The Existence of Complex Wind Fields 

in the Region Surrounding the 

Portland Power Plant Site 

and the Use of CALPUFF 

February 25, 2010 

Bureau of Technical Services 

Division of Air Quality 
New Jersey Dept. of Environmental Protection 

Section 1. INTRODUCTION 

This document discusses technical issues related to the use of the CALPUFF modeling system to 

model the impact of emissions from the Portland Generating Station on New Jersey. The use of 

CALPUFF for near-field regulatory applications involving “complex winds” is addressed in 

Section 7.2.8(a) of the EPA’s Guideline on Air Quality Models (EPA, 2005). 

“a. Inhomogeneous Local Winds. In many parts of the United States, the ground is neither flat 

nor is the ground cover (or land use) uniform. These geographical variations can generate local 

winds and circulations, and modify the prevailing ambient winds and circulations. Geographic 

effects are most apparent when the ambient winds are light or calm. In general these 

geographically induced wind circulation effects are named after the source location of the winds, 

e.g., lake and sea breezes, and mountain and valley winds. In very rugged hilly or mountainous 

terrain, along coastlines, or near large land use variations, the characterization of 

the winds is a balance of various forces, such that the assumptions of steady-state straight-line 

transport both in time and space are inappropriate. In the special cases described, the CALPUFF 

modeling system (described in Appendix A) may be applied on a case-by-case basis for air 

quality estimates in such complex non steady-date meteorological conditions. The purpose of 

choosing a modeling system like CALPUFF is to fully treat the time and space variations of 

meteorology effects on transport and dispersion. The setup and application of the model should 

be determined in consultations with the appropriate reviewing authority (paragraph 3.0(b)) 

consistent with limitations of paragraph 3.2.2(e).” 

In a 2008 memorandum issued by EPA (EPA, 2008), EPA indicated that to use CALPUFF for 

near field applications, there should be a determination that complex wind fields exist at the 

location of the modeling. EPA also indicated that the treatment of complex winds is important 

when estimating design concentrations. This guidance appears applicable only to the use of 

CALPUFF under Condition 3 in paragraph 3.2.2(b) of the Guideline regulations and the 

subsequent requirements listed in paragraph 3.2.2(e). Justification for use of CALPUFF in the 

near-field here is based on Condition 2 in paragraph 3.2.2(b) of the Guideline regulations (where 

a validation study demonstrates that an alternate model performs better), not Condition 3. 

Regardless, this report demonstrates the existence of complex wind flows in the Portland Power 

Plant air shed and their importance when modeling emissions from this facility. The existence of 

complex winds in this area is an additional reason that the use of CALPUFF is appropriate here. 

Section 2 COMPLEX WIND DETERMINATION 

Section 2.1 Local Terrain Features 

In Figure 1 the elevation of the terrain in the immediate vicinity of the plant is shown. Terrain 

with elevations above the top of the 400 ft stacks venting Units 1 and 2 (694 ft amsl) is located as 

close as 2 km to the east and to the southeast of the stacks. In addition, the very high terrain on 
Kittatinny Ridge that exceeds 1500 ft amsl is located to the north and northwest as close as 7 km 

from the stacks. 

Several 2008 aerial photos have been included in this report to provide a greater understanding 

of the region’s terrain. Photo 1 shows the Portland Power Plant in the foreground and the 

surrounding terrain looking in a northwesterly direction towards Kittatinny Ridge. The higher 

terrain immediately to the east of the Portland Power Plant in New Jersey and the curvature of 

the Delaware River Valley are also apparent. Photo 2 is a view of Portland Power Plant through 

the Delaware Water Gap in Kittatinny Ridge. Photo 3 shows the Portland Power Plant in the 

foreground, the nearby terrain that exceeds stack top just across the Delaware River to the 

southeast of the plant, and in the background are Jenny Jump and Scotts Mountains, significant 

terrain features with elevations over 1,000 ft amsl. The last photo, Photo 4, was taken looking 

south. The Portland Power Plant is in the foreground and the Martins Creek Power Plant, which 

is located approximately 7.5 miles south of Portland Power Plant, is in the background. These 

photos clearly show that there are significant terrain features near Portland Power Plant. These 

terrain features generate the non-steady state wind fields that affect the transport and dispersion 

of plumes emitted from the Martins Creek and Portland Power Plants. 

Section 2.2 Meteorological Measurements Collected Near the Portland Site 

While not capturing the full three-dimensional local terrain and mesoscale wind fields, wind 

measurements taken at one location near the Portland site can be of use in demonstrating the 

existence of non-uniform vertical wind fields in and near Portland and the Delaware River 

Valley. From July 1993 through June 1994, meteorological data was collected near the Portland 

Generating Station. This monitoring program consisted of a collocated 100-meter tower and 

Doppler SODAR. Tower measurements of wind direction and wind speed are available at 30 and 

100 meters. The sodar provided wind direction and wind speed for modeling purposes at 30-

meter increment levels from 120 meters up to 510 meters. The monitoring program is described 

in detail in Appendix A. 

As can be seen in Figure 3-1 of Appendix A, the measurement site is located 2.3 km west of the 

power plant site on terrain above the river valley at an elevation of 610 ft amsl. The stack base 

elevation of the Portland Power Plant stacks is 294 ft amsl. Wind roses were generated from 

wind measurements taken at three heights. Figure 2 shows the 30 meter wind rose from the 

meteorological tower. Figure 3 shows the 150 meter SODAR winds. Figure 4 shows the 300 

meter wind rose. 

When examining these figures, the expected increase in wind speed at the higher levels is 

evident. However, there are also some obvious differences in wind direction that occur at the 

three levels. The lower 30-meter level data clearly shows a much greater frequency of winds 

from the north/north-northeast and south than that which occurs at the 150 and 300 meter levels. 

This generally north/south wind flow reflects the general north-south axis of the Delaware River 

at that location. At 150 meters, the winds reflect the occurrence of larger-scale, westerly synoptic 

winds and with an additional peak wind direction out of the northeast. This northeast wind 

direction peak is likely due to the influence of Kittatinny Ridge and its southwest to northeast 
orientation. In the 300 meter wind rose the synoptic winds out to the south-southwest through 

north-northwest are even more evident. 

In addition to vertically and horizontally varying winds, other meteorological conditions of 

interest at the site are the near stagnation condition that accompanies wind flow reversals near 

mid-days, especially in the summertime. As specifically mentioned in paragraph 7.2.8(a) of the 

Guideline on Air Quality Modeling Analysis (EPA, 2005), “geographic effects are most apparent 

when the ambient winds are light or calm.” Examination of the 150 meter SODAR winds 

provide a measure of the winds that directly impacting plumes emitted from Portland Power 

Plant. Winds measured at this height (1102 ft amsl) are 400 ft above the top of the stacks. At this 

level, very low wind speeds less than 2 m/s occur 8.5 percent of the time. Wind speeds of less 

than 2.5 m/s occur over 12.8 percent of the time. An example of a vertical wind profile during 

such a low wind, stagnation episode is given in Table 1. The table shows the extreme variation in 

wind direction with height that occurred at these times. There is roughly a 180 degree wind shift 

moving from the lower levels of the atmosphere to the higher levels during both hours. 

Table 1. Example of Profile Wind Direction/Speed Data Collected 

 at the Portland Site (Hours 11 and 12, July 18, 1993) 

Portland Site a 

Hour 

Height of 

Measurement 

above ground 

(m) 

Wind Direction 

(deg.) 

Wind Speed 

(m/s) 

10 ND ND 

30 274 1.74 

90 291 1.61 

120 257 0.77 

150 247 0.68 

180 253 0.50 

210 284 0.24 

240 328 0.32 

270 336 0.33 

300 35 0.49 

330 47 0.82 

360 46 1.15 

390 52 1.21 

420 63 1.25 

450 58 1.24 

480 45 1.15 

11 

510 36 1.06 

10 ND ND 

30 213 1.65 

90 217 1.56 

120 295 0.63 

150 312 0.76 

180 327 0.79 

12 

210 343 0.82 
Portland Site a 

Hour 

Height of 

Measurement 

above ground 

(m) 

Wind Direction 

(deg.) 

Wind Speed 

(m/s) 

240 5 0.75 

270 17 0.61 

300 26 0.48 

330 33 0.38 

360 16 0.34 

390 31 0.38 

420 35 0.41 

450 43 0.52 

480 40 0.45 

12 

510 45 0.58 

a. Measurement site on valley ridge 610 ft amsl. 

ND = No data 

Section 2.3 Meteorological Measurements Collected Near the Martins Creek Site 

Meteorological data was collected from May 1, 1992 through May 19, 1993 near the Martins 

Creek Power Plant. As can be seen in Figure 5, Martins Creek is located approximately 7.5 

miles south of the Portland Power Plant. It is in the same Delaware River Valley air shed as 

Portland Power Plant and therefore meteorological measurements taken at that location should be 

helpful in understanding the complex wind fields of the area. 

The SODAR and 10 meter tower wind speed and wind direction data was taken at the AMS-4 

site (see Figure 5). The AMS-4 site is located 2.5 km to the west-southwest of the Martins Creek 

Power Plant. AMS-4 is within the Delaware River valley at a base elevation of 320 feet. The 

SODAR data consists of wind speed and wind direction at 30 meter height increments from 90 

meters to 420 meters above-ground. 

Wind measurements were also taken at the AMS-8 meteorological tower. AMS-8 is located 6 km 

to the northwest of the Martins Creek facility and 10.6 km southwest of the Portland Power Plant 

(see Figure 5). It is on the valley ridge to the west of the Delaware River at a base elevation of 

810 feet. At AMS-8, tower temperature, wind speed and wind direction were collected at the 10 

meter level. 

Examining wind roses generated from this data can provide a better understanding of the 

complex wind flows within the Delaware River Valley. Figure 6 contains a wind rose of the 10 

meter AMS-4 data collected between May 1, 1992 and May 19, 1993. Not surprisingly, these 

low-level winds in the valley show a pronounced up-valley/down valley (northeast/southwest) 

flow. The SODAR data from the 150m level at AMS-4 is shown in Figure 7. The 150 meter 

SODAR level (840 ft amsl) is approximately equivalent in height above mean sea-level to the 
following: the height of the AMS-8 10 meter meteorological data, the height of the valley ridge 

running along the west of the Delaware River, and 150 ft above the top of the stacks that vent 

Units 1-2 at Portland Power Plant. Winds at the 150m SODAR level still show a strong terrain 

influence and the resulting up-valley/down valley winds. The 150 meter SODAR data collected 

to the west of the Portland Power Plant (Figure 3) shows much more frequent west and northwest 

winds. 

The 300m SODAR wind rose from AMS-4 (shown in Figure 8) displays more of a synoptic 

pattern. Winds at this level, 1300 ft amsl, are just above the highest peaks to the east of the 

Delaware River Valley. A modest frequency peak of winds from the northeast indicates much 

less of a valley influence than at lower levels. However, at the 300 meter level west of the 

Portland Power Plant site (Figure 4) there is almost no indication of a similar valley influence. 

The final wind rose in Figure 9 summarizes the 10 meter wind speed and direction data from 

AMS-8 (810 ft amsl). While taken at the same height above ground as the AMS-4 10 meter data 

(Figure 6), these winds show little of the in-valley influence shown at AMS-4. The lower level 

winds at the AMS-8 ridge location more closely resemble the regional, synoptic wind direction 

distribution shown in Figure 8. 

 

These seven wind roses combined (Figures 2 through 4 and 6 through 9) illustrate a wind field 

that varies dramatically in both the vertical and horizontal directions in the Delaware River 

Valley air shed where Portland Power Plant is located. 

The sulfur dioxide monitoring data collected from May 1, 1992 through May 19, 1993 also 

indicate that low wind speed/near stagnation meteorological conditions of concern because of the 

high concentrations that result. Figure 5 shows the network of eight SO2 monitoring stations 

where measurements were collected. These monitors are identified as AMS-5, AMS-7, AMS-8, 

AMS-9, AMS-10, AMS-11, AMS-12, and AMS-13. 

The meteorological conditions that occurred when the highest 1-hour SO2 concentrations were 

measured at these monitors was investigated. Network wide, 12 of the 15 highest 1-hour SO2

concentrations monitored occurred when the 150 meter SODAR wind speed was less than 2.5 

m/s. The 150 meter SODAR wind speed was less than 2.5 m/s for more than half of the top 20 1-

hour SO2 concentrations monitored at each of these sites. This supports the concern that high 

impacts occur during light wind speeds when geographic effects on the wind field are most 

apparent. 

Section 3 DIFFICULTIES WITH MODELING NEAR-FIELD IMPACTS USING 

AERMOD 

AERMOD is EPA’s recommended refined model for traditional point sources. As noted earlier, 

AERMOD is a steady-state (straight-line) plume model. A critical limitation of a steady-state 

model is its inability to respond to terrain-induced spatial variability in wind fields or to changes 

in dispersion conditions resulting from changes in surface characteristics. When transporting and 

dispersing a plume from a stack, AERMOD uses a spatially invariant wind field (the entire 

modeling grid is assumed to have one wind direction in both vertically and horizontally). The 

straight-line plume transport used by AERMOD is based on the wind observations from a single 
location. Unlike CALPUFF, a variable or curved trajectory by the plume is not possible. 

Therefore, as a steady-state model, AERMOD cannot represent the three-dimensional variability 

in the meteorological fields, will not treat stagnation, will not track plume (puff) transport over 

time, and cannot assess the impact of wind reversals. Accordingly, AERMOD is not appropriate 

for modeling impacts from Portland’s emissions given low/variable wind episodes and complex 

vertical and horizontal wind fields discussed in the previous section. 

AERMOD will not account for the time required for the plume to reach a receptor and will not 

track the plume over several hours. Therefore, wind reversals that bring the previously emitted 

plume back into an area of concern as well as puffs that linger in the vicinity of the plant over 

several hours during stagnation conditions would be ignored. In an hours travel time the plume 

will only be transported 2 km from the stack when wind speeds are 0.6 m/s, and only 1 km from 

the stack when the wind speed is 0.3 m/s. 

Another concern about using AERMOD to quantify the impacts from the Portland Power Plant is 

the lack of a representative meteorological data set needed for such modeling. There is only a 

very limited set of meteorological data measurements taken near the Portland Generating Station. 

This data was collected from July 1993 to June 1994. The meteorological site was designed to 

collect data for the CTDMPlus model. 

Guidance on the requirements of meteorological data used in AERMOD is given in Appendix A. 

Section 8.3.c of the Guideline on Air Quality Models (EPA, 2005). It states: 

“Of paramount importance is the requirement that all meteorological data 

used as input to AERMOD must be both laterally and vertically representative 

of the transport and dispersion within the analysis domain.” 

Measurements of the meteorological conditions taken at a single point 2.3 miles west and 316 ft 

higher than the Portland Power Plant site will not reflect the three-dimensional local terrain and 

mesoscale winds, temperature, and stability variations in the modeling grid near the Portland site. 

Section 4 ABILITY OF CALPUFF TO MODEL NEAR-FIELD IMPACTS 

In this application, CALPUFF is used because it has the ability to treat certain important 

complex flow and dispersion conditions in a more refined way than other regulatory models. In 

the near-field, CALPUFF contains three important features that allow a refined treatment of 

impacts. One is the ability of CALPUFF to account for spatial variability in meteorological 

conditions such as wind speed and direction, stability, and temperature gradient variations over 

the domain. In complex terrain, winds often change dramatically over short distances. When 

performing near-field analyses in such conditions, the use of a model such as CALPUFF 

provides advantages due to its ability to represent complex spatially varying flow conditions with 

variable and curved plume trajectories. Steady-state (straight-line) plume models such as 

AERMOD cannot represent the spatial variability in the meteorological fields due to 

AERMOD’s steady-state assumption. 
The second important feature of the CALPUFF model is its ability to track emissions during 

stagnation and light wind speed conditions. In valley situations, nocturnal temperature 

inversions often develop that can trap pollutants released over several hours. CALPUFF allows 

pollutants emitted under such conditions to be tracked. Steady-state models do not allow for 

emissions during periods other than the current hour to be considered in the calculation of 

concentrations. 

REFERENCES

Environmental Protection Agency, 2005: Guideline on Air Quality Models. 40 CFR Part 51, 

Appendix W. Published in the Federal Register, Vol. 70, No. 216, November 9, 2005. 

Environmental Protection Agency, 2008: Technical Issues Related to CALPUFF Near-field 

Applications, memorandum from Roger Brode and Brett Anderson, dated September 26, 2008. 
Figure 1. Terrain and Land Use near the Portland Power Plant (located 

at center of map) 



Figure 5. Location of Portland Power Plant, Martins Creek Power Plant, 

Meteorological Stations AMS-4 and AMS-8, and the Eight SO2 Monitoring Sites 
 
 
 
 
Photo 1. The Portland Powr Plant Looking in a Northwesterly Direction towards. 

Kittatinny Ridge 
Photo 2. View of Portland Power Plant through the Delaware Water Gap in 

Kittatinny Ridge
Photo 3. The Portland Power Plant with the Nearby High Terrain across the Delaware 

River to the Southeast and Jenny Jump and Scotts Mountains in the Background 
Photo 4. Looking South, Portland Power Plant in the Foreground and the Martins Creek 

Power Plant in the Background
APPENDIX A 

Location of Portland Power Plant’s 

Meteorological Data 
The following figure was taken directly from the document: SO2 NAAQS Compliance Modeling 

Protocol for GPU’s Portland Generating Station, prepared for GPU Genco, prepared by ENSR 

Corporation, April 1999. 

Figure 3.1 Location of the Meteorological Site relative to Portland Power Plant