United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Jriangle Park NC 27711
Research and Development
EPA/600/S8-89/042 Dec. 1989
x>EPA Project Summary
Assessment of National and
Regional Acid Deposition
Precursor Emission Trends
James H. Wilson, Jr., Edward H. Pechan, and Kristin Graves
The report that this summary de-
scribes was prepared as part of the
U.S. Environmental Protection Agen-
cy's (EPA's) effort to summarize cur-
rent knowledge on acid trends In
emissions of pollutants considered to
be acid deposition precursors, pri-
marily sulfur oxides (SOX), nitrogen
oxides (NOX), and volatile organize
compounds (VOCs). Special empha-
sis was placed on recent trends
(1980-1985) and on new Information
learned by researchers since 1983,
although comparisons were made
with emission trends from 1940 to
1980 for perspective.
From 1980 to 1985, SOX emissions
showed a net decrease of almost
11%, VOC emissions decreased 7%,
and the change In NOX emissions
was insignificant compared to poten-
tial uncertainties In the analysis
methods. Historically, emissions in-
creased from 1940 to the mid-1970s
as fuel use and Gross National Prod-
uct (GNP) grew. The late 1970s and
early 1980s was the "emissions con-
trol era" when programs enacted un-
der the Clean Air Act produced a
downward emission trend for SOX
and VOC while the economy was still
growing. Since 1980, the relation-
ships between emissions and the
economy, fuel use, and regulations
have become more complex so that
predictions of how economics growth
and control regulations will combine
to affect emissions in future years
are difficult
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Re-
search Triangle Park, NC, to announce
key findings of the research project
that is fully documented In a separate
report of tne same title (see Project
Report ordering information at back).
Introduction
The purpose of this report is to
examine trends in acid deposition pre-
cursor emissions from 1980 through
1985. Emission trends in the 1980s have
important implications for future EPA pol-
icy as potential control efforts need to
take into account how emissions are
changing by source emitting sector and
region.
Emission trends data have been
published for the 1940-1980 time period
by the National Acid Precipitation Asses-
sment Program (NAPAP). More recent
emission trends data are necessary in
order to assess the impact of emission
controls, the economy, and regulations
on emissions. Additionally, data on Cana-
dian emission trends are important since
acid deposition is an international issue
and U.S. source emissions may impact
Canadian receptors and vice versa.
EPA's emissions estimation method
uses national level fuel combustion or
production data, emission factors, and
average levels of pollution control. This
"top-down" method is used to estimate
national emissions in this report. Regional
emissions are estimated using state or
regional activity data.
Scope of Analysis
Annual emissions of SOX, NOX, and
VOC are estimated for the years 1980-
1985. The emissions estimates are com-
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pared to trends in GNP, emissions re-
lease height, and population. Emissions
are estimated by source category (elec-
tric utilities, industrial activities, transpor-
tation, and other), and by Federal admini-
strative region. Canadian emissions from
1970 to 1984 are presented at the nation-
al and source category (fuel combus-
tion/stationary sources, industrial proces-
ses, transportation, and other) levels. U.S.
emissions data from 1940 to 1980 are
presented to provide an historical per-
spective. Emphasis is placed on new in-
formation made available since 1983 by
acid deposition researchers.
Results
U.S. Emissions Trends from 1940
to 1985
Emissions trends since 1940 break
down into three periods. The 1940 to
mid-1970s period was one of emissions
growth during which, generally, emis-
sions increased proportionately with fuel
use and GNP. The latter half of the 1970s
and the early 1980s was the "emissions
control era" when programs enacted
under the Clean Air Act produced a
downward trend for all pollutants except
NOX while the economy and fuel
consumption continued to grow. After
1983, the relationships between emis-
sions and the economy, fuel use, and
regulations became more complex.
The main reason for this added com-
plexity is that many emission reductions
were achieved in the 1970s and early
1980s, and few new programs have been
instituted since then to go beyond those
control levels. The operation and control
of emissions sources which are not regu-
lated by New Source Performance
Standards have a significant effect on
emission trends. Economic factors such
as declining commodity prices and for-
eign competition have reduced emissions
from a number of mineral production and
heavy manufacturing sectors, most
notably copper smelters and iron and
steel mills.
U.S. Regional Emission Trends
from 1980 to 1985
Regional emission patterns often follow
national trends. Eastern regions generally
reduced their SOX emissions at the same
rate as the nation, while western regions,
especially one in which a copper smelter
shut down, experienced larger SOX re-
ductions.
Regional NO* emission trends were
generally downward in the eastern U.S.
and either flat or upward in the west.
Control regulations for NOX are not as
prevalent as they are for other pollutants,
so, except for mobile sources, NOX emis-
sions track almost directly with fuel use.
Regional highway vehicle emission
trends were similar to those observed
nationally: regions with the highest VMT
growth showed the least decline in emis-
sions.
Regional VOC trends tracked national
trends; this lack of regional variation re-
sults from both the absence of dominant
source types and the uncertainty in es-
timating VOC emissions.
Canadian Emission Trends from
1970 to 1984
Easter Canadian SOX emissions de-
creased 44% between 1970 and 1984;
U.S. emissions deceased 24% during this
time period. Eastern Canadian emissions
of NOX, which were 8% of U.S. levels in
1980, increased by 29% between 1970
and 1984, with most of this increase
occurring by 1974. U.S. NOX emissions
increased by 9% from 1970 to 1984. This
information provides a useful historical
perspective between trends of U.S. and
Canadian emissions which could
contribute to transboundary transport of
acidic air pollution.
U.S. Utility SOX Emission Trends
Emissions from coal-fired utility boilers
decreased by 4% from 1980 to 1985.
Much of this reduction was achieved
between 1980 and 1982. Although utility
SOX emissions have declined, an in-
crease in the use of higher sulfur coal or
uncontrolled utility boilers could rapidly
reverse this trend.
The Influence of Stack Height
on the Transport of Emissions
Although emission trends analysis indi-
cates an historic decrease in SOX
emissions, this decrease may be coun-
terbalanced by an increase in the amount
of SO* emitted through tall stacks at
higher elevations and thus more directly
available for long-range transport. Stacl
height, velocity, and temperature increas
es in recent years have been made large
ly to reduce peak concentrations nea
major emission sources to meet ambien
air quality standards without controllini
the quantity of SOX emitted.
U.S. NOX Emission Trends from
1980 to 1985
There is no demonstrable trend in na
tional NOX emissions between 1980 am
1985. However, recent estimates of high
way vehicle NOX emissions indicate
possible increase in these emissions dur
ing 1986 and 1987. This is a change fror
pre-1983 projections that national NO
emissions would decrease as highwa
vehicle emissions decreased. It wa
thought that transportation sector de
creases, the result of increasingly strir
gent NOX emission standards, woul
more than offset any NOX emission ir
creases from utility and industrial sectc
fuel combustion.
U.S. VOC Emission Trends from
1980 to 1985
VOC emissions declined only aboi
half as much as earlier projections for thi
time period indicated. The U.S. EPA e$
timates of VOC emissions prior to 198
appear to have overestimated the reduc
tion in emissions that would be achieve
in response to control programs. This i
due to more rapid than expected vehicl
miles traveled (VMT) growth, increase
popularity of less well controlled new v<
hides, and slower than expected vehicl
turnover. VOC estimates are more unce
tain than those for SOX or NOX.
Emissions in the Near Future
Preliminary fuel consumption data fi
1986 and the current relationship bi
tween coal, oil, and gas prices indica
that emissions of SOX, NOX, and VOC ai
not expected to vary significantly froi
1985 levels during 1986 and 1987, t
though SOX emissions may decrea;
slightly. The flat trajectory of emissic
trends indicates that, without addition
control initiatives, future (1990) emissioi
of all three pollutants will be higher thi
they are now if fuel use and VMT i
crease.
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James H. Wilson, Jr., Edward H. Pechan, and Kristin Graves are with E. H. Pechan
and Associates, Inc., Springfield, VA 22151.
J. David Motley is the EPA Protect Officer (see below).
The complete report, entitled "Assessment of National and Regional Acid Depo-
sition Precursor Emission Trends," (Order No. PB 89-180 483/AS; Cost: $21.95,
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:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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