ATMOSPHERIC EMISSIONS OF TRACE METALS IN THE GREAT LAKES
PIRRONE, N.(1) and
NRIAGU, J.O.(2)
(1) CNR-Institute for Atmospheric Pollution, c/o: UNICAL, 87036 Rende, Italy
(2) Dept. Environmental Health Sciences, SPH-I, University of Michigan, Ann
Arbor, MI 48109, USA
ABSTRACT
State-by-state annual emissions of anthropogenic trace elements to the
atmosphere are estimated for the Great Lakes region and compared with ambient
concentrations measured in major urban areas including Chicago, Detroit,
Cleveland and Toronto from 1981 to 1993. Regionwide, industries in the province
of Ontario are implicated as the leading sources of Cd, Pb and Cu released to
the atmosphere in the Great Lakes basin, accounting for about 50%, 38% and 28%
of the regional total, respectively, whereas Indiana, Ohio and Pennsylvania
emit nearly 50% of the total Ni, Cr, Mn and As emissions. Regional Hg emissions
vary from 10% in the province of Ontario to 17% in the state of New York. On regional basis, the total anthropogenic
emissions peaked in the 1988 at about 1040
t yr-1 for Ni, 280 t yr-1 for Cr, 900 t yr-1
for Cu, 1170 t yr-1 for Mn, 550 t yr-1 for As and 118 t
yr-1 for Cd. After 1988, the
Ni emissions decreased, whereas for Cr, Cu, Mn, As and Cd the emissions did not
show significant changes. Mercury
emissions increased up to 1989 at a rate of about 4 % yr-1 and have
since remained nearly constant. By
contrast, regional Pb emissions decreased steadily at a rate of 6.4 % yr-1
which reflects the phase down in Pb content in gasoline in Canada and United
States during the 1980`s.
Key Words: atmosphere, emission, trace
element, anthropogenic source, Great Lakes, emission factor
INTRODUCTION
Emission
inventories of toxic substances released from natural and anthropogenic sources
are needed in mass balance models, transport and deposition models, for
relating mesoscale variations in aerosol composition with regional and global
circulation patterns, and in assessing long-term ecological and health impacts
on different environmental ecosystems as well as on biota (Nriagu and Pacyna,
1988; Voldner and Smith, 1989; US-EPA, 1994; Pirrone et al., 1996; Nriagu and Pirrone, 1998; Mamane and Pirrone, 1998;
Pirrone et al., 1999; Pirrone et al., 2000). Atmospheric transport and deposition processes represent the
major pathways in the transfer and redistribution of a wide array of hazardous
air pollutants (HAPs) (i.e., trace metals, NOx, SOx, O3, PAHs,
pesticides, PCBs, VOCs) in the environment (Voldner and Smith, 1989; Keeler et al., 1995; Pirrone et al., 1995). Temporal variations in
ambient concentrations and deposition fluxes of trace elements on urban scales
as well as on regional and global scales are of considerable environmental
interest and are receiving intensive scrutiny.
Pirrone et al. (1996; 1996-a) reported an increase in
ambient concentrations of about 3.6 % yr-1 for Zn, 5.7 % yr-1
for Ni, 1 % yr-1 for Cr, 0.6 % yr-1 for Cd and 16 % yr-1
for Hg, and a decrease of about 9.8 % yr-1 for Pb in the urban area
of Detroit, Michigan during the 1982-1992.
A 2 % annual increase in Hg deposition rates was reported by Swain et al. (1992) for remote lakes in
Wisconsin and Minnesota. In comparing
historical trends (1800-1990) of atmospheric Hg deposition with Hg accumulation
in Great Lakes sediments, Pirrone et al.
(1998) concluded that atmospheric deposition has been the major diffuse source
of Hg entering surface waters in the region.
Therefore, emission inventories coupled with historical records of
ambient concentrations or/and accumulation rates in lake’s sediments are
necessary to improve our understanding of the biogeochemical cycle of major
HAPs in the environment. This paper is aimed at assessing annual
emissions of Pb, Ni, Cr, Cu, Mn, As, Cd and Hg to the atmosphere in the Great
Lakes region from 1981 to 1993 and compare atmospheric emissions with ambient
concentrations measured at residential, commercial and industrial sites of
major urban areas of the Great Lakes.
METHODOLOGY
Emissions
of trace elements to the atmosphere from industrial processes depends upon (a)
the concentration of trace elements in the raw materials; (b) processing
technology employed; and (c) type and efficiency of control equipment (Nriagu
and Pacyna, 1988; Pirrone et al.,
1996; Pirrone et al., 1998). In the absence
of valid measured data, emission factors are used to estimate annual emissions
on regional and global scales, and are employed in setting national and
international environmental policies and control regulations. Table I shows selected emission factors (and
the reported range) for major industrial processes used to derive annual
emissions of trace elements to the atmosphere in the Great Lakes region. The values reported in Table I are based on
recent studies carried out in the United States, Canada and Europe (Nriagu and
Pacyna, 1988; Benjey and Coventry, 1992; Wilber, et al., 1992; US-EPA, 1994; Pirrone et al., 1996; Skeaff and Dubreuil, 1997; Pirrone et al., 1998; 1998; Pirrone et al., 1999). In this report trends of the emission inventory are related to
temporal variations of emission factors (when available) and to trends of (a)
fossil fuels consumption for energy production and industrial/commercial uses,
(b) amount of urban and industrial wastes disposed off through incineration
facilities, and (c) production of goods from a variety of industrial
processes. The upper range of emission
factors reported in Table I applies to the beginning of 1980s when control
measures were not substantial (Nriagu and Pacyna (1988); Swaine, 1990; EIA,
1993; Wilber, et al., 1992), whereas
the lower range reflects the effect of improved control technologies (e.g.,
electrostatic precipitators, multicyclone, scrubber) and coal cleaning (US-EPA,
1994; Pirrone et al., 1996; Pirrone et al., 1997) implemented in recent years
in the United States and Canada for major industrial sources and were derived
from a number of peer-reviewed publications (i.e., US-EPA, 1994; Chu and
Porcella, 1995; Pirrone et al., 1996;
Skeaff and Dubreuil, 1997; Pirrone et al.,
1998; 1999). The lower range of
emission factors used for primary and secondary non-ferrous smelters is that
reported by Skeaff and Dubreuil (1997) for Canadian smelters for the 1993-base
year.
RESULTS AND DISCUSSION
Annual anthropogenic emissions of Pb, Ni, Cr, Cu, Mn, As, Cd and Hg to
the atmosphere in the Great Lakes region were estimated for the period of 1981
to 1993. Regionwide, the steady
increase in emissions peaked in the 1988 at about 4430 t yr-1 for
Pb, 2510 t yr-1 for Cr, 1630 t yr-1 for Cu, 1030 t yr-1
for Mn, and 150 t yr-1 for Cd.
The rate of increase up to 1988 was about 3.2 % yr-1 for Ni,
2 % yr-1 for Cr, 1.9 % yr-1 for Cu, 2.7 % yr-1 for Mn and 5.2 % yr-1
for Cd (assuming the 1981 as the base year).
Arsenic did not show any particular emission patterns during the
1981-1988. After 1988, the emissions
decreased steadily at an annual rate of about 1.8 % for Ni, 1.4 % for As, 0.5 %
for Cu, 0.4 % for Cr and 0.4 % for Mn, whereas Cd emissions did not show
significant changes. Mercury emissions
peaked in the 1989 at about 110 t yr-1 (nearly 4 % yr-1)
and have since decreased at a rate of 0.7 % yr-1. Similarly, Hg emissions in North America
have been reported by Pirrone et al.
(1996) to increase at a rate of about 4.8 % yr-1 up to 1989 and have
remained nearly constant since then, although different patterns in emissions
and ambient levels have been observed at local and urban scales (Pirrone et al. 1996). By contrast, Pb emissions decreased steadily at a rate of 6.4 %
yr-1, which is in good agreement with the phase-down in Pb content
of gasoline sold in the United States and Canada during the 1980`s.
Our
emission estimates are in general agreement with emission inventories reported
by Voldner and Smith (1989), Wilber et al.
(1992) and Benjey and Coventry, (1992) for the 1980’s. Emissions of trace elements to the
atmosphere in the Great Lakes have been reported to be (1985 estimates) about
8800 t yr-1 for Pb, 800 t yr-1 for As, 140 t yr-1
for Cd, and 75 t yr-1 for Hg (Voldner and Smith, 1989; Benjey and
Coventry, 1992) compared to 8877 t yr-1 for Pb, 517 t yr-1
for As, 251 t yr-1 for Cd and 89 t yr-1 for Hg reported
in this study.
The
coal combustion in electric power plants and industrial utilities is implicated
as the leading source of Cr (~ 52%), Cu (~ 48%) and As (~ 64%) in the Great
Lakes region, whereas incineration of municipal and medical solid wastes as
well as sewage sludge represent the dominant anthropogenic source of
atmospheric Hg and accounts for about 60% of the regional total. Iron-steel manufacturing is the dominant
source of Ni (~ 65%) and Mn (~ 50%), whereas the primary and secondary
non-ferrous metal smelters are important sources of Cd (~ 58%), Pb (~ 35%), Cu
(~ 22%) and As (~ 15%) released to the atmosphere. The analysis of state-by-state emission patterns by source
category shows a number of interesting temporal differences. Lead emissions from fossil fuels (coal +
oil) combustion decreased at an annual rate in the range of 1.4-2.7 % in
Michigan, Ohio, Pennsylvania, New York and Ontario. By contrast, a steady increase (0.4 - 1 % yr-1) in Pb
emissions from this source category occurred in Minnesota, Wisconsin, Illinois
and Indiana due to the increase in coal and oil combustion in electric
utilities and industrial plants.
Increasing trends in emissions were found for most of trace elements in
Minnesota, Wisconsin and Indiana, whereas all other states of the Great Lakes
region were characterised by declining emissions.
Figure
1 shows the fractions of the trace elements emission on state-by-state basis
for the 1993. Emissions from the
incineration of solid wastes and sewage sludge increased steadily in all the
states due to the increase in waste generation rates and fractions of wastes
disposed off through this particular process.
Annual increases in emissions from waste and sewage sludge incineration
in the region (assuming the 1981 as the
base year) were in the range of 9-18% for Pb, 0.6-11% for Ni, 1-13% for Cr,
1.7-11 for Cu, 3-17% for Mn, 3.6-11% for As, 4.2-12.5 for Cd and 3.6-10% for
Hg. Similarly, a substantial increase
(4-7 % yr-1) in emissions of trace elements from iron-steel
manufacturing plants occurred in major producing states of the region including
Illinois, Indiana, Michigan, Ohio and Pennsylvania, though improvements in
processing techniques and emission control capability have been substantial
(US-Bureau of Mines, 1994; US-EPA, 1994).
By contrast, emissions in Ontario from this particular process decreased
at a rate of 2.4-2.8 % yr-1.
Emissions of trace elements from non-ferrous metal production increased
at a rate of 1-3 % yr-1 in Illinois, Pennsylvania and Ontario. Variations up to 8 % yr-1 in
emissions from cement manufacturing plants occurred in major producing states
including Illinois, Indiana, Michigan and Pennsylvania, whereas in Ontario only
Pb (~ 1.5 % yr-1) and As (~ 2.5 % yr-1) emissions showed
significant changes during the last decade.
One of the objectives of
this report was to evaluate possible correlation between ambient concentrations
measured in major urban areas of the Great Lakes region and emissions of trace
elements to the atmosphere at state and regional scales. Univariate and multivariate statistical
analysis were used to seek differences between sets of ambient concentrations
measured within the urban areas, and the multiple regression was used to
formulate source functions between emissions (dependent variable) and ambient
concentrations (independent variables) measured in residential, commercial and
industrial areas. In Figure 2 trends of
statewide emissions and ambient concentrations are compared for atmospheric
lead measured from 1981 to 1993 in major urban areas of the Great Lakes
including Detroit in Michigan, Chicago in Illinois, Cleveland in Ohio and
Toronto in Ontario. The regionwide fall of Pb emissions is in good agreement
with the decrease in Pb concentrations observed in urban areas with an r2
(emissions vs. ambient concentrations) in the range of 82 to 95%. The sharp decrease of Pb levels in urban
areas was mostly due to the reduction of the Pb content in gasoline (from 0.28
g L-1 in the 1982 to 0.026 g L-1 in the 1989) and to an
increase of the ratio unleaded/leaded gasoline consumption in the United States
and Canada since 1981
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