10/12/99

Preliminary Air Quality Related Screening Values for

 the James River Face Wilderness, a Class I Area in Virginia.

October 1999

Work is currently underway to assist applicants of Prevention of Significant Deterioration 

(PSD) permits determine if a new source of pollution will have an adverse impact on any 

air quality related value in James River Face Wilderness located near Natural Bridge, VA. 

Table 1 lists the red line and green line screening values for several types of pollutants

which have the potential to adversely impact the air quality related values. The red line

values indicates a total pollution level (new source plus ambient) where at least one air

quality related value has a high likelihood of having an adverse impact; whereas the green 

line value indicates a total pollution level where there is a low likelihood of an adverse

impact to the air quality related values. Values that are between the red line value and

green line value are classified as the yellow zone. The yellow zone is an area where there 

is uncertainty that one or more air quality related values will have an adverse impact. 

The user of the information needs to understand that the values presented are used by

people at the George Washington and Jefferson National Forests to assess the risk of a

new source of air pollution. The exceeding of a red line value by current monitored or

estimated values does not mean the Federal Land Manger will issue an adverse impact

determination to the air regulatory authority. Neither does a value between the red and

green line values (i.e. the yellow zone) mean that an adverse impact determination will not 

be recommended to the air regulatory agency. Other data are often used, which are not

presented here, before issuing an adverse impact determination. For example, the

applicant may want to collect acidic deposition information near the Class I area to

estimate the total deposition of sulfate and nitrates for a particular year. Furthermore, an 

applicant could recommend ways to mitigate, or offset the new emissions of one or more 

air pollutants. 

The sections following Table 1 briefly describe each of the pollutants which have the

potential to have an adverse impact on the air quality related values. Another document 

will be released at a future date which will provide greater detail on how the pollutants

impact the resources and how the screening level values were selected.
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Table 1. Red line and green line screening values for the Class I area, and current 

monitored or estimated values. 

 Current Values

Pollutant Red Line Green Line Averaging James River

Name Value Value Unit of Measure Period Face

Ozone > 23.7 <5.9 W126 (ppm-hrs.) April - October 41.9

Ozone >50 <6 # hrs. >= 0.10 ppm April - October 7

Sulfate >=60 <15 kg/ha/yr Annual 55

Nitrate >=44 <13 kg/ha/yr Annual 32

Sulfate + Nitrate <25.0 >=25.0 ANC, ueq/L Spring 3

Sulfate + Nitrate <0 >0 ANC, ueq/L Episodic ND

Sulfate + Nitrate <=6.0 >6.0 pH units Spring 5.7

Sulfate + Nitrate <=5.5 >5.5 pH units Episodic ND

Paticulates and NO2 >=2.0 <2.0 ΔE Hourly NA

Paticulates and NO2 >=0.05 <0.05 contrast Hourly NA

PM 2.5 >= 5% < 5% b ext Daily *

NA = not applicable

ND = no data available at this time

* Current visibility values are expressed as bext in inverse megameters (Mm-1). See Table 2 for values.

Ozone: A high seasonal exposure and frequent occurrence of peak hourly ozone

concentrations (>= 0.10 ppm) are needed to reduce the growth of tree species found in the 

southern Appalachians (Lefohn et al. 1997, and SAMAB 1996). Therefore, a dual

parameter screening level value is used to determine if ground level ozone will cause an

adverse impact to the vegetation resources at the Class I area. An adverse impact is likely 

to occur when the W126, a measure of the seasonal exposure (Lefohn and Runeckles

1987), is greater than 23.7 ppm-hours; and there are more than 50 hours during the

growing season (April through October) when the average hourly ozone concentration is 

0.10 ppm or greater. Currently, there is no EPA approved method to estimate ozone

increases from a single source. The preferred method for addressing ground-level ozone 

is to reduce emissions on a regional scale. The air regulatory agencies and applicants will 

be informed early in the application process if ozone exposures are believed to be causing 

an adverse impact to terrestrial resources. Table 1 shows that the W126 value exceeds the 

red line value. The frequency of peak hourly ozone concentrations are below the red line 

value, but above the green line value. These results do not clearly demonstrate that ozone 

exposures are having an adverse impact on the vegetation. Therefore, other data and/or

published results will be used to determine if an adverse impact is occurring to the

terrestrial resources at the Wilderness.

Sulfate: Deposition of sulfates from the atmosphere occur in wet (rainfall), dry, and

cloudwater forms. Increases in sulfates have the potential to have an adverse impact on

soil chemistry, which could lead to adverse impacts to soil and vegetation air quality

related values. Sulfate deposition at the three Class I areas was estimated using the sulfate 

modeling results reported in the Southern Appalachian Assessment (SAMAB 1996, Lynch 

and others 1996). The numbers reported represent sulfate from only rainfall which 
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underestimates the total sulfate deposition. Studies conducted at the Great Smoky

Mountains National Park have demonstrated that dry sulfate deposition is equivalent to

sulfate from rainfall. Sulfate from cloudwater is approximately twice the rainfall plus dry 

sulfate deposition (Johnson and Lindberg 1992). The total deposition results in Table 1

were obtained by doubling the modeled sulfate results presented in the Southern

Appalachian Assessment (SAMAB 1996). The values presented in Table 1 do not include 

cloudwater.

Current sulfate deposition at James River Face Wilderness is estimated to be 55 kg/ha/yr 

(i.e. in the yellow zone) which is below the red line of 60 kg/ha/yr. Applicants will need to 

follow Section 5.1.3 of the Interagency Workgroup on Air Quality Modeling guidelines

(EPA, 1993) when converting the screening model (Level 1) values for sulfate deposition. 

If the screening model values are predicted to be greater than or equal to 0.03 kg/ha (see 

Appendix A) then the applicant should use the CalMet and CalPuff models for subsequent 

analysis.

Nitrate: Deposition of nitrates from the atmosphere occur in wet (rainfall), dry, and

cloudwater (SAMAB 1996). As with sulfates, an increase in nitrates has the potential to 

adversely impact soils, and vegetation air quality related values (Peterjohn and others

1996). The nitrate values in Table 1 were obtained by doubling the wet nitrate estimates 

found in the Southern Appalachian Assessment data (SAMAB 1996, and Lynch and

others 1996). The Class I area value falls within the yellow zone, which means other

information is needed to determine if an adverse impact is likely to occur. Excessive

amounts of nitrates have been found to be present at the Great Smoky Mountains National 

Park (Nodvin and others 1995). There is a possibility that nitrogen saturation could also 

be occurring at James River Face. Applicants will need to follow Section 5.1.3 of the

Interagency Workgroup on Air Quality Modeling guidelines (EPA, 1993) when converting 

the screening model (Level 1) values for nitrate deposition. If the screening model values 

are predicted to be greater than or equal to 0.03 kg/ha (see Appendix A) then the

applicant should use the CalMet and CalPuff models for subsequent analysis.

Sulfate + Nitrate: The red values for sulfate and nitrate numbers presented in Table 1 are 

given as an indicator where soil and vegetation air quality related values could be

adversely impacted. Acidic deposition can also have an adverse impact on water air

quality related values because the acidified rainwater or soil water moves into the stream. 

Adverse effects can occur to water quality and aquatic organisms (especially some fish and 

aquatic insects) if the acidified soil water is not neutralized. The acid neutralizing capacity 

(ANC) is a water chemistry measurement which reflects the ability of a watershed to offset 

the acid inputs. Aquatic biota are at risk of adverse impacts if the spring stream ANC

values are less than 25.0 ueq/l. Furthermore, aquatic biota are at risk if the ANC values 

are less than 0 ueq/l following a rain storm (i.e. episodic event). Water is an air quality

related value at James River Face Wilderness, and spring time water chemistry samples

have been collected. The lowest ANC recorded over the past five years is 3 ueg/l, which 

is well below the red line value. The CalMet and CalPuff models should be used if the

steady state ANC levels are predicted to decrease equal to or greater than 0.1 ueq/l.
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pH is another important water chemistry measurement used to indicate the status of the

water as an air quality related value. Streams with a pH value of less than or equal to 6.0 

in the spring time could have adverse impacts to the stream biota. Adverse impacts can

also occur if the pH is less than or equal to 5.5 following a rain storm. The lowest spring 

time pH measurement for James River Face Wilderness is 5.7, which is below the red line 

value. The CalMet and CalPuff model should be used if the pH levels are predicted to

decrease less than or equal to 0.01 units.

Particulates and NO2: Some facilities which emit particulates, nitrogen dioxide (NO2), 

and sometimes hydrogen sulfides (H2SO4) can produce a plume that can be seen in or

outside of the Class I area. The EPA has recommended a method to assess impacts from 

coherent plumes from sources less than 50 km from the Class I area. The VISCREEN

(EPA, 1988) and PLUVUE-II (EPA, 1995) models are recommended to conduct plume

blight analysis. These two models calculate the change in color (ΔE) and contrast 

between the plume and the viewing background. Sources should perform the analysis

using the existing emissions plus any additional emissions proposed. The model results are 

significant if the ΔE value is 2.0 or greater, and/or the contrast value is 0.05 or greater. 

PM2.5: New sources emission increases can result in plume blight if they are 50 km or

less from the Class I areas, but all sources have the potential to contribute to regional

haze. The main type of visibility reductions at Class I areas is regional haze (SAA 1996), 

and any PSD analysis needs to focus on what a new source’s contributions will be to

regional haze. Fine particles (2.5 microns or smaller) are primarily responsible for

reducing visibility at the Class I areas. The most important types of fine particles are:

sulfates, organics, nitrates, elemental carbon and soil. In addition, coarse particles

(between 2.5 and 10 microns) contribute somewhat to visibility impairment. The

Environmental Protection Agency (EPA) has published a document with

recommendations for modeling impacts on regional haze (EPA 1993), but the following

steps should be followed instead of the guidance given by the EPA (1993):

1. Use the 24-hour modeling results for NOx and SOx concentrations for 

one year. Assume all NOx forms ammonium nitrate and all SOx forms 

ammonium sulfate. (Multiply the mass concentration of SO4

-2

 by 1.375 

to obtain (NH4)2SO4. Likewise, multiply the mass concentration of

NO3

-

 by 1.29 to obtain NH4NO3.)
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2. Get the Seasonal Clear-day Aerosol Profile data for all the modeling

receptors for James River Face Wilderness from Table 2. The numbers 

in Table 2 are taken from an IMPROVE (Interagency Monitoring of

Protected Visual Environments) monitoring site near James River Face 

Wilderness

Table 2. Seasonal Clear-day Aerosol Profile (background) for James River Face

IMPROVE monitoring Site (8/94-9/96). 

Spring 

(μg/m3)

Summer

(μg/m3)

Autumn

(μg/m3)

Winter

(μg/m3)

Extinction

Efficiency

Ammonium 

Sulfate

3.09 5.36 2.46 2.58 3xf(RH)

Ammonium 

Nitrate

.61 .42 .41 .72 3xf(RH)

Soil .41 .73 .30 .25 1

Organics 1.78 2.84 2.21 2.43 4

Elemental Carbon .52 .49 .50 .53 10

Coarse Mass 5.318 4.12 3.48 3.2 0.6

10thβext (inverse Mm) 61 105 62 63

10th Standard visual range 64 37 63 62

The following months should be used for each of the seasons listed in Table 

2:

Spring: March, April, and May

Summer: June, July, and August

Autumn: September, October, and November

Winter: December, January and February

3. For each day, calculate reconstructed light extinction for background

conditions and the new source, using the data in Table 2 for

background. This calculation is performed assuming an externally

mixed aerosol, so that the total extinction of the aerosols present is

equal to the sum of the extinctions of each of the species. Each

species’ concentration is multiplied by a dry extinction efficiency to

determine the amount of extinction it causes. For hygroscopic species 

(ammonium sulfate and ammonium nitrate), this dry extinction must be 

multiplied by f(RH) to correct for the effects of relative humidity. The 

f(RH) curve is in the EPA (1993) document. For computer algorithms, 

interpolate from values in Table B-1 (EPA, 1993).

Note: It is important to calculate f(RH) for each hour of the day being

modeled. These 24 hourly f(RH) values should then be averaged to give a 

24-hour average f(RH). Do not use the 24-hour average RH to calculate 

the daily f(RH).
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4. Calculate the change in βext for each day. For the purpose of definition:

Δβext = source βext / background βext

The red line value is exceeded when the background βext change will be greater than or

equal to 5 percent for any day during the year (Table 1). Likewise, the atmospheric

modeling significance value is also the same as the red line value and the CalMet and

CalPuff models should be used if the change in βext is predicted to be greater than or equal 

to 5 percent for any day during the year.

The following is for example only:

The modeling results predict the 24-hour average SO4 concentration will

increase by 0.9 μg/m3 on December 10th at one of the receptors at James

River Face Wilderness. All of the SO4 increase will be assumed to form

ammonium sulfate. Therefore, the increase in ammonium sulfate is

predicted to be 1.2375 μg/m3. The f(RH) was calculated for each hour on 

December 10th and the average of the 24 hourly values was 3. Using these 

values the background βext is:

[2.58(3(3))]+[.72(3(3))]+[.25(1)]+[2.43(4)]+[.43(10)]+[3.2(0.6)] 

23.22 + 6.48 + 0.25 + 9.72 + 4.3 + 1.92 = 45.89 Mm-1

Extinction attributable to the new source (with ammomium sulfate impact

of 1.2375 μg/m3) would be:

[1.24(3(3))]+[0(3(3))]+[0(1)]+[0(4)]+[0(10)]+[0(0.6)] 

11.16 + 0 + 0 + 0 + 0 + 0 = 11.16 Mm-1

Therefore, the percent change in βext is:

11.16 / 45.89 = .24 or 24 percent

A βext increase of 24 percent would exceed the red line value of 5 percent. 

If these were the results from a screening model, then the applicant should 

proceed to use the CalMet and CalPuff model to see if the SOx modeled

value would decrease. Another option would be to use a better control

technology, or seek emissions offsets that would reduce the visibility

impact.
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Literature Cited

Environmental Protection Agency (EPA). 1988. Workbook for plume visual impact

screening and analysis. EPA-450/4-88-015.

Environmental Protection Agency (EPA). 1993. Interagency Workgroup on Air Quality 

Modeling (IWAQM), Phase I Report: Interim recommendations for modeling long range 

transport and impacts on visibility. EPA-454/R-930015.

Environmental Protection Agency (EPA) 1995. PLUVUE-II (96170).

Johnson , D.; Lindberg, S., eds. 1992. Atmospheric deposition and forest nutrient

cycling. New York: Springer-Verlag. 707 pp.

Lefohn, Allen S.; Jackson, William; Shadwick, Douglas S.; Knudsen, H. Peter. 1997. 

Effect of surface ozone exposure on vegetation grown in the southern Appalachian

mountains: Identification of possible areas of concern. Atmospheric Environment 31(11): 

1695-1708.

Lynch, J.; Bowersix, V.; Grimm, J. 1996. Trends in precipitation chemistry in the United 

States, 1983-94 – An analysis of the effects in 1995 of Phase 1 of the Clean Air Act 

Amendments of 1990, Title IV. Unites States Geological Survey Open-File-Report 96-

0346.

Nodvin, S.; van Miegroet, H.; Linderg, S. [and others]. 1995. Acidic deposition,

ecosystem processes, and nitrogen saturation in a high elevation southern Appalachian

watershed. Water, Air, and Soil Pollution. 85(3): 1647-1652.

Peterjohn, W.; Adams, M. B.; Gilliam, F. S. 1996. Symptoms of nitrogen saturation in 

two central Appalachian hardwood forest ecosystems. Biogeochemistry 35: 507-522.

Southern Appalachian Man and the Biosphere (SAMAB). 1996. The Southern

Appalachian Assessment Assessment Atmospheric Technical Report. Report 3 of 5. 

Atlanta: U.S. Department of Agriculture, Forest Service, Southern Region. 84 pp.
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Appendix A

How the minimal nitrate and sulfate detection levels were calculated: According to 

Jim Lynch (Pennsylvania State University) the minimal detectable levels for sulfate and

nitrate in wet deposition collectors is 0.03 mg/liter. To detect an increase in deposition

(kg/ha) at a specific location depends upon the amount of rainfall. Rainfall modeling was 

conducted as a step in order to estimate the annual wet sulfate and nitrate deposition

(Lynch and others 1996). The estimated rainfall for the Class I area is 42 inches (1067

mm). The following equation was used to estimate the minimal detectable level of an

increase in sulfate or nitrate:

D = C * Rain * 0.01

where:

D = estimated deposition in kg/ha

C = the concentration of pollutant, which is 0.03 mg/liter

Rain = the rainfall in millimeters, which is 1067

The estimated deposition level for sulfate and nitrate is 0.3 kg/ha based upon using the

preceding equation. The George Washington and Jefferson National Forests receives

about 5 to 10 PSD applications per year. Therefore, the significant modeling screening

value is being reduced to 0.03 kg/ha to provide a margin of protection due to the number 

of PSD applications received over a 2 year period.