Dispersion Modeling

As discussed in Section 3.0 of this document, the study utilized the ISCST2 dispersion model. This model was chosen

because of its flexibility in analyzing a large variety of sources in an almost unlimited number of situations. Also, the model is

widely used and scrutinized by the EPA modeling community. As previously mentioned, a number of studies have been done identifying the model's performance over long and short distances.

Appendix B lists the ISCST2 input code used for the Weehawken study. As shown in the code, the urban mode plume dispersion

values were used, as well as default values of wind profile exponents and vertical potential temperature gradients. No downwash was calculated, and emission rates were assumed constant over the entire study period. The following sections describe the

special considerations applicable to the different types of

pollutant sources. The ISC2 User's Guide (Brode, 1992a) should be

consulted for further information about the source code.

4.2.1 Source/Emissions Information

4.2.1.1 Point Sources

Point sources were chosen and modeled based on information

obtained from the AIRS database. The ISCST2 model analyzed sources

located in Hudson and Bergen Counties in New Jersey, as well as New York County in New York City. The ISCST2 input file found in

Unfortunately, at the time of this study, AIRS reported

particulate data as total suspended particulate (TSP) for both New

Jersey and New York. To convert these values to a PMk, equivalent,

a conversion ratio of 0.485 (PMjo/TSP) was chosen based on the

studies by Rodes (1985) and Frank, et al. (1984). Although these

ratios are not site specific but were developed to convert TSP

pollutant concentrations to PMiq values at NAAQS monitoring sites,

the ratio was assumed to apply to the study area because of the

wide range of sources evaluated. Since most of these sources are

located outside the receptor area, the pollutants from all sources

should be well mixed and thus represent a typical urban airshed. EPA is currently updating the AIRS database to report particulate sources as PM,o, so this conversion should not be necessary in the future.

4.2.1.2 Volume Sources

All roadways were evaluated as volume sources for this analysis, and were divided into equivalent sections four times as

long as the road width. Although the ISCST2 user's guide

recommends that these segments only be twice the road width, the longer sections became necessary in order to limit the overall

number of sources to an amount the model could process. Thus, for

the determination of the initial horizontal dispersion parameter,

CTyo, the formula recommended in the guidance document was used:

2.15

26 where W represents the road width (in meters) . This equation still provided uniform dispersion to receptors located close to the source. For the determination of the initial vertical dispersion

parameter, a^, the empirical formula developed by the California

Department of Transportation (CALTRANS) for the CALINE3 model was

used (Benson, 1979):

where ATIM is the model averaging time (60 minutes for this study)

and,

o^ = 1.8+0.11 (TR) (11)

with.

TR = — (12)

where TR = residence time (sec) u, = wind speed (m/sec)

The residence time represents the period when the exhausted

pollutant remains in the mixing zone above the roadway. Thorough

mixing of the pollutant is assumed in this zone due to the buoyancy

and momentum of the exhaust gas and the wake effects from the

passing vehicles (Benson, 1979). For this analysis, the average

wind speed for the month of July (over the years 1985-1989) was

used to evaluate a^. Section 4.2.2 provides more detail on the

meteorological data.

Table 4-1 showed a listing of the traffic data used in the study. The New Jersey Department ^f Transportation and the Hudson

County (NJ) Engineering Department provided this data. The locations described represent the areas of traffic counts made in the last 5 years, which gives a good indication of the heavily

traveled roads in the area. Counts for Interstate 495 were

unavailable from either source. The ADT's along 1-495 were

estimated based on the traffic at the Lincoln Tunnel tollbooths

subtracted by the number of vehicles exiting and entering via the

ramps at Park Ave., Willow Ave., and Boulevard East (the Mueller

ramp). These ramps are the only major access points within the

study area before the ramp for J.F. Kennedy Blvd on the western end of the study area.

Average speeds along each road are estimated based on the

roadway type. Light duty city streets are given an average speed of 25 mph because these streets tend to carry local traffic

travelling short distances. Heavy duty city streets usually

average speeds of 35 mph because these tend to carry transient

traffic, yet, within cities, the speed limits are rarely over 35 mph. Due to the high traffic volumes in this region, highways

average speeds of 55 mph.

Road widths are estimated based on the information from the

USGS map. 2-lane roads are assumed to average 10 meters (approx. 30 ft) in width while 4-lane roads are estimated at 15 meters.

Interstate 495 is evaluated based on an average of 6-lanes (or 30

meters) throughout the study area.

Calculations of emission rates along each street section used

particulate emissions from mobile sources based on the regulatory

guidance in AP-42 (USEPA, 1985a). The program also accounts for particulate emanating from brake and tire wear. Since leaded fuel

is extremely uncommon, misfueling rates are set equal to zero,

leaving the lead content for both leaded and unleaded fuel at 0.014

g/gal. For further information on lead content. Table 2-2 of AP-42

should be consulted. Additional information on the calculation of

emission factors from mobile sources can be found in USEPA (1985b). The emission rates for all roadways evaluated in the study can be identified in the ISCST2 input code of Appendix B.

The Lincoln Tunnel and the surrounding toll booths presented a unique difficulty in modeling. To estimate the emissions from vehicles at the tolls, this section is modeled as an area source.

Average speed is assumed to be 5 mph beginning a distance of approximately 500 ft (150 meters) from the tollbooths. This average speed takes into account vehicle deceleration as cars approach the booths, and, more importantly, the starting and stopping which occurs as the vehicles queue at the booths. Since

the tolls are only located on the eastbound lanes (traffic entering New York City) , only this section was modeled as an area source

with an ADT of half the vehicles using the tunnel. The westbound

lanes were modeled similarly to the other roadways with an average speed of 45 mph (as vehicles accelerate from the 35 mph speed limit

in the tunnel to the 55 mph speed limit on 1-495) and a width of 15

meters. The stretch of road between the tollbooths and the tunnel

estimated based on a speed of 35 mph. Figure 4-2a provides details of the road network in the vicinity of the Lincoln Tunnel entrance.

Based on information from the New York/New Jersey Port

Authority (Calo, 1992) , an assumption was made that 80% of the

vehicle exhaust emitted in the tunnel was removed through the

tunnel's ventilation system, while the remaining 20% escaped

through the entrance portals. Thus, 10% of the total exhaust

emitted inside the tunnel exits through the portal on the New Jersey side. The amount of pollutant emitted is based on the tunnel's length and the particulate emission factor for vehicles cruising at 35 mph. Figure 4-2b is a diagram detailing the design of the tunnel. No correction was made for particle settling or deposition inside the tunnel since a large majority of the particulate exiting through the portals is emitted only a short distance from the entrance. Pollutants exiting through the portals is assumed thoroughly mixed within a distance of 50 meters from the entrance by vehicle wake effects both inside and outside of the tunnel.

Train emissions were not considered for this study. Since the West Shore Terminal (located in northern Weehawken) is no longer used and the Conrail and Amtrak lines in the area are diverted

underground through this region, the only rail line in the study

area is a short section of the Susquehanna and Western line which

FIGURE 4-2a - Schematic of the Lincoln Tunnel Entrance. All

labeled roadways are residential and not under the

jurisdiction of the New York/New Jersey Port Authority.

H.D&

?

Linccin Tunnel Entrance In Weetiawken, NJ r—»

FIGURE 4-2b - Design of a typical portal tube. As can be seen

in Figure b, the tunnel consists of three separate tubes: north/ central and south.

rtan m rut.

MM rm^t ͣ«>-

K#ri« TO •«<ͣ

Typical Pcrtal Crcss-Sectlcn fcr

4.2.1.3 Area Sources

There were no sources analyzed as area sources within the

study region with the exception of the portion of 1-495 in the

vicinity of the Lincoln Tunnel tollbooths as described in Section 4.2.1.2.

4.2.1.4 General Considerations

Temporal variations in source emissions were not represented

in this study due to lack of data. For point sources, reliability

of this information from the AIRS database is highly suspect. For

the volume sources, no data regarding daily changes in traffic

patterns was available from the highway departments.

4.2.2 Meteorology

Meteorological data was obtained from the National Climatic

Data Center (NCDC) in Asheville, NC through the EPA OAQPS Bulletin Board System for the Newark (NJ) International Airport station for the years 1985-1989. This station was chosen because of its

proximity to the study area, and the fact that this station is used

to evaluate data from the permanent NAAQS PMjq monitor in Union

City, NJ. The station is located approximately 10 miles to the

southwest of Union City, since this station only reports surface data, information on mixing heights was obtained from the Atlantic City (NJ) Regional Airport station. Although mixing heights are fairly uniform over large distances, these values may be slightly lower than the actual mixing heights found in the Newark area

because of the tendency for inversions to form in the summertime near shorelines. The most frequently occurring mixing height (550

meters) was used for the evaluation.

Appendix E shows the meteorological data used for the study. Figure E-1 shows the windrose encompassing the years 1985 through 1989, while Figure E-2 demonstrates the windrose obtained for the

month of July during the same years. The information used in

Figure E-2 was utilized to establish the probability of occurrence

of each of the 96 possible meteorological conditions (6 wind speeds in 16 directions). Changes in stability class were not evaluated to reduce the amount of input data required. The ISCST2 model

analyzed each meteorological condition separately as a specific

hour of meteorological data. Thus, each hour of meteorological

data actually represents one possible meteorological condition.

Since the ISCST2 model does not account for pollutant transport

times, one hour is sufficient to estimate the concentration effects

at each receptor site for a given set of meteorological conditions.

These values estimate a receptor site's average concentration value

over the entire month which establishes the rank of each grid

location.

The July, 1985-1989 meteorological data was used for this

analysis based on several factors. First, the field sampling

portion of this project was performed during July. Also, the

permanent PMjo monitoring site had historically measured its highest

pollutant concentrations during this summer month. Finally, five

years of data was evaluated to obtain a representative sample of

meteorological conditions experienced in the region. This reduces

the likelihood of non-representative input data due to possible non-normal events in a particular year. Figures E-3 through E-6 give the corresponding windroses for the years of 1985 and 1989, respectively. These figures show that the annual windroses are

similar, but change when analyzing only the month of July.

Therefore, a minimum of five years of meteorological data should be

used whenever possible.

4.2.3 Topography

The topography of the region is fairly level, except for

lowlands along the Hudson River to the east (in the Lincoln Harbor

and Port Arthur areas) and the beginning of the meadowlands to the west. According to figure 3-1, these regions have little to no

human population. In the main portion of the study area, the

overall elevation change is approximately 50 feet. Figure 4-1 shows the elevation changes within the region. Because of the level terrain in the populated portions of the study area, topography was not factored into the dispersion model.

4.2.4 Special Model Requirements

An output file was generated in order to use the SITE model to

establish the monitor locations. As shown in Appendix B and

described in Section 3.2.2, a "postfile" was generated through the OUTPUT pathway.

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