United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-84-070 Sept. 1984
Project Summary
Philadelphia Roadway Study
R. Burton and J. Suggs
The primary objective of this study
was to collect participate mass
concentration data to define vertical
and horizontal distances from
roadways required for inhalable
particulate (IP) monitor siting.
Secondary objectives were to compare
the particulate mass measurements to a
simple model which considers both
dilution and settling of particulate
matter and to determine if the siting
criteria for inhalable particulate matter
(<15 fjm} applies to lead (Pb)
measurements made with an IP
sampler.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
Existing guidelines for siting TSP
samplers near roadways are contained in
Federal Register Methods Vol. 44, No. 92,
May 10, 1979. For ambient 24-hour
general population exposure and
surveillance monitoring a sampler set too
close to any localized source such as a
heavily traveled roadway would
overestimate the level of TSP for the
general surrounding area.Theguidelines
restrict sampling closer to the roadway
than 25 m at a two m height and five m at
a 15 m height. A straight line connecting
these two points defines the restricted
boundary.
The development and implementation
of a size-specific ambient particulate
standard instead of the current Total
Suspended Particulate standard will
require additional information on howthe
various size fractions of particles disperse
in the area surrounding a major roadway.
The information would be usedto replace
the criteria for TSP sampling.
Since the rate of deposition and vertical
diffusion depends upon particle size, the
criteria for TSP cannot be assumed to
apply to both the larger coarse (2.5 up to
10 or 15 pm) particles and the smaller
fine (<2.5 yi/m) fraction. Smaller particles
are assumed to deposit from the atmos-
phere much slower than the larger ones,
with the very small submicron size parti-
cles behaving nearly as a gas. Assuming
no reaction, pollutant gases tend to
decrease in concentration away from the
source because ^i dilution. Suspended
particles are i educed in concentration by
both dilution and deposition.
Experimental Procedures
Approach
The approach was to collect the fine
and coarse particulate mass fractions at
one point upwind, one point in the center,
and nine points directly downwind of a
major roadway when the wind direction
was within a 90 degree sector centered
about the perpendicular to the road.
Horizontal distances are referenced from
the edges of the 60 m wide roadway
unless otherwise noted. Likewise, verti-
cal distances are referenced from ground
level. These data could then be used to
construct concentration isopleths. The
upwind sampling site was used for
estimating the background concentra-
tions. A sampling site was located in the
roadway median on the perpendicular to
verify the maximum concentrations
extrapolated from the roadside
measurements. Sierra Model 244E
Dichotomous S3mplers with 15 fjm
inlets were used for collecting the fine
and coarse fractions on 37 mm teflon
filters. The dichotomous samplers were
operated in accordance with procedures
of the Inhalable Particulate Network
(IPN). The particle separation
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characteristics of the sampler are based
on aerodynamic particle size which
transforms the actual diameter to the
equivalent diameter of a unit density
sphere having the same settling velocity
as the particle in question of whatever
shape and density. All particle sizes
referred to in the report are aerodynamic
diameter. Sampling was initially
performed (Phase I) at ground level two m
height above the doorway to determine at
what point downwind the concentration
had been reduced by upwind diffusion
and particle deposition to approximately
the background level. Sampling in the
vertical direction was then conducted
using two towers -- one located at road-
side five m downwind, and the other
approximately half-way downwind from
roadside to the point at which the
roadway particulate mass concentrations
had dropped to within 10% of background
level. The half-way point was found to be
approximately 25 m downwind.
Meteorological measurements for
wind speed, wind direction, temperature
and humidity were made from a 15 m
height at the monitoring site located 5 m
downwind of the roadway. A Climatron-
ics electronic weather station was used
to acquire the data on strip chart
recordings.
Based on historical meteorological data
for the area, particle sampling was
initiated in March, 1982, to obtain the
downwind particle concentration
gradient under wind direction conditions
that were expected to be primarily
perpendicular within ±45° of the road-
way. In order to minimize variations in
wind speed and direction during particle
sampling, sampling periods of "accept-
able" meteorology were limited to a 14
hour (7:00 AM - 9:00 PM) daytime sam-
pling period. With this schedule the early
morning inversions, wind instability and
the night time low traffic count were
eliminated.
Based on data from an earlier study,
sampling was only conducted when wind
speeds were above two mph and wind
directions within ±45° of the freeway
perpendicular. Wind speeds below two
mph do not provide adequate transport to
define a profile. Wind directions
perpendicular within ±45° were
expected to provide ratios of downwind to
upwind concentrations exceeding at least
a factor of two.
A Climatronics Wind Controller (Model
WMIII - PN100864) activated by wind
speed and direction sensors limited
sampling to periods when parameters
were within preset specifications. The
2
statistical study design recommended at
least 10 valid sample runs for the
horizontal configuration and 10 for the
vertical configuration. A sample run was
required to last for at least four hours in
order to have adequate mass collection
on each dichotomous sample filter.
The number of vehicles operating on
the roadway during the study was very
important. Any large fluctuations in
traffic count would affect the particle con-
centration levels (and hence the iso-
pleths) around the study site. Mechanical
car counters were used to obtain real
time hourly traffic counts. Daily traffic
flows ranged from 2119 to 3906 vehi-
cles/hour during sampling periods
(average = 3177 + 460). The 7:00 AM -
9:00 PM sampling period had a
reasonably constant traffic density during
this time period.
Site Location and Description
The study was conducted in Northeast
Philadelphia at Roosevelt Boulevard
between South Hampton and
Woodhaven Roads. Roosevelt Boulevard
serves as one of the two major north-
south traffic arterials for the city.
Preliminary meteorological monitoring
and review of historical data indicated that
winds could be expected to flow across
the roadway into the sampling cross-
section at least 80% of the days allotted
for the study. The sampling cross-sec-
tions were located on the grounds of the
Pennsylvania State Hospital where the
upwind and downwind sites were on
open grass covered fields extending more
than 1200 meters from the roadway in
both the upwind and downwind direc-
tions. The sampling site reach was
without interfering buildings and service
roads for approximately 3500 m along the
roadway. The location was within two
miles of an EPA Inhalable Particulate (IP)
Network site which averaged 33 /vg/m3
for IP mass during the period March,
1980 through May, 1981.
Sampling Scheme
Particulate sampling points on the
roadway perpendicular were located 220
m upwind, the roadway median, five, 25,
75, 125, and 175 m downwind during
Phase I sampling. After 12 sample runs
were completed for Phase I, the
dichotomous samplers were relocated for
vertical, Phase II sampling. Towers were
used for elevating the dichotomous
samplers to seven and 15 m heights.
Samplers were located at 220 m upwind
(two m elevation), the roadway median
(two m elevation), five m downwind (two,
seven, 15 m elevations), and 25 m (two,
seven, 15m elevations). Sampling was
begun simultaneously at each of the
seven points located on the roadway
perpendicular if the wind speed and
direction were within acceptable limits. A
collocated sampler at the 25 m downwind,
two m height sampling site was operated
throughout the study to obtain precision
data. Sampler flow checks were made
daily, and a performance audit completed
to verify that the calibrations had not
changed during the study.
Sample Analysis
The dichotomous coarse and fine
fraction samples were analyzed
gravimetrically for mass concentration.
Lead and bromine concentrations were
determined by energy dispersive X-Ray
Fluorescence. The analysis procedures
used for the IP Network, Standard
Operating Procedures for the X-Ray Flu-
orescence Analysis of Multielements on
Dichotomous Sample Filters,EMSL-RTP-
SOP-EMD-010, November, 1981, were
followed.
Results and Discussion
Twenty-four sample runs were com-
pleted between March 5, 1982 and May
7, 1982 with an average sample time of
10.3 hours. Eight horizontal and ten
vertical sets of samples (complete at all
sampling points) were used for defining
the horizontal and vertical particulate
mass concentration gradients. In
addition, horizontal profiles were
obtained on two days immediately
following "salting" of the roadway to
prevent icing. These data were not
included in the general statistical
analysis but are described separately.
Horizontal Profile
Average downwind concentrations
(/jQ/m3) of fine, coarse, and total (coarse
+ fine) particles for mass and lead mass
were examined as a function of distance
(m) from the highway. Concentrations
measured at ground level (two m height)
were averaged over eight days of
sampling at each of six downwind and
one upwind sites. The sampling days
cover a range of hourly traffic densities
from 2160 to 3906 vehicles with wind
speeds ranging from 5.8 to 18.5 mph.
Based on the concentration measured
five m downwind of the roadway edge,
the average maximum increases above
background (at two m height) in particu-
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late mass and lead concentration down-
wind of the roadway were:
Phase I Phase II
Coarse mass
Fine mass
Total mass
Fine lead
Coarse lead
Total lead
Wind speed (mph)
4.6
2.6
7.2
0.47
0.08
0.55
11.2
8.5
4.8
13.3
0.48
0.11
0.59
8.4
The coarse particulate mass concen-
tration at the two m elevation increases
from the roadway centerline to five
meters downwind and then decreases
with distance while the fine particulate
mass decreases with distance immedi-
ately from the centerline. The total mass
decreases with distance from the
centerline. A significant contribution is
made to the coarse fraction from
pavement wear and particle re-entrain-
ment, which contribute little to the fine
fraction. This fact and the effect of
atmospheric turbulence probably
account for the difference in concentra-
tion profiles for the different size fractions
of the mass.
Logarithmic equations fitted by least
squares methods were used to
empirically describe (for distances
between five m and 175 m downwind of
the roadway edge) the relationship be-
tween the horizontal two m mass concen-
tration (C) in fjg/m3 and distance (D) in
meters downwind as follows:
Standard
error of
Correlation estimate
Fraction Equation Coefficient (//g/m3)
Coarse mass C = 17.56 - 0.990 0.40
1.71 InD
Fine mass C= 18.82- 0.964 0.53
.99 In D
Total mass C = 36.378 - 0.990 0.66
2.71 In D
The coefficients show good correlation of
C and In D. Setting the equations equal to
background concentration and solving for
distance, the downwind point at which
levels reach background were
determined. These distances are 74 m
(coarse), 87 m (fine), and 77 m (total).
Correlation coefficients between traffic
density and mass concentration for each
particulate size fraction (fine and coarse)
were calculated for each of the six
downwind ground level sampling
stations. Statistically significant
correlation at the 90% probability level
occurred for fine mass and traffic at 5 m
downwind and at the roadway. No other
correlations between particulate mass
fractions and traffic density were found at
the 90% probability level apparently due
to the limited range of traffic densities
present during the study. Correlations
between wind speed and fine particulate
mass were statistically significant at the
90% probability level for all sites. In the
case of the coarse fractions none of the
sites correlated with wind speed except
for the site five m downwind at a height of
seven m. Total mass correlated with wind
speed at the 90% probability level for all
sites except at 175 m downwind.
Lead mass concentration averages also
were plotted versus horizontal distance
downwind. The lead concentrations
decrease with distance from the roadway
with the highest concentrations
occurring at the center of the roadway
(0.17 fjg/.m3 coarse, 0.60pg/m3 fine, and
0.78 fjg/m3 total). The concentrations for
total and fine fractions remain signifi-
cantly above background for at least 175
m downwind. The lead concentration
apparently does not dilute vertically at the
same rate as the fine mass mode. Loga-
rithmic equations fit by least squares to
empirically describe the deposition and
vertical diffusion are given as follows (for
distances between five m and 175 m
downwind of the roadway edge):
(C = mass concentration, jug/m3; D = dis-
tance downwind, m)
Standard
error of
Correlation estimate
Fraction Equation Coefficient (//g/m3)
Coarse Pb
Fine Pb
Total Pb
C = .187-
.029 In D
C = .715 -
.106 In D
C = .903 -
.135 In D
0.985
0.990
0.990
.095
.032
.032
The correlation between traffic density
and lead concentrations for the fine size
fraction were significant at the 90%
probability level for all ground level sites
except 175 m downwind. Correlations
between fine lead and wind speed were
found for all sites at the 90% probability
level. The correlation between coarse
lead and traffic density was significant at
the 90% probability level only for sites at
five m, 25 m, and 75 m downwind. Coarse
lead and wind speed correlations were
significant at the 90% probability level at
all downwind sites except for five m and
25 m at a height of seven m. Wind speed
was a more dominant factor than traffic
density in determining both mass and
lead concentration levels over the range
of conditions encountered.
Vertical Profile
Vertical profiles for mass and lead in
each particle size fraction were first
examined by plotting the average
concentration for 10 sample runs versus
heights of two m, seven m, and 15m
based on measurements from towers
located at five m and 25 m downwind.
Background measurements were made
at the two m height.
Mass concentrations measured at the
two tower locations and upwind at a two
m height were averaged over 10 days of
sampling at each of the six tower
locations. The coarse particle concentra-
tions were statistically different from two
m background (95% probability level) only
at the ground level locations. Fine
particulate mass was significantly
different from two m background for at
least 15 m vertically at the 25 m
downwind site and at least seven m
vertically at the five m downwind site.
Total particulate mass measured at
heights above ground level (two m) were
found to be significantly different from
two m background for only the seven m
vertical at the five m downwind location.
The vertical gradient mass data was not
fit to empirical equations since it was at
background level at some of the elevated
measuring points.
In the vertical profiles, lead concentra-
tions for fine and total particles were
significantly different from background
up to 15 m vertically for both downwind
towers. Coarse lead was significantly
above background for at least seven m
vertically at both downwjnd towers.
No significant correlations were found
between composite mass fractions and
traffic density at the elevated sites. The
same was true for the lead fractions.
Wind speed correlated with fine mass at
the 99% probability level for all sites
except the five m downwind, 15m height
site. Coarse particle mass fractions corre-
lated significantly with wind only at the
five and 25 m downwind sites at the
seven m height. Coarse lead fractions
correlated significantly only at the 15m
height at five m and 25 m downwind. Fine
lead showed a significant correlation
with wind speed at all sites.
Since fine and total lead concentra-
tions were above background up to a 15 m
height, logarithmic equations as follows,
were fitted by least squares to empirically
describe the vertical dilution, (C = mass
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concentration, /ug/m3; H = distance
above ground, meters):
Fraction
Fine lead
(5m dw)
Total lead
(5m dw)
Fine lead
(25m dw)
Total lead
(25m dw)
Equation
C = 0.674 -
0.222 In H
C = 0.833 -
0.273 In H
C = 0.498 -
0.145 In H
C = 0.609 -
0.1 77 In H
Correlation
Coefficient
0.990
0.990
0.998
0.998
Standard
error of
estimate
(//g/m3)
0.030
0.057
0.013
0.008
Bromine/Lead Ratios
The Br/Pb ratios found to exist in the
downwind roadway particulate matter
were consistent with ratios reported in
the literature. As described by Harrison
and Sturges, the major particulate
species of exhaust lead and bromine in
the United States is PbBrCI and should
give a Br/Pb mass ratio of 0.386 in the
exhaust. The average Br/Pb ratio for all
ten downwind monitoring locations was
0.36 ± .06 in the fine fraction and 0.55 ±
.26 in the coarse fraction. Eighty percent
of the lead mass was found in the fine
fraction.
Development of Empirical
Model for Roadway Generated
Particulate Levels
Rodes and Holland developed an
expression in the Los Angeles Catalyst
Study which predicts (for two m height)
the exponential horizontal decrease of an
initial concentration of an inert gas
measured at a given point downwind of
the centerline of a roadway. This
approach was used to develop an
equation for computing particulate and
lead mass concentration at heights up to
15 m above ground level and distances
between five m and 175 m downwind of
roadway edge for cross-wind cases at
wind speeds between three and six
mph. Rodes and Holland's equation is
C = C
"Hr 1+c"
Where C = mass cone, at distance
downwind (/jg/m3)
C26 = mass cone, at initial
point downwind 26 m from
roadway centerline (/yg/m3)
B, = "vertical" dilution parameter
X = distance downwind from center-
line (m) where 26M
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confidence level also were found for the
lead component of the mass fractions.
Within wind speed and traffic density
boundaries of the study, the downwind
mass gradients in the vertical and
horizontal directions were predictable
from an empirical relationship.
Therefore, zoning graphs for use in
developing siting constraints were
obtainable for the mass and lead
fractions. The bromine/lead ratio was
found to be consistent with other studies
indicating that the increased lead mass
levels were generated from the roadway.
The criteria for siting TSP samplers
(presently in the Federal Register) cannot
be used for siting IP samplers since the
constricted area is not bounded by a
straight line as given in the TSP criteria.
The area is bound by an exponential
function with respect to height and dis-
tance. The downwind mass and lead
concentration profiles for each size
fraction measured are similar in shape
but extinction rates vary considerably for
the different fractions measured.
The paniculate mass settling rate
(deposition) downwind to a distance of
175 m is not significant. The downwind
horizontal decrease in particulate
concentration at a height of two m is due
mostly to the upward diffusion of the
particles. Only 1.2% of the fine mass is
lost between five m and 25 m downwind
at a height up to 15 m. The coarse mass
decreased 9.7% at the same height and
over the same distance. One cannot
assume that correct siting can be
accomplished by placing the sampler at a
greater height, sincetheplume rises with
distance downwind. The downwind
dilution rate of lead associated with the
fine fraction is different from that of the
fine or coarse mass fraction. Most of the
lead remains below a height of seven m
vertically, and is significantly above zero
at a distance of 175 m downwind.
It was possible to empirically derive two
dimensional exponential equations
describing dilution of mass and lead con-
tent in both the horizontal and vertical
directions downwind which account for
greater than 90% of the variability in the
data. The equations are of the form used
to describe dilution of an inert gas.
However, the exponents in the fitted
equations are not in agreement with the
values found previously. The dilution rate
is highly influenced by the difference in
concentration upwind and that directly
downwind of the source.
P. Burton (also the EPA Project Officer, see below) and J. Suggs are with
Environmental Monitoring Systems Laboratory, U.S. Environmental Protection
Agency, Research Triangle Park, NC 27711.
The complete report, entitled "Philadelphia Roadway Study," (Order No. PB 84-
226 927; Cost; $8.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park. NC27711
. S. GOVERNMENT PRINTING OFFICE: 1984/759-102/10672
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