates, O₃ and wetness.

Data are available concerning aging, degradation, cracking, loss of reflective qualities, etc. of plastics, rubbers and similar products; however, no valid damage function or dose/response relationship is known. Outdoor exposure of these materials usually leads to a decrease in physical properties and adversely affects the material from an aestetic point of view.

Haynie et al 1976
Laboratory study
1- Oil base house paint on aluminium	Y=14.3+0151SO2+0.388H	Y=(µm/year) NO2 increased the weight  SO2 (µm /m3 ) of the film H=RH% O3 Was not significant
2- Viny1 coil coated paint	Y=2.51+1.6 10-5(SO2)(H)

• Painted woodwork is affected by sulfur pollution butits influence on modern paints is only slight, and experimental data are influence to quantify the effects.
• Paper and leather have been damaged when subjected to long-term exposure in indoor environments in SO₂ polluted area .
• Textiles made of both natural and synthetic fibers have been reported to be detrimentally affected by S-pollutants. At present, experimental data seem insufficient to quantify the effects or to assess their economic significance.
• Air pollution by sulfur compounds is considered to be the most important parameter increasing the rate of deterioration of a number of objects of great historical and cultural value (e.g. frescoes, bronze statues, etc.). Opinion is still divided on the role of SO₂ in the deterioration of medieval stained glass windows.

• Electrical devices, particularly those containing copper, silver and gold contacts, increasingly fail in polluted areas, where high deposits of sulfates , chlorides and nitrates have been found on metal surfaces . Corrosion is probably due to a synergistic effect of H₂S , SO₂ , No_x , sulfates and chlorides and it is not yet possible to estimate the extent of corrosion attributable to the presence of sulfur compounds. Experience with electric insulator breakdowns in the United Kingdom attributes the damage to particulate and marine salt fogs.
• Automobiles are exposed to a complex influence of environmental factors; road mud and de-icing salts should , in particular, be mentioned. Statistics indicate that cars used in urban areas have a shorter life than those used in rural areas. Because of the complexity of the problem, it does not appear possible to isolate the effects of sulfur pollutants.
• Steel structures used in the open air have to be protected against corrosion. When a protective system for a given lifetime is to be chosen, the corrosivity of the atmosphere is a decisive factor. It is then necessary to select better and more expensive protective measures in polluted atmospheres.

Country	Study	Damage function	Corrosion and metal protection costs
Norway	1979 Henriksen et al.	Y=0.45 SO2 + 0.7 (galvanized steel) L1= 11.7 – 0.042 (SO2) (painted steel) Cost saving for 40% SO2 reduction is " " " SO2 = 0  L = life of paint layer	989 million kroner (1979) 15.7 million kroner (1979 ) 77.7 million korner (1979)

 

2.2.12 Effect of sulfur compounds and other related air pollutants on health

The aim of this report is to consider some of the currently acceptable published evidence of the relation between health effect and air pollution due to sulfur compounds , particulates and nitrogen oxides.

There are a number of sulfur compounds that need to be considered in relation to their health effects. Sulfur oxides found in air, as a result of human activity , originate in compounds present in many coals and heavy oils. The main point sources of sulfur compounds are emissions from power stations and industry, although domestic sources may also be important ; because of the relatively low level of emission, the latter can in some circumstances have a disproportionate effect on concentrations in urban areas. Sulfur dioxide is the main oxide formed, although some of the sulfur in the fuels may be further oxidized during combustion to sulfur trioxide. Some sulfur in coal may remain in the ash. Sulfur dioxide released to air can be oxidized to from sulfuric acid and, through reactions with other pollutants, sulfates.

Oxides of nitrogen form a further group of gaseous air pollutants of possible concern in relation to health. They are produced on combustion from nitrogenous components of some materials such as tobacco or more commonly from the fixation of atmospheric nitrogen. The two most abundant forms of nitrogen oxides as pollutants of urban air are the gases nitric oxide and nitrogen dioxide. Nitric oxide is converted to nitrogen dioxide (though only slowly at high dilution) and thus is a precursor of the latter. Nitrogen oxides are formed when nitrogen and oxygen come in contact with a hot surface. They may be formed naturally during volcanic eruptions or by lightning or be man- made during the manufacture or detonation of trinitrotoluene, the burning of tobacco or from any combustion process, including the use of gas in cooking and internal combustion engines.

The study of the relation between mortality and air pollution was stimulated by the massive number of deaths attributed to an acute episode of smog in London in December 1952. There followed studies of the acute effects of daily changes of pollution in London and in other cities from which the WHO Expert Group. And Task Group concluded that increases in deaths were evident when 24- hour average concentrations of smoke exceeded 500 µg/m³ together with sulfur dioxide above the same value. More recent analyses of past data from London have suggested that variation in daily mortality may be related to variations in daily levels of both pollutants at rather lower levels but problems with confounding factors and disagreement as to which mathematical model is most suitable for describing the data prevent definitive statements about the precise levels at which smoke and sulfur dioxide are associated with acute increases of mortality.

The most often quoted analysis of the long-term effects of air pollution on mortality is that by lave and Seskin . The results of this study were used by the Organization for Economic co-operation and Development (OECD) to estimate the costs of ill health due to sulfur oxides and in particular, sulfates. Despite the (unacknowledged) disagreement of the expert epidemiologists with the approach taken, estimates were made of the number of deaths to be expected for each µg/m³ increase of sulfate in the air and from this was extrapolated the cost of morbidity due to sulfate. The problems with the economical analysis are dealt with later, but here a comment should be made on the limitations of the basic data and the statistical analysis.

The relation was examined between morality from all causes and certain specific causes in selected standard metropolitan statistical areas (SMSAs) in the United States and dir pollutants measured in those areas. Many SMSAs were omitted from the analysis for lack of suitable data- thereby introducing bias of unknown degree into the findings. In some of the SMSAs, the geographical area for which data from only one air pollution monitoring station were available was many hundreds of square miles, thereby leaving uncertain the quantitative value of the dose experienced by the exposed population. The quality of the aerometric data was mot considered, particularly that of the sulfate measurements, which were known to be of questionable validity due to air sampling difficulties. According to the American draft criteria document:

" Clearly, then, no useful information on quantitative relationships between specific concentrations of particulate matter or sulfur oxides and mortality can be derived from these published analyses, nor can any clearly consistent qualitative conclusions regarding particulate matter or Sox air pollution- mortality relationships be drawn based on analogous recent studies.

Recent evidence from the United Kingdom also suggests that current levels of air pollution are unlikely to have detectable long-term effects on morality. A wide range of causes of death in county and London boroughs in 1969 to 1973 was examined in relation to smoke and sulfur dioxide measured in the boroughs. Age- and sex- specific death rates were used and a range of confounding variables wire taken into account including socio-economic factors, latitude, temperature, rainfall, water hardness and a smoking index. Appropriate transformation of the mortality data was made to overcome the problems on non-normality mentioned above. Allowance was also made for the different population sizes of the boroughs. No smoke coefficients was significant (many were negative); sulfur dioxide coefficients were significantly related to total mortality (though not to respiratory disease, as might have been expected ) only on removal from the data set of the London boroughs, where the highest levels of sulfur dioxide were to be found. Comparison with similar analyses done for the period 1948 to 1954 and 18 to 1964 indicated a decline over the 20- year period from strong association between pollution and mortality to none.

Only two studies of the long-term effects of pollution on human morbidity should be mentioned as the many other studies are limited by methodological problems in their relevance to estimating the health costs of pollution. A recent review covers the ground well.

The series of studies by Ferris and co-workers on a sample of the population in Berlin, New Hampshire (United States), shoed that the prevalence of respiratory symptoms declined between 961 and 1966/67 when total suspended particulates (TSP) declined as shown in table 20. There was no change in the prevalence of respiratory symptoms between the years 1966-1967 and 1973. While there were chances in the concentration of sulfur dioxide there were few measurements of this component. The sulfation index as determined from lead dioxide candle measurements was the principal measure of sulfur compounds used in this study; however, they cannot be considered as providing an adequate guide to sulfur dioxide concentrations. Although the data seemed to indicate a relation between morbidity and total suspended particulates (TSP), no relation was found with sulfur oxides. This study was carried out with great, care and attention to epidemiological detail. The major criticism has been the limited quality of the aerometric data over the 12 year period of the study.
 
 

Effects observed	Annual average pollutant levels at which effects noted (µg/m3) TSP SO2
Increased frequency of respiratory symptom; decreased lung function in 5-year olds	360a/	225
Increased frequency of respiratory symptoms	200a/	100
More chronic bronchitis, asthmatic disease In smokers; reduced FEV%	270a/	125
Increased history and symptoms of respiratory Disease	285a/	125
Higher rate of respiratory symptoms; decreased lung function	180	55
Increased frequency of acute lower respiratory disease	135	<25

a/ Converted from smoke to total suspended particulates (TSP) values.

After Ware et al. ( see text for comment).
 

Several reviews of the literature on the effects of oxides of nitrogen on living organisms have appeared . Much of the reported work is about effects on animals. It is now clear, at least in the species which have been investigated, that nitrogen oxides, and more particularly nitrogen dioxide, can cause pathological changes in the lungs such as severe emphysema-like disease in rats and rabbits exposed to high levels over periods of three to six months and, at lower levels, increased susceptibility to respiratory infection in mice.

Some of the experiments were carried out at levels of nitrogen dioxide which are reached, though for much shorter periods, during cooking with gas in unventilated kitchens.

In a study of nitrous fume poisoning in the United Kingdom one man died after exposure to high , but unknown, concentrations of nitrogen dioxide. He appeared to recover from the acute effect but died of acute viral pneumonia 43 days after exposure, which suggested that the exposure to nitrogen dioxide might have increased his susceptibility to infection. These and other high exposure incidents indicate that there are acute effects of nitrous gases on health which may in some cases lead to death either because of increased susceptibility to infection or from pulmonary oedema.

Three studies of respiratory symptoms, two of which included lung function, have been carried out in Chattanooga , Tennessee (United States). The emissions of a trinitrotoluene factory led to high levels of ambient nitrogen dioxide in the nearby community. This community was chosen for study along with two control communities where nitrogen dioxide levels were much lower. The annual average nitrogen dioxide level for 1968/69 were estimated as 90,65 and 45 ppb, respectively, two of them above the current American standard of 50 ppb annual mean.

Between 1968 and 1969 the parents of children in second grade were asked to keep diaries of the respiratory illnesses experienced by themselves and all their children living at home. The lung function of the schoolchildren was also tested on four occasions between November 1968 and March 1969. Analysis of the lung function data [30] indicated that it was not consistently lower in the polluted area over the four examinations.

The most extensive studies directed specifically at the effects of nitrogen dioxide on health have been carried out in the United Kingdom. The first study in a national sample of primary school children showed that those living in electric-cooking homes . This was confirmed four years later in another national sample of primary school children. The second study concentrated on primary school children aged 7 to 8 years in an area two kilometers square of a city in the north of England (Middlesborough, United Kingdom). Measurements of lung function and respiratory health were made on the children and nitrogen dioxide was measured using passive samplers in the children’s bedrooms and in the kitchens. No association was found between lung function and nitrogen dioxide levels, nor between respiratory illness and kitchen nitrogen dioxide levels. But a weak non-significant relation was found with respiratory illness with increasing levels of nitrogen dioxide in the bed room above 20 ppb. A third study (in press) established that this effect was not due to an association between nitrogen dioxide and either bedroom temperature or humidity. This study again suggested a very weak association between bedroom and living room nitrogen dioxide levels and respiratory illness in the children.
 
 

2.2.13 Effects on visibility

The close correlation between sulfates and nitrates in the atmosphere and reduced visibilities has been verified by laboratory measurements. Tang et al. calculated extinction coefficients for mixed ammonium nitrate/ ammonium sulfate aerosols of two compositions under varying humidity conditions. Log-normal particle size distributions with mass median diameters characteristic of the Los Angles aerosol gave extinction coefficient of an externally mixed sulfate/ nitrate aerosol (mixtures of single salt aerosols as opposed to solution droplets of identical composition) that compared well with published statistical correlations derived from Los Angeles visibility data. It also could be shown that sulfates indeed contributed overwhelimingly to visibility reductions in agreement with the findings of white and Roberts.

With the evidence at hand that sulfates in the atmosphere are a dominating visibility-reducing agent and also are subject to long-range transport , it is not surprising that regional visibility reductions are observed worldwide. Waggoner reported simultaneous measurements in Scandinavia of light scattering coefficients and sulfate mass concentrations. A high correlation and agreement with theoretical predictions of the sulfate to light scattering ratio suggested that sulfate was often a dominant substance controlling low visibility and high turbidity. These findings were corroborated by those of Rodhe et al . Who , in addition, provided evidence of the location of sources of the visibility- reducing sulfates. Comparing measurements of sulfates and soot at urban and non-urban locations in southern Sweden with anthropogenic emission sources, it was found that sources 1,000 km away in the south-southwest direction were mainly responsible for the sulfate that was found in southern Sweden.

Barnes and Lee related the long-distance transport of air pollutants and summer visibilities in London(United Kingdom) to sulfate concentrations and wind direction. The results showed the existence of a non-linear, approximately inverse relationship between visibilities and aerosol sulfate concentrations. The worst mean visibility (6.4 km) and the highest daily mean sulfate concentration (16.0 µg m^-3) both occurred in airflows between east and south. The most likely source of the sulfate on these occasions was emissions in continental Europe.

Long-range transport of pollutants plays a role in the relation that has been found between the position of high and low pressure cells and visibility. Vukovich studied ozone, sulfate, total suspended particle concentration and distributions in moving high- pressure systems in the eastern United States.

Typically, as a high pressure system moved into a region, the visibility on the backside relative to the motion of the system decreased significantly. The visibility decrease was accompanied by an increase in total suspended particulate and sulfate concentrations.

Measured and observed visibilities vary between a few and several hundred kilometers, in response to prevailing local/regional climatologies, and to the emission into the atmosphere of natural and /or man-made aerosols. Occasionally, visibilities corresponding to a pure , molecular atmosphere are observed. Of the man-made pollutants, sulfates have been unambiguously kinked to visibility degradations. Given the widespread occurrence of visibility-reduction due to sulfate aerosols, international pollution control strategies aimed at sulfate abatement must be considered by Governments of industrialized nations if further deteriorations of visibilities are to be avoided or if improvements of existing visibilities are to be attempted.

For the sake of research about environmental results of acid deposits , the air quality standards and damage threshold requires budget and monitoring , laboratory, educational, computerized equipments.

With regard to the alternatives executive consequences as it has been demonstrated in flowchart, alternatives launched and its consequences on air quality and threshold pollution damage are surveyed.