United States Atmospheric Research and

Environmental Protection Exposure Assessment Laboratory

Agency Research Triangle Park, NC 27711

Research and Development EPA/600/SR-94/191 November 1994

E AP

Lake Michigan Urban Air Toxics

Study

Gerald J. Keeler

Project Summary

During the summer of 1991, an air

toxics monitoring program was conducted in the lower Lake Michigan area.

This study, designated the Lake Michigan Urban Air Toxics Study (LMUATS),

was designed to take advantage of the

intensive meteorological database being generated concurrently by the Lake

Michigan Ozone Study (LMOS). Integrated 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 measure 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 hydrocarbons (PAHs), volatile organic compounds (VOCs), particle mass, and

trace elements.

In addition, Nuclear Activation Analysis and Scanning Electron Microscopy

(SEM) were employed for selected subsets of the particulate samples to yield

information on specific trace elements

and size distribution. The LMUATS

goals were to evaluate methods of

sample collection and analysis, quantify the atmospheric concentrations of

toxic substances in the lower Lake

Michigan area, compare measurements

made over land and over water, differentiate the Chicago urban plume from

regional background, identify categories of sources for the target pollutants, and estimate deposition to the

lake.

This Project Summary was developed

by EPA’s Atmospheric Research and

Exposure Assessment Laboratory, Research 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 substances 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 pesticides, PCBs, and some trace elements

(especially mercury (Hg)). Advisories have

frequently been issued by local health authorities, warning against overconsumption of fish taken from the lakes. In recent

years, much effort has been directed toward reducing or eliminating direct discharges of contaminants to the lakes and

tributaries. In addition to these obvious

sources, however, some studies have suggested 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 Amendments (CAAAs) specifically requires a program 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.
2

EPA’s Atmospheric Research and Environmental Assessment Laboratory at Research Triangle Park, NC (AREAL/RTP),

in consort with EPA’s Region 5, decided

to take advantage of the extensive meteorological 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 included AREAL/RTP, the National Oceanic

and Atmospheric Administration’s

(NOAA’s) Atmospheric Turbulence and

Diffusion Division (ATDD), the University

of Michigan, Illinois Institute of Technology, Massachusetts Institute of Technology, 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 summer months in the upper Midwest. The

sites were located to characterize air toxic

concentrations upwind, within, and downwind of the Chicago/Gary urban area. Two

sites (Kankakee, IL and South Haven, MI)

were collocated with the LMOS program

to maximize the usefulness of the information collected. Most of the sampling

equipment, setup, and operator training

for the LMUATS was provided by AREAL/

RTP. Through a cooperative agreement

with EPA, the University of Michigan managed 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 concentrations in both the vapor and particulate 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 operation on July 11 and 12 along the eastern

shore near Grand Haven, MI, 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 summarizes the sampling and analytical techniques employed for each class of

pollutants measured. Because of the rela0 20 40 60 80 100

Kilometer

South Haven

R/V

Laurentian

Chicago

Kankakee

N

Figure 1. Lake Michigan Urban Air Toxics Study sampling locations.

Kilometers

Table 1. Measurements from the Lake Michigan Urban Air Toxics Study

Sample

Samplers Duration

 Sampler Per Site (hours) Sampling Media Analysis Method

PS1-PUF Sampler 2 12 PUF/Quartz GC/MS

FPS 1 12 Filter Carbon

Annular Denuder/FP 1 12 47 mm Quartz IC

DICHOT 1 12 NaCO3 /Teflon XRF/INAA/SEM

VOC Canister System 1 12 37 mm Teflon GC/MS

Hg Systems 6-L Canisters

1. Au Sand/Filter 1 6/12 CVAFS

2. Filter w/INAA 1 12/24 Au/Quartz INAA

3. Filter 1 12/24 47 mm Teflon CVAFS

Micro-Orifice Impactor* 1 24 47 mm Quartz IC

37 mm Teflon

* Micro-orifice impactors were only run on the RV Laurentian and at the South Haven site for a limited

number of days.
3

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 compounds. The Particulate Sampler-1

samples collected each day were shipped

in cold packs to the appropriate laboratory. Filters and traps were combined, desorbed, and placed in cold storage. A

decision regarding which samples to analyze was made after an examination of

the particulate, trace element, and meteorological data.

Trace element data were obtained for

both fine (< 2.5 μ) and coarse (2.5-10 μ)

particles using a nondestructive X-ray fluorescence (XRF) technique. A subset of

filters was then sent to the Massachusetts

Institute of Technology Nuclear Reactor

Lab for neutron activation analysis to obtain information on Hg and other elements

at very low particulate concentrations. Additionally, some filters were examined by

SEM to obtain element-specific size distributions for estimating dry deposition rates.

Fine particle samples were analyzed by

Sunset Labs using combustion flame ionization detection to measure total elemental 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 Michigan using cold-vapor atomic fluorescence

(CVAF). Annular denuder samplers were

operated for acid and basic aerosol measurements 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 atmosphere 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 logarithmically 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 encountered in which the prevailing wind flow

was from the south-southwest and pollutant levels were elevated on a regional

scale. This provided an opportunity to observe 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 concentrations 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 advected from Chicago over the water to the

downwind monitoring site in South Haven.

As a result of both dispersion and deposition, the concentrations of most compounds decreased rapidly to the regional

or “background” levels within a short distance from the urban/industrial areas.

Generally, the monitoring site in urban

Chicago (IIT) had the highest concentrations of the toxic pollutants and trace elements 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 levels of most trace elements were at least a

factor of two less than at IIT. Specifically

for Hg, the median concentration of vapor

phase Hg was four times higher at IIT

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 IIT than at South

Haven or on the R/V Laurentian, suggesting that local sources are primarily responsible for the Hg levels observed at

the IIT 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 fraction metals such as Pb, Fe, Mn, and Zn

measured in Kankakee during these periods were elevated above the levels observed at IIT. Since the IIT 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 magnitude) higher at IIT 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. Concentrations of naphthalene, acenaphthylene, and

retene exhibited somewhat uniform concentrations among sites, suggesting a

more regional source distribution.

A review of the total PCB measurements during the period for which the prevailing flow was from the southwest

indicates that total PCBs were not transported from the Chicago urban area downwind to South Haven. This implies a strong

concentration gradient of PCBs around

Chicago, with rapid dispersion of the already low levels of these compounds similar to the pattern observed for Hg.

However, the low levels of these compounds do not imply that they are unimportant 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 entering the Great Lakes.

The majority of the pesticides/herbicides

quantified during the LMUATS were highest in concentration at Kankakee. Notable

exceptions were aldrin and simazine, which

were found in higher concentrations at IIT

than at the other three sites, and DDT

and its derivatives, which were highly elevated 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

IIT. Significant concentrations of many pesticides 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 measured during the LMUATS was clearly observed. The Fe concentrations in both

fractions of PM10 were elevated at all three

sites and exceeded the contribution expected from windblown dust. Analysis of

the fine fraction trace element data from

IIT using principal component analysis

yielded four dominant source categories:

iron and steel manufacturing, metals processing, soil-derived components, and a

regional coal combustion source dominated 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 occasions.
4

The chemical mass balance approach

to source apportionment was applied to

the IIT measurement data using source

categories based on the EPA database

SPECIATE in conjunction with published

source profiles. For days with predominant flow from the southwest, this model

was able to explain up to 69% of the

observed coarse mass with significant contributions from crustally derived material,

lime dust, and fugitive steelyard and incinerator emissions. Due to the complexity of

the airshed and lack of appropriate source

profiles, the model was not able to effectively explain the fine mass measured at

IIT.

To verify the results of statistical source

apportionment, scanning electron microscopy was applied to a subset of particulate samples collected at IIT. 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 production, diesel emissions, and resuspended

soil. The complexity of the particulate matter collected is evident in the photomicrographs 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 particulate mixture abundant in the Chicago

urban atmosphere.

The measurements documented in this

study provide evidence to support the hypothesis 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 hazardous 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 associated with both fine and coarse particles were estimated using a novel

hybrid receptor-deposition modeling approach. 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 variations 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 modeling indicate that Si had the highest deposition 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 contributed by sources in the Chicago/Gary urban 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

IIT 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 Chicago (IIT) than at South Haven or

on the research vessel, suggesting

that local sources are primarily responsible for the Hg levels observed

in Chicago.

2. Median PAH concentrations were

generally 10 times higher at the

urban site (IIT) than at the rural

monitoring locations. Some PAH

(e.g., napthalene, retene, acenaphthylene) exhibited regional patterns,

indicating long-range transport.

3. PCB levels were about three times

higher at IIT 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 concentrations at the background site

(Kankakee), no doubt due to local

agricultural usage patterns. However, 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 IIT site. SEM analysis of a

subset of particulate filters confirmed those results.

6. A dry deposition flux model was

developed to use observed contaminant concentrations and meteorological data to estimate deposition

by integrating over both time and

lake surface area.

7. Using this hybrid receptordeposition model, estimates were

obtained for summer dry deposition 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 inventories for the highest priority pollutants.

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 contribution to deposition for near-shore

urban areas.

5. Evaluate the importance of

over-water vs. inland vs. shoreline

monitoring locations.

6. Investigate gas-particulate partitioning processes for semivolatile compounds.

7. Determine re-emission rates for Hg,

PCBs, and pesticides that have

been discontinued.
5

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/SR-94/191

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

Gerald J. Keeler is with the University of Michigan, School of Public Health, Ann

Arbor, MI 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