United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-94/191 November 1994
EPA Project Summary
Lake Michigan Urban Air Toxics
Study
Gerald J. Keeler
During the summer of 1991, an air
toxics monitoring program was con-
ducted in the lower Lake Michigan area.
This study, designated the Lake Michi-
gan Urban Air Toxics Study (LMUATS),
was designed to take advantage of the
intensive meteorological database be-
ing generated concurrently by the Lake
Michigan Ozone Study (LMOS). Inte-
grated 12-hour atmospheric samples
were collected daily from July 8 through
August 9, 1991, at three ground sites
(two collocated with LMOS stations). A
research vessel and a small aircraft
were deployed on selected days to mea-
sure micrometeorological parameters
and pollutant concentrations at offshore
locations near Chicago. Over 1,200
samples were collected and analyzed
to determine atmospheric levels of
polychlorinated biphenyls (PCBs),
pesticides, polycyclic aromatic hydro-
carbons (PAHs), volatile organic com-
pounds (VOCs), particle mass, and
trace elements.
In addition, Nuclear Activation Analy-
sis and Scanning Electron Microscopy
(SEM) were employed for selected sub-
sets of the participate samples to yield
information on specific trace elements
and size distribution. The LMUATS
goals were to evaluate methods of
sample collection and analysis, quan-
tify the atmospheric concentrations of
toxic substances in the lower Lake
Michigan area, compare measurements
made over land and over water, differ-
entiate the Chicago urban plume from
regional background, identify catego-
ries of sources for the target pollut-
ants, and estimate deposition to the
lake.
This Project Summary was developed
by EPA's Atmospheric Research and
Exposure Assessment Laboratory, Re-
search Triangle Park, NC, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The presence of persistent toxic sub-
stances within the Great Lakes Basin has
been a matter of interest in both the United
States and Canada for many years. Of
particular concern are those contaminants
that tend to bioaccumulate in the food
chain. These include several of the pesti-
cides, PCBs, and some trace elements
(especially mercury (Hg)). Advisories have
frequently been issued by local health au-
thorities, warning against overconsump-
tion of fish taken from the lakes. In recent
years, much effort has been directed to-
ward reducing or eliminating direct dis-
charges of contaminants to the lakes and
tributaries. In addition to these obvious
sources, however, some studies have sug-
gested that atmospheric transport and
deposition processes may account for a
significant portion of the overall loadings
of toxic substances to the lakes. Section
112(m) of the 1990 Clean Air Act Amend-
ments (CAAAs) specifically requires a pro-
gram to identify and assess the extent of
atmospheric deposition of hazardous air
pollutants to the Great Lakes, as well as
to other large lakes and coastal waters.
-------
EPA's Atmospheric Research and Envi-
ronmental Assessment Laboratory at Re-
search Triangle Park, NC (AREAL/RTP),
in consort with EPA's Region 5, decided
to take advantage of the extensive meteo-
rological database being generated by the
1991 LMOS by conducting a concurrent
air toxics monitoring study in the lower
Lake Michigan area. This project, the
LMUATS, was designed to serve as a
pilot for the atmospheric measurements
portion of the 1994-1995 Lake Michigan
Loadings Study. LMUATS participants in-
cluded AREAL/RTP, the National Oceanic
and Atmospheric Administration's
(NOAA's) Atmospheric Turbulence and
Diffusion Division (ATDD), the University
of Michigan, Illinois Institute of Technol-
ogy, Massachusetts Institute of Technol-
ogy, ManTech Environmental, Battelle,
Southwest Research Institute, and Sunset
Laboratories.
Procedure
Three land-based sites were selected
for monitoring air toxic concentrations in
the lower Lake Michigan Basin. The
LMUATS sampling site locations are
shown in Figure 1. Southwesterly winds
are normally predominant during the sum-
mer months in the upper Midwest. The
sites were located to characterize air toxic
concentrations upwind, within, and down-
wind of the Chicago/Gary urban area. Two
sites (Kankakee, IL and South Haven, Ml)
were collocated with the LMOS program
to maximize the usefulness of the infor-
mation collected. Most of the sampling
equipment, setup, and operator training
for the LMUATS was provided by AREAL7
RTP. Through a cooperative agreement
with EPA, the University of Michigan man-
aged the field sampling program, provided
a research vessel (the R/V Laurentian) for
making measurements over the lake on
selected days, performed the sampling and
analytical work for determining Hg con-
centrations in both the vapor and particu-
late phases, and managed the data
analysis for the entire study.
Daily samples were collected at each
ground site from July 8 through August 9,
1991. The R/V Laurentian was in opera-
tion on July 11 and 12 along the eastern
shore near Grand Haven, Ml, and from
July 23-27 and August 5-8, 1991, at a
position approximately six miles offshore
from the Chicago/Gary waterfront. Samples
were integrated over a 12-hour period,
beginning at 8:00 A.M. CDT. Table 1 sum-
marizes the sampling and analytical tech-
niques employed for each class of
pollutants measured. Because of the rela-
Figure 1. Lake Michigan Urban Air Toxics Study sampling locations.
Table 1. Measurements from the Lake Michigan Urban Air Toxics Study
Sampler
Sample
Samplers Duration
Per Site (hours)
Sampling Media
Analysis Method
PS1-PUF Sampler 2
FPS 1
Annular Denuder/FP 1
DIG HOT 1
VOC Canister System 1
Hg Systems
1 . Au Sand/Filter 1
2. Filter w/INAA 1
3. Filter 1
Micro-Orifice Impactor* 1
12
12
12
12
12
6/12
12/24
12/24
24
PUF/Quartz
Filter
47 mm Quartz
NaCO3/Teflon
37 mm Teflon
6-L Canisters
Au/Quartz
47 mm Teflon
47 mm Quartz
37 mm Teflon
GC/MS
Carbon
1C
XRF/INAA/SEM
GC/MS
CVAFS
INAA
CVAFS
1C
Micro-orifice impactors were only run on the RV Laurentian and at the South Haven site fora limited
number of days.
-------
tively high costs for mass spectrometrical
analysis of semivolatile organic compounds
such as pesticides, PCBs, and PAHs, it
was decided in advance to analyze only a
subset of samples collected for these com-
pounds. The Particulate Sampler-1
samples collected each day were shipped
in cold packs to the appropriate labora-
tory. Filters and traps were combined, de-
sorbed, and placed in cold storage. A
decision regarding which samples to ana-
lyze was made after an examination of
the particulate, trace element, and meteo-
rological data.
Trace element data were obtained for
both fine (< 2.5 \i) and coarse (2.5-10 \L)
particles using a nondestructive X-ray fluo-
rescence (XRF) technique. A subset of
filters was then sent to the Massachusetts
Institute of Technology Nuclear Reactor
Lab for neutron activation analysis to ob-
tain information on Hg and other elements
at very low particulate concentrations. Ad-
ditionally, some filters were examined by
SEM to obtain element-specific size distri-
butions for estimating dry deposition rates.
Fine particle samples were analyzed by
Sunset Labs using combustion flame ion-
ization detection to measure total elemen-
tal and volatilizable carbon content, useful
for source apportionment. Samples for
gaseous Hg were collected at all sites
except Kankakee via amalgamation on
gold-coated sand, following a pre-fired
glass fiber filter. These samples, along
with some filter extracts, were analyzed
for Hg content at the University of Michi-
gan using cold-vapor atomic fluorescence
(CVAF). Annular denuder samplers were
operated for acid and basic aerosol mea-
surements at the South Haven site and
aboard the R/V Laurentian.
Micrometeorological measurements
were made aboard the research vessel to
determine the vertical structure of the at-
mosphere in the layer just above the lake
surface. Flux information was considered
useful for making inferences about likely
deposition rates of toxic substances to the
lake. Rapid-response instruments were
mounted off the vessel's bow to measure
wind direction, wind speed, temperature,
water vapor, carbon dioxide, and ozone.
These measurements were taken at loga-
rithmically spaced elevations between two
and seven meters above the lake surface.
In addition, on five days (July 21-25, 1991)
identical and coordinated measurements
were made aloft aboard a small aircraft
flown at low elevations by NOAA's ATDD.
This information was used, in conjunction
with the LMOS database, to estimate dry
deposition rates.
Results and Discussion
During the course of the month-long
investigation, two periods were encoun-
tered in which the prevailing wind flow
was from the south-southwest and pollut-
ant levels were elevated on a regional
scale. This provided an opportunity to ob-
serve the behavior of the many classes of
compounds as they were advected from
source regions in Illinois (and further south)
across the lake to South Haven. The con-
centrations of particulates and vapor phase
Hg decreased as they were advected from
the urban source region. From the shift in
size distribution, it was evident that the
coarse matter was being depleted by dry
deposition as the aging air mass was ad-
vected from Chicago over the water to the
downwind monitoring site in South Haven.
As a result of both dispersion and deposi-
tion, the concentrations of most com-
pounds decreased rapidly to the regional
or "background" levels within a short dis-
tance from the urban/industrial areas.
Generally, the monitoring site in urban
Chicago (NT) had the highest concentra-
tions of the toxic pollutants and trace ele-
ments measured. The trace element
concentrations in Kankakee, however,
were often comparable to Chicago. This
is in contrast to the other two sites,
over-water and South Haven, where lev-
els of most trace elements were at least a
factor of two less than at NT. Specifically
for Hg, the median concentration of vapor
phase Hg was four times higher at NT
when compared to over-water and South
Haven measurements, while the maximum
concentration was more than 15 times
higher. Particulate Hg levels were also 5
to 15 times higher at NT than at South
Haven or on the R/V Laurentian, suggest-
ing that local sources are primarily re-
sponsible for the Hg levels observed at
the NT site.
During periods of air flow from the north
and northwest, pollutant concentrations
measured at Chicago, South Haven, and
aboard the R/V Laurentian were typically
quite low. Levels of some of the fine frac-
tion metals such as Pb, Fe, Mn, and Zn
measured in Kankakee during these peri-
ods were elevated above the levels ob-
served at NT. Since the NT site in Chicago
is only 1.6 km from the lake, this suggests
an impact due to source(s) between the
two sites (e.g., in the southeast Chicago/
Gary area).
Concentrations of the more reactive
compounds, such as many PAHs, were
uniformly and significantly (order of mag-
nitude) higher at NT than at the other
three monitoring sites. It is interesting to
note that most of the measured PAHs
were found in higher concentrations over
the water than at the South Haven site for
several days and on average. Concentra-
tions of naphthalene, acenaphthylene, and
retene exhibited somewhat uniform con-
centrations among sites, suggesting a
more regional source distribution.
A review of the total PCS measure-
ments during the period for which the pre-
vailing flow was from the southwest
indicates that total PCBs were not trans-
ported from the Chicago urban area down-
wind to South Haven. This implies a strong
concentration gradient of PCBs around
Chicago, with rapid dispersion of the al-
ready low levels of these compounds simi-
lar to the pattern observed for Hg.
However, the low levels of these com-
pounds do not imply that they are unim-
portant with regard to deposition. On the
contrary, the deposition of relatively small
amounts of pollutants such as Hg and
PCBs, which biomagnify in the food chain,
are currently believed to account for a
substantial portion of these toxins enter-
ing the Great Lakes.
The majority of the pesticides/herbicides
quantified during the LMUATS were high-
est in concentration at Kankakee. Notable
exceptions were aldrin and simazine, which
were found in higher concentrations at NT
than at the other three sites, and DDT
and its derivatives, which were highly el-
evated at the South Haven site. The ratio
of DDT to DDE at South Haven (0.3)
strongly suggests that these levels were
due to re-emission of a much earlier DDT
application. Average concentrations for
many currently used pesticides/herbicides
(e.g., atrazine) were two to three times
higher on average at Kankakee than at
NT. Significant concentrations of many pes-
ticides were observed at over-water sites,
both in the eastern portion of the lake (at
the 100 m station off Muskegon) as well
as offshore of Chicago.
The influence of the iron-steel industry
on the composition of the aerosol mea-
sured during the LMUATS was clearly ob-
served. The Fe concentrations in both
fractions of PM10 were elevated at all three
sites and exceeded the contribution ex-
pected from windblown dust. Analysis of
the fine fraction trace element data from
NT using principal component analysis
yielded four dominant source categories:
iron and steel manufacturing, metals pro-
cessing, soil-derived components, and a
regional coal combustion source domi-
nated by sulfur. A secondary Al smelter
located in the St. Louis area may be the
source of several metals, including Al,
measured at relatively high concentrations
at the land-based sites on several occa-
sions.
-------
The chemical mass balance approach
to source apportionment was applied to
the NT measurement data using source
categories based on the EPA database
SPECIATE in conjunction with published
source profiles. For days with predomi-
nant flow from the southwest, this model
was able to explain up to 69% of the
observed coarse mass with significant con-
tributions from crustally derived material,
lime dust, and fugitive steelyard and incin-
erator emissions. Due to the complexity of
the airshed and lack of appropriate source
profiles, the model was not able to effec-
tively explain the fine mass measured at
NT.
To verify the results of statistical source
apportionment, scanning electron micros-
copy was applied to a subset of particu-
late samples collected at NT. This analysis
provides a description of morphology and
elemental composition on an individual
particle basis. The SEM results lend strong
evidence to support many of the suspected
source categories including iron and steel,
coal combustion, incineration, Al produc-
tion, diesel emissions, and resuspended
soil. The complexity of the particulate mat-
ter collected is evident in the photomicro-
graphs generated by the SEM process.
The long-chain Fe spheres, proliferation
of sulfate aerosols, soot conglomerates,
and intricately patterned salts and other
crustal matter illustrate the diverse par-
ticulate mixture abundant in the Chicago
urban atmosphere.
The measurements documented in this
study provide evidence to support the hy-
pothesis that near-shore urban areas can
be significant contributors to atmospheric
levels and, therefore, to deposition of toxic
pollutants to adjacent water bodies. The
1990 CAAA require that the sources and
rates of atmospheric deposition of haz-
ardous air pollutants to water bodies be
investigated and determined. Critical to
this determination is a characterization of
the impact of local urban plumes on the
total toxic burden to the Great Lakes and
other "Great Waters."
The dry deposition fluxes to Lake
Michigan for selected trace metals as-
sociated with both fine and coarse par-
ticles were estimated using a novel
hybrid receptor-deposition modeling ap-
proach. This model included parameters
that take into account the variability in
deposition flux over the lake as a function
of meteorological variables, particle size
distributions, the physics of water waves,
and the type and location of sampling
sites. Significant temporal and spatial varia-
tions in deposition velocities were obtained
for trajectories traversing Lake Michigan
from one day to the next, demonstrating
the unreliability of calculating deposition
flux using deposition velocities assumed
to be constant in time or space over the
entire area of the water body.
The results of the dry deposition model-
ing indicate that Si had the highest depo-
sition flux during the LMUATS (360 tons)
for trace elements measured, followed by
Ca (254 tons), Fe (160 tons), Al (150
tons), K (58.3 tons), S (55 tons), Zn (4
tons), Mn (2.35 tons), Cu (2.2 tons), Cd
(1.07 tons), Pb (1.07 tons), Se (0.93 tons),
Ni (0.8 tons), Cr (0.53 tons), As (0.44
tons), Br (0.38 tons), and total Hg (0.035
tons). The dry deposition flux to Lake
Michigan for specific pollutants contrib-
uted by sources in the Chicago/Gary ur-
ban area is estimated to be two to ten
times greater than that from regional
sources.
Conclusions and
Recommendations
The following conclusions are based on
the measurements made during the
LMUATS and the subsequent analysis of
those and related data:
1. The median concentration of vapor
phase Hg was four times higher at
NT than over water or downwind
(South Haven), while the maximum
concentration was over 15 times
higher. Particulate Hg levels were
also 5 to 15 times higher in Chi-
cago (NT) than at South Haven or
on the research vessel, suggesting
that local sources are primarily re-
sponsible for the Hg levels observed
in Chicago.
2. Median PAH concentrations were
generally 10 times higher at the
urban site (NT) than at the rural
monitoring locations. Some PAH
(e.g., napthalene, retene, acenaph-
thylene) exhibited regional patterns,
indicating long-range transport.
3. PCS levels were about three times
higher at NT than at the other sites
and were generally found to be
higher over the lake than at the
downwind or upwind sites.
4. Most currently used pesticides were
observed at their highest concen-
trations at the background site
(Kankakee), no doubt due to local
agricultural usage patterns. How-
ever, DDT and its derivatives were
found primarily at the Michigan site
in patterns suggesting historical
rather than current usage.
5. Source apportionment models
clearly indicated the influence of
the iron and steel industry on trace
element concentrations, particularly
at the NT site. SEM analysis of a
subset of particulate filters con-
firmed those results.
6. A dry deposition flux model was
developed to use observed con-
taminant concentrations and meteo-
rological data to estimate deposition
by integrating over both time and
lake surface area.
7. Using this hybrid receptor-
deposition model, estimates were
obtained for summer dry deposi-
tion fluxes ranging from 360 tons
Si to 0.035 tons total Hg.
Some recommendations for further
"Great Waters" research developed from
the experience gained in the LMUATS are
as follows:
1. Develop accurate emission inven-
tories for the highest priority pollut-
ants.
2. Obtain better source profiles for
modeling through stack and other
source sampling.
3. Perform research of depositional
processes for use in deterministic
and hybrid models.
4. Characterize large particle contri-
bution to deposition for near-shore
urban areas.
5. Evaluate the importance of
over-water vs. inland vs. shoreline
monitoring locations.
6. Investigate gas-particulate partition-
ing processes for semivolatile com-
pounds.
7. Determine re-emission rates for Hg,
PCBs, and pesticides that have
been discontinued.
-------
Gerald J. Keeler is with the University of Michigan, School of Public Health, Ann
Arbor, Ml 49109-2029.
Gary F. Evans is the EPA Project Officer (see below).
The complete report, entitled Lake Michigan Urban Air Toxics Study," (Order No.
PB95-129102; Cost: $44.50, 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
Atmospheric Research and Exposure Assessment Laboratory
U. S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-94/191
------- |