#### 3.1. DRF Development

Corrosion of metals in continental regions depends considerably on the content of sulfur dioxide in the air. Therefore, development of a DRF primarily requires that this dependence, i.e., the mathematical relationship

K =

f(SO

_{2}), be found. The dependences reported in graphical form in [

20,

27] differ from each other. The relationship is non-linear, therefore the decision should be made on which background SO

_{2} concentration should be selected, since the calculated

K_{1} values would be smaller than the experimental ones at [SO

_{2}] <1 if non-linear functions are used. [SO

_{2}] values <1 can only be used in linear functions. The background values in

Table 2,

Table 3 and

Table 4 are presented as “Ins.” (Insignificant), ≤1, 3, 5 μg/m

^{3}, which indicates that there is no common technique in the determination of background concentrations. For SO

_{2} concentrations of “Ins.” or ≤1 μg/m

^{3}, we used the value of 1 μg/m

^{3}, whereas the remaining SO

_{2} concentrations were taken from the tables.

In finding the K = f(SO_{2}) relationship, we used the actual test results of all first-year exposures under each program rather than the mean values, because non-linear functions are also used.

The

K =

f(SO

_{2}) relationships obtained for each program are shown in

Figure 1 for steel and in

Figure 2 for zinc. In a first approximation, this relationship can be described by the following function for experimental

K_{1} values obtained in a broad range of meteorological atmosphere parameters:

where

K_{1}° are the average corrosion losses over the first year (g/m

^{2}) in a clean atmosphere for the entire range of

T and

RH values; and

α is the exponent that depends on the metal.

The

K_{1}° values corresponding to the mean values of the parameter range of climatic conditions in clean atmospheres were found to be the same for the experimental data of all programs, namely, 63 and 4 g/m

^{2}, while

α = 0.47 and 0.28 for carbon steel and zinc, respectively. A similar

K_{1}° value for carbon steel was also obtained from the Linear DRF, Equation (6). In fact, at background SO

_{2} concentrations = 1 μg/m

^{3} in PE4 test location (

Table 3) at TOW = 26 h/year (0.002 of the year), the calculated

K_{1}° is to 53 g/m

^{2}, while for CO

_{2} test location at TOW = 8760 h/year (entire year) it is 71 g/m

^{2}; the mean value is 62 g/m

^{2}.

Based on Equation (8), it may be accepted in a first approximation that the effect of [SO_{2}] on corrosion is the same under any climatic conditions and this can be expressed in a DRF by an [SO_{2}]^{α} multiplier, where α = 0.47 or α = 0.28 for steel or zinc, respectively. The K_{1}° values in Equation (8) depend on the climatic conditions and are determined for each test location based on the atmosphere meteorological parameters.

In the development of New DRF, the

K_{1} values were determined using the DRF mathematical formula presented in the Standard DRF and in the Unified DRF, as well as meteorological parameters

T,

RH, and

Prec (

Rain for warm climate locations or

Prec for cold climate locations). The complex effect of

T was taken into account: corrosion losses increase with an increase in

T to a certain limit,

T_{lim}; its further increase slows down the corrosion due to radiation heating of the surface of the material and accelerated evaporation of the adsorbed moisture film [

12,

28]. It has been shown [

29] that

T_{lim} is within the range of 9–11 °C. Similarly to Equations (3)–(6), it is accepted that

T_{lim} equals 10 °C. The need to introduce

Prec is due to the fact that in northern RF regions, the

K_{1} values are low at high

RH, apparently owing not only to low

T values but also to the small amount of precipitation, including solid precipitations. The values of the coefficients reflecting the effect of

T,

RH and

Prec on corrosion were determined by regression analysis.

The New DRFs developed for the prediction of K_{1} (g/m^{2}) for the two temperature ranges have the following forms:

for carbon steel :

and for zinc:

#### 3.2. Predictions of K_{1} Using Various DRFs for Carbon Steel

Predictions of

K_{1} were performed for all continental test locations with chloride deposition rates ≤2 mg/(m

^{2}·day). The results of

K_{1} prediction (

K_{1}^{pr}) from Equations (3)–(7), (9), and (10) are presented separately for each test program. To build the plots, the test locations were arranged by increasing experimental

K_{1} values (

K_{1}^{exp}). Their sequence numbers are given in

Table 2,

Table 3 and

Table 4. The increase in

K_{1} is caused by an increase in atmosphere corrosivity due to meteorological parameters and SO

_{2} concentration. All the plots are drawn on the same scale. All plots show the lines of prediction errors

δ = ±30% (the 1.3

K_{1}^{exp}–0.7

K_{1}^{exp} range). This provides a visual idea of the comparability of

K_{1}^{pr} with

K_{1}^{exp} for each DRF. The scope of this paper does not include an estimation of the discrepancy between the

K_{1}^{pr} values obtained using various DRFs with the

K_{1}^{exp} values obtained for each test location under the UN/ECE and RF programs. The scatter of points is inevitable. It results from the imperfection of each DRF and the inaccuracy of experimental data on meteorological parameters, SO

_{2} content, and

K_{1}^{exp} values. Let us just note the general regularities of the results on

K_{1}^{pr} for each DRF.

The results on

K_{1}^{pr} for carbon steel for the UN/ECE program, MICAT project, and RF program are presented in

Figure 3,

Figure 4 and

Figure 5, respectively. It should be noted that according to the Unified DRF (Equation (5)), the

K_{1}^{pr} of carbon steel in RF territory [

30] had low values. It was also found that the

K_{1}^{pr} values are very low for the programs mentioned above. Apparently, the

K_{1}^{pr} values (Equation (5)) were calculated in μm rather than in g/m

^{2}, as the authors assumed. To convert

K_{1}^{pr} in μm to

K_{1}^{pr} in g/m

^{2}, the 3.54 coefficient in Equation (6) was increased 7.8-fold.

In the UN/ECE program, the

K_{1}^{pr} values match

K_{1}^{exp} to various degrees; some

K_{1}^{pr} values exceed the error

δ (

Figure 3). Let us describe in general the locations in which

K_{1}^{pr} values exceed

δ. For the New DRFs (

Figure 3a) there are a number of locations with overestimated

K_{1}^{pr} and with underestimated

K_{1}^{pr} values at different atmosphere corrosivities. For the Standard DRF (

Figure 3b) and Linear DRF (

Figure 3d), locations with underestimated

K_{1}^{pr} values prevail, also at different

K_{1}^{exp}. For the Unified DRF (

Figure 3c),

K_{1}^{pr} are overestimated for locations with small

K_{1}^{exp} and underestimated for locations with high

K_{1}^{exp}. The possible reasons for such regular differences for

K_{1}^{pr} from

K_{1}^{exp} will be given based on an analysis of the coefficients in the DRFs.

For the MICAT project,

K_{1}^{pr} considerably exceeds

δ for all DRFs in many locations (

Figure 4). Overestimated and considerably overestimated

K_{1}^{pr} values are mainly observed in locations with small

K_{1}^{exp}, while underestimated

K_{1}^{pr} values are mainly observed for locations with high

K_{1}^{exp}. Furthermore, for the Linear DRF (

Figure 4d), particularly overestimated values are observed in location B6 (No. 31, No. 53, and No. 54) at all exposures. This test location should be noted. The corrosivity parameters under this program reported in [

20] are different for some test locations (

Table 3). In fact, for B6, the [SO

_{2}] value for all exposures is reported to be 28 μg/m

^{3} instead of 67.2; 66.8 and 48.8 μg/m

^{3}.

Figure 4e presents

K_{1}^{pr} for the Linear DRF with consideration for the parameter values reported in [

20]. Naturally,

K_{1}^{pr} for B6 decreased considerably in comparison with the values in

Figure 4d but remained rather overestimated with respect to

K_{1}^{exp}.

If all DRFs give underestimated

K_{1}^{pr} values for the same locations, this may result from an inaccuracy of experimental data, i.e., corrosivity parameters and/or

K_{1}^{exp} values. We did not perform any preliminary screening of the test locations. Therefore, it is reasonable to estimate the reliability of

K_{1}^{exp} only in certain locations by comparing them with other locations. Starting from No. 26,

K_{1}^{pr} values are mostly either smaller or considerably smaller than

K_{1}^{exp}. The locations with underestimated

K_{1}^{pr} that are common to all DRFs include: A4 (No. 5, No. 6), B1 (No. 28), B10 (No. 26), B11 (No. 41), E1 (No. 47, No. 48, No. 51), E4 (No. 43, 49, 50), EC1 (No. 45, No. 52, No. 56), CO3 (No. 40, 57), PE4 (No. 32, No. 39), M3 (No. 58, No. 60, No. 62). To perform the analysis,

Table 6 was composed. It contains the test locations that, according to our estimates, have either questionable or reliable

K_{1}^{exp} values. It clearly demonstrates the unreliability of

K_{1}^{exp} in some test locations. For example, in the test locations PE4 and A4, with

RH = 33%–51% and

TOW = 0.003–0.114 of the year at background [SO

_{2}],

K_{1}^{exp} are 4.5–16.5 μm (35.1–117 g/m

^{2}), while under more corrosive conditions in E8 and M2 with

RH = 52%–56% and

TOW = 0.100–0.200 of the year and [SO

_{2}] = 6.7–9.9 μg/m

^{3},

K_{1}^{exp} values are also 3.3–15.2 μm (25.7–118.6 g/m

^{2}). The impossibility of high

K_{1} values in PE4 and A4 is also confirmed by the 3D graph of the dependence of

K on SO

_{2} and

TOW in [

20]. Alternatively, for example, in B1, CO3 and B11 with

RH = 75%–77% and

TOW = 0.172–0.484 of the year and [SO

_{2}] = 1–1.7 μg/m

^{3},

K_{1}^{exp} = 13.1–26.2 μm (102.2–204.4 g/m

^{2}), whereas in A2 and A3 with

RH = 72%–76% and

TOW = 0.482–0.665 of the year and [SO

_{2}] = 1–10 μg/m

^{3},

K_{1}^{exp} is as small as 5.6–16.1 μm (43.7–125.6 g/m

^{2}). The

K_{1} values reported for locations with uncertain data are 2–4 times higher than the

K_{1} values in trusted locations. The reason for potentially overestimated

K_{1}^{exp} values being obtained is unknown. It may be due to non-standard sample treatment or to corrosion-related erosion. It can also be assumed that the researchers (performers) reported

K_{1} in g/m

^{2} rather than in μm. If this assumption is correct, then

K_{1}^{pr} values would better match

K_{1}^{exp} (

Figure 4). Unfortunately, we cannot compare the questionable

K_{1}^{exp} values with the

K_{1}^{exp} values rejected in the study where an artificial neural network was used [

20]. We believe that, of the

K_{1}^{exp} values listed, only the data for the test locations up to No. 26 in

Figure 4 can be deemed reliable.

For the RF program, the

K_{1}^{pr} values determined by the New DRF and the Standard DRF are pretty comparable with

K_{1}^{exp}, but they are considerably higher for the Unified DRF (

Figure 5).

The presented figures indicate that all DRFs which have the same parameters but different coefficients predict

K_{1} for same test locations with different degrees of reliability. That is, combinations of various coefficients in DRFs make it possible to obtain

K_{1}^{pr} results presented in

Figure 3,

Figure 4 and

Figure 5. In view of this, the analysis of DRFs in order to explain the principal differences of

K_{1}^{pr} from

K_{1}^{exp} for each DRF appears interesting.

#### 3.3. Analysis of DRFs for Carbon Steel

The DRFs were analyzed by comparison of the coefficients in Equations (3), (5) and (9). Nonlinear DRFs can be represented in the form:

or

where

A × e

^{k}^{1·RH} × e

^{k}^{2·(T−10)} × e

^{k}^{3·Prec} =

K_{10}.

The values of the coefficients used in Equations (3), (5) and (9) are presented in

Table 7.

To compare the

α values,

K_{1}° = 63 g/m

^{2} at [SO

_{2}] = 1 μg/m

^{3} was used in Equation (8) for all DRFs. The [SO

_{2}]

^{α} plots for all the DRFs for all programs are presented in

Figure 1. For the New DRF, the line

K =

f(SO

_{2}) was drawn approximately through the mean experimental points from all the test programs. Therefore, one should expect a uniform distribution of error

δ, e.g., in

Figure 3a. For the Standard DRF,

α = 0.52 is somewhat overestimated, which may result in more overestimated

K_{1} values at high [SO

_{2}]. However, in

Figure 3b for CS1 (No. 76), CS3 (No. 73, 74, 77) and GER10 (No. 76),

K_{1}^{pr} overestimation is not observed, apparently due to effects from other coefficients in DRF. For Unified DRF

α = 0.13, which corresponds to a small range of changes in

K_{1} as a function of SO

_{2}. Therefore, in

Figure 3c and

Figure 4c, the

K_{1}^{pr} present a nearly horizontal band that is raised to the middle of the

K_{1}^{exp} range due to a higher value of

A = 3.54 μm (27.6 g/m

^{2}),

Table 7. As a result, the Unified DRF cannot give low

K_{1}^{pr} values for rural atmospheres,

Figure 3c and

Figure 5c, or high

K_{1}^{pr} values for industrial atmospheres,

Figure 3c.

For the Linear DRF we present

K_{1}^{pr}—[SO

_{2}] plots for

TOW (fraction of a year) within the observed values: 0.043–0.876 for ISO CORRAG program; 0.5–1 based on the data in [

19]; 0.17–0.62 from UN/ECE program; 0.003–1 from the MICAT project, and 0.002–0.8 based on the data [

20] for the MICAT project,

Figure 1. One can see that reliable

K_{1}^{pr} are possible in a limited range of

TOW and [SO

_{2}]. The

K_{1}^{pr} values are strongly overestimated at high values of these parameters (

Figure 4c,d). That is, the Linear model has a limited applicability at combinations of

TOW and [SO

_{2}] that occur under natural conditions. Furthermore, according to the Linear DRF, the range of

K_{1}^{pr} in clean atmosphere is 53–71 g/m

^{2}, therefore the

K_{1}^{pr} values in clean atmosphere lower than 53 g/m

^{2} (

Figure 3d and

Figure 4d,e) or above 71 g/m

^{2} cannot be obtained. Higher

K_{1}^{pr} values can only be obtained due to [SO

_{2}] contribution. The underestimated

K_{1}^{pr} values in comparison with

K_{1}^{exp} for the majority of test locations (

Figure 3d) are apparently caused by the fact that the effects of other parameters, e.g.,

T, on corrosion are not taken into account.

Figure 6 compares

K =

f(SO

_{2}) for all the models with the graphical representation of the dependence reported in [

20] (for [SO

_{2}], mg/(m

^{2}·d) values were converted to μg/m

^{3}). The dependence in [

20] is presented for a constant temperature, whereas the dependences given by DRFs are given for average values in the entire range of meteorological parameters in the test locations. Nevertheless, the comparison is of interest. Below 70 and 80 μg/m

^{3}, according to [

20],

K has lower values than those determined by the New DRF and Standard DRF, respectively, while above these values,

K has higher values. According to the Unified DRF,

K has extremely low values at all [SO

_{2}] values, whereas according to the Linear DRF (TOW from 0.03 to 1), the values at

TOW = 1 are extremely high even at small [SO

_{2}].

To perform a comparative estimate of

k_{1} and

k_{2}, let us use the value

T_{lim} = 10 °C accepted in the DRF, i.e., where the temperature dependence changes. Furthermore, it is necessary to know the

K_{1} value in clean atmosphere at

T_{lim} and at the

RH that is most common at this temperature. These data are unknown at the moment. Therefore, we’ll assume that at

T_{lim} = 10 °C and

RH = 75%,

K = 63 g/m

^{2}. The dependences of

K on

T and

RH under these conditions and with consideration for the corresponding

k_{1} and

k_{2} for each DRF are presented in

Figure 7.

The nearly coinciding

k_{1} values (0.020 for the Unified DRF and Standard DRF, and 0.024 for the New DRF,

Table 8) result in an insignificant difference in the

RH effect on

K (

Figure 7a).

The temperature coefficient

k_{2} has a considerable effect on

K. For the Unified

DRF, the

k_{2} values of 0.059 (−0.036) for

T ≤ 10 °C (

T > 10 °C) create the lowest decrease in

K with a

T decrease (increase) in comparison with the other DRFs (

Figure 7b). A consequence of such

k_{2} values can be demonstrated by examples. Due to the temperature effect alone,

K ~ 15 g/m

^{2} at

T = −12 °C (

Figure 7b) and

K~45 g/m

^{2} at

T = 20 °C. The effects of other parameters and account for the

A value would result in even more strongly overestimated

K^{pr} values. For comparison: in Bilibino at

T = −12.2 °C and

RH = 80%,

K_{1}^{exp} = 5.4 g/m

^{2} (

Table 4) and

K^{pr} = 42 g/m

^{2} (

Figure 5). In A3 test location, at

T = 20.6 °C and

RH = 76%,

K_{1}^{exp} = 44.5 g/m

^{2} (

Table 4), while due to

A and other parameters,

K_{1}^{pr} = 86.2 g/m

^{2},

Figure 4c.

In the Standard DRF, the

k_{2} values are higher than in the Unified DRF: 0.150 and −0.054 for

T ≤ 10 °C and

T > 10 °C, respectively, so a greater

K decrease is observed, especially at

T ≤ 10 °C,

Figure 7b. At low

T, the

K values are small, e.g.,

K ~ 2 g/m

^{2} at

T = −12 °C. In

K_{1}^{pr} calculations, the small

K are made higher due to

A, and they are higher in polluted atmospheres due to higher

α = 0.52. As a result,

K^{pr} are quite comparable with

K^{exp},

Figure 3b. However, let us note that

K^{pr} is considerably lower than

K^{exp} in many places. Perhaps, this is due to an abrupt decrease in

K in the range

T ≤ 10 °C. This temperature range is mostly met in test locations under the UN/ECE program.

In the New DRF,

k_{2} has an intermediate value at

T ≤ 10 °C and the lowest value at

T > 10 °C, whereas

A has the lowest value. It is more difficult to estimate the

k_{2} value with similar

k_{2} values in the other DRFs, since the New DRF uses one more member, i.e., e

^{k}^{3·Prec}. The dependence of

K on

Prec is presented in

Figure 7c. The following arbitrary values were used to demonstrate the possible effect of

Prec on

K:

K = 7.8 g/m

^{2} at

Prec = 632 mm/year. For example, in location PE5 (UN/ECE program) with

Prec = 632 mm/year,

K = 7.8 g/m

^{2} at

T = 12.2 °C and

RH = 67%. The maximum

Prec was taken as 2500 mm/year, e.g., it is 2144 mm/year in NOR23 (UN/ECE program) and 2395 mm/year in B8 (MICAT project). It follows from the figure that, other conditions being equal,

K can increase from 5.4 to 22.6 g/m

^{2} just due to an increase in

Prec from 0 to 2500 mm/year at

k_{3} = 0.00056 (

Table 7).

Thus, it has been shown that the coefficients for each parameter used in the DRFs vary in rather a wide range. The most reliable K_{1}^{pr} can be reached if, in order to find the most suitable coefficients, the DRFs are based on the K = f(SO_{2}) relationship obtained.

#### 3.4. Predictions of K_{1} Using Various DRFs for Zinc

The results on

K_{1}^{pr} for zinc for the UN/ECE program, MICAT project, and RF program are presented in

Figure 8,

Figure 9 and

Figure 10, respectively. In the UN/ECE program, the differences between the

K_{1}^{pr} and

K_{1}^{exp} values for zinc are more considerable than those for carbon steel. This may be due not only to the imperfection of the DRFs and the inaccuracy of the parameters and

K_{1}^{exp}, but also to factors unaccounted for in DRFs that affect zinc. For all the DRFs, the

K_{1}^{pr} values match

K_{1}^{exp} to various extent; some of the latter exceed the error

δ (±30%). Let us estimate the discrepancy between

K_{1}^{pr} and

K_{1}^{exp} for those

K_{1}^{pr} that exceed

δ. For the New DRF (

Figure 8a) and the Standard DRF (

Figure 8b), overestimated

K_{1}^{pr} values are observed for low and medium

K_{1}^{exp}, while underestimated ones are observed for medium and high

K_{1}^{exp}. In general, the deviations of

K_{1}^{pr} from

K_{1}^{exp} are symmetrical for these DRFs, but the scatter of

K_{1}^{pr} is greater for the Standard DRF. For Unified DRF (

Figure 8c),

K_{1}^{pr} are mostly overestimated, considering that the ∆

K^{[H+]} = 0.029

Rain[H

^{+}] component was not taken into account for some test locations due to the lack of data on [H

^{+}]. The ∆

K^{[H+]} value can be significant, e.g., 2.35 g/m

^{2} in US39 or 5.13 g/m

^{2} in CS2.

With regard to the MICAT project, the New and Unified DRFs (

Figure 9a,c) give overestimated

K_{1}^{pr} at low

K_{1}^{exp}, but the Standard DRF gives

K_{1}^{pr} values comparable to

K_{1}^{exp} (

Figure 9b). Starting from test locations No. 33–No. 36, the

K_{1}^{pr} values for all the DRFs are underestimated or significantly underestimated. It is evident from

Figure 2b that rather many test locations with small [SO

_{2}] have extremely high

K_{1}^{exp}. This fact confirms the uncertainty of experimental data from these locations, as shown for carbon steel as well. The following test locations can be attributed to this category: A3 (No. 43, No. 44, No. 53), B10 (No. 50), B11 (No. 49), B12 (No. 57), CO2 (No. 55, No. 58, No. 60), CO3 (No. 54, No. 61), PE6 (No. 36, No. 38), and M3 (No. 35, No. 59). There is little sense in making

K_{1} predictions for these locations.

For the RF program, the

K_{1}^{pr} values calculated by the New and Unified DRFs are more comparable to

K_{1}^{exp} than those determined using the Standard DRF (

Figure 10).

#### 3.5. Analysis of DRFs for Zinc

As for steel, DRFs were analyzed by comparison of their coefficients. The nonlinear DRFs for zinc can be represented in the form:

or

The values of the coefficients used in Equations (4), (6) and (10) are presented in

Table 8.

To compare the

α values,

K_{1} = 4 g/m

^{2} at [SO

_{2}] = 1 μg/m

^{3} was used for all DRFs. Let us note that the value

K_{1} = 4 g/m

^{2} was obtained during the estimation of

K =

f(SO

_{2}) for the development of the New DRF. The plots for all the programs are presented in

Figure 2. For the New DRF, the line at

α = 0.28 mostly passes through the average experimental points. For the Standard DRF,

α = 0.44 is overestimated considerably, which may result in overestimated

K_{1}^{pr}, especially at high [SO

_{2}]. For the Unified DRF at

α = 0.22, the line passes, on average, slightly below the experimental points. The low

α value, as for carbon steel, does not give a wide range of

K values as a function of [SO

_{2}], which may result in underestimated

K_{1}^{pr}, especially at high [SO

_{2}].

Let us assume for a comparative estimate of

k_{1} and

k_{2} that

K = 4 g/m

^{2} in a clean atmosphere at

T_{lim} = 10 °C and

RH = 75%.

Figure 11 demonstrates the plots of

K versus these parameters under these starting conditions. The Standard DRF (

k_{1} = 0.46) shows an abrupt variation in

K vs.

RH. According to this relationship, at the same temperature, the

K value should be 0.5 g/m

^{2} at

RH = 30% and 12.6 g/m

^{2} at

RH = 100%. According to the New DRF and Unified DRF with

k_{1} = 0.22 and 0.18, respectively, the effect of

RH is weaker, therefore

K = 1.5 and 1.8 g/m

^{2} at

RH = 30%, respectively, and

K = 6.9 and 6.4 g/m

^{2} at

RH = 100%, respectively.

The effect of temperature on

K is shown in

Figure 11b. In the New DRF,

k_{2} = 0.045 at

T ≤ 10 °C has an intermediate value; at

T > 10 °C,

k_{2} = −0.085 has the largest absolute value, which corresponds to an abrupt decrease in

K with an increase in temperature. In the Unified DRF,

k_{2} = −0.021 at

T > 10 °C, i.e., an increase in temperature results in a slight decrease in

K. As for the effect of

A, this also contributes to higher

K_{1}^{pr} values despite the small

α value.

In the Standard DRF, the value

A = 0.0929 (g/m

^{2}), which is ~8 times smaller than in the New DRF, and a small

k_{2} = −0.71 at

T > 10 °C were taken to compensate the

K_{1}^{pr} overestimation due to the combination of high values,

α = 0.44 and

k_{1} = 0.46. In the Unified DRF, the high

A value that is ~2 times higher than in the New DRF is not compensated by the combination of the low values,

α = 0.22 and

k_{2} = −0.021 at

T > 10 °C. Therefore, the

K_{1}^{pr} values are mostly overestimated,

Figure 8c and

Figure 9c for trusted test locations. However, small

K_{1}^{pr} values were attained for low

T at

k_{2} = 0.62,

Figure 10c.

The effect of

Prec on

K at

k_{3} = 0.0001, which is taken into account only in the New DRF, given under the assumption that

K = 0.65 in a clean atmosphere at

Prec (

Rain) = 250 mm/year,

T = 15 °C and

RH = 60% (e.g., location E5 in the MICAT project), is shown in

Figure 11c. Upon an increase in

Prec (

Rain) from 250 to 2500 mm/year,

K can increase from 0.65 to 0.81 g/m

^{2}.

As for carbon steel, the above analysis of coefficients in the DRFs for zinc confirms that the coefficients can be varied to obtain reliable K_{1}^{pr} values. The New DRF based on K = f(SO_{2}) gives the most reliable K_{1}^{pr} values for zinc.