United States
Environmental Protection
Agency
Atmospheric Sciences Research
Laboratory
Research Triangle Park NC 27711
.*
Research and Development
EPA/600/S3-85/035 June 1985
&EPA Project Summary
Trends in Sulfur Dioxide
Emissions from the Electric
Utility Industry and Ambient
Sulfur Dioxide
Concentrations in the
Northeastern United States,
1975 to 1982
Allison K. Pollack and C. Shepherd Burton
Trends in monthly power plant SO2
emissions and monthly average ambient
SO2 concentrations are determined for
21 northeastern states and the District
of Columbia. Due to the recession of
the late 1970's, power plant emissions
in most of the industrialized states
decreased by up to 30%. Meanwhile,
for more than half of the states, there is
evidence of a downward trend in the
ambient concentrations, even though
many of the monitoring sites were
located in urban areas.
Correlations of the seasonally adjust-
ed emissions and ambient concentra-
tions were calculated at the local, state,
and regional levels. In general, higher
correlations are observed in those states
with higher levels of emissions. In the
six-state region of the Ohio River Valley
the correlation between the seasonally
adjusted emissions and ambient con-
centrations was 0.75.
This Project Summary was developed
by EPA's Atmospheric Sciences Re-
search 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 infor-
mation at back).
Introduction
A key issue in the debate over legis-
lated SO2 emissions reductions is the
extent to which acidic deposition and
precursors of acidic deposition, e.g.,
ambient S02, will be reduced as a result
of reductions in emissions. For example,
will a 50-percent decrease in S02 emis-
sions result in a 50-percent decrease in
ambient S02 and sulfate concentrations
and a 50-percent decrease in acidic
deposition, or only a 25-percent decrease?
Considerable effort is being expended in
sophisticated mathematical model devel-
opment and in the design of field mea-
surement programs to attempt to answer
this and related questions.
Another approach is considered in this
report. As a result of the economic reces-
sion in the late 1970s, actual sulfur diox-
ide emissions were reduced. Data from
the late 1970s and early 1980s, then, can
be used to examine the results of actual
decreases in SO2 emissions. The purpose
of this study is to examine recent trends
in sulfur dioxide emissions and acid
deposition precursors, specifically ambi-
ent S02, and to assess the degree of
correlation between the two. This work is
seen as the first step in a two-step pro-
cess, in which the second step would be
-------
-V
£
to examine the association between
reductions in S02 emissions and/or
ambient S02 and sulfate concentrations
and sulfate deposition.
In this report we address the first step,
reporting on our examination of trends in
(1) sulfur dioxide emissions from electric
power plants, and (2) ambient S02 con-
centrations from 1975 to 1982. The
region of study is the heavily industrial-
ized northeastern United States, extend-
ing to Wisconsin and Illinois on the west
and to Tennessee and North Carolina in
the south. Twenty-one states plus the
District of Columbia (hereafter referred to
as 22 states for simplicity) are included in
the study.
Power Plant Sulfur Dioxide
Emission Trends
The power plant emissions for most
states have a regular yearly pattern, with
a summer peak in July and August and an
even higher winter peak in December and
January. In those states which have high
S02 emissions, such asOhio, Illinois, and
Kentucky, significant decreases can be
seen. In states with relatively few power
plants and low emissions, such as Con-
necticut and Delaware, trends in emis-
sions are difficult to detect apart from the
large seasonal variability.
The power plant emissions for 1975
and 1976 did not change significantly for
any of the high emission states. After
1976 or 1977, however, a general decline
in the emissions was observed for the
District of Columbia, Illinois, Kentucky,
Michigan, New York, Ohio, Pennsylvania,
Tennessee, Virginia, West Virginia, and
Wisconsin. The largest decline in emis-
sions was observed for Tennessee (about
30% from 1977 to 1982). On the other
hand, power plant emissions in Massa-
chusetts increased sharply after 1977.
Ambient Sulfur Dioxide Trends
Trends in monthly mean and average
daily maximum SO2 concentrations were
calculated for each of the 22 states. The
monthly averages were based on aver-
ages across all reporting sites for each
state; because the monitoring sites tend
to be clustered in urban areas, monthly
average values usually reflected concen-
tration levels of those urban monitors
rather than those of background or rural
monitors. Although the absolute levels of
the concentrations within a state may
reflect higher urban concentrations, the
relative levels (i.e., the increases and
decreases observed) may be more repre-
sentative of all areas in the state.
S02 concentrations for the urban-repre-
sentative averages are highest in the win-
ter when (1) the SO2 emissions from low-
elevation, sulfur-containing-fueled heat-
ing sources are highest, (2) the air is
relatively stagnant, and (3) mixing vol-
umes are small; and lowest in the hot
summer months when emissions from
low-elevation sources are less and there
is greater mixing. Sometimes one ob-
serves a secondary "peak" in the summer
season, with an amplitude that is about
10 percent of the winter peak.
The states where downward trends in
monthly average ambient S02 concentra-
tions were detected during 1975-1982
were Delaware, Illinois, Indiana, Ken-
tucky, Michigan, Ohio, Pennsylvania,
Virginia, and Wisconsin. Maryland was
the only state where monthly average
concentrations increased throughout the
period. No trend was apparent in the
remaining states.
Correlations at the State Level
Plots of monthly statewide ambient
S02 mean average daily maximum con-
centrations and power plant emissions
revealed, in general, long-term reductions
in ambient SO2 concentrations in addi-
tion to long-term reductions in emissions;
however, no clear pattern emerged with
respect to short-term correlations be-
tween changes in emissions and changes
in ambient S02. Short-term correlations
are not clearly apparent because of the
highly seasonal nature of both emissions
and ambient concentrations: ambient SO2
concentrations peak during the winter,
whereas emission levels have a winter
peak as well as a summer peak.
The correlations of interest are between
the seasonally adjusted emissions and
the seasonally adjusted S02 concentra-
tions. If the differences between actual
and typical seasonal emissions are corre-
lated with the differences between actual
and typical seasonal S02 concentrations,
then short-term changes in ambient SO2
levels are related to short-term changes
in emissions.
These correlations are highest in those
states with greater power plant SO2
emissions. The degree of correlation
depends to some extent on the number of
S02 monitors and the amount of data at
each of the monitors; the more monitor-
ing data there are, the less variability
there is in average monthly SO2 concen-
trations and the more likely it is that
actual correlations between emissions
and ambient S02 concentrations will be
seen. In addition, the degree of the corre-
lation depends on the locations of the SO2
monitoring stations relative to the loca-
tions of the power plants with sizeable
S02 emissions.
Correlations at the Local Level
Relationships between individual pow-
er plant emissions and monitored SO2
concentrations were examined for a few
selected sites. Such relationships, how-
ever, are inherently difficult to analyze
because of missing data at most S02
monitoring stations. Very few stations
were in existence during the entire 8-
year period under study, and even when
monitors are operating they rarely record
measurements for all of the hours in a
given year. From the set of monitors with
at least 4 years of at least 50 percent of
the total possible hours each year, we
selected three with power plants nearby
for further analysis; two of the monitor
pairs are in New York near the Pennsyl-
vania border, and the third is in eastern
Virginia.
The correlations between emissions
and SO2 concentrations in these local
sites can be summarized as follows:
• Correlations are highest for point-
source monitors near large power
plants;
• Correlations between monthly emis-
sions from power plants and monthly
average daily maximum SO2 concen-
trations are somewhat higher than
correlations between emissions and
mean S02 concentrations;
• Correlations between power plant
emissions and ambient SO2 concen-
trations are improved when the month-
ly data are aggregated to yearly aver-
ages; and
• Correlations between power plant
emissions and ambient SO2 concen-
trations are higher when just the
subset of summer months is consid-
ered. This is a period in which emis-
sions are high and mixing of emissions
from elevated sources is greatest.
Correlations at the Regional
Level
Regional power plant S02 emissions
and ambient S02 concentrations de-
creased substantially after 1976 along
the Ohio River Valley states (Illinois, Indi-
ana, Ohio, Pennsylvania, West Virginia,
and Kentucky). From 1975 to 1982, total
six-state SO2 emissions from power
plants decreased 22 percent, average
ambient SO2 concentrations decreased
-------
33 percent, and average daily maximum
S02 concentrations decreased 32 per-
cent, which indicates that emission reduc-
tions from sources other than power
plants have occurred.
Seasonally adjusted statewide SOa
emissions and ambient concentrations
were compared for the Ohio River Valley
states. There was a correlation of 0.749
between changes in emissions from the
seasonal pattern and changes in monthly
average S02 from seasonal patterns; for
monthly average daily maximum S02
concentrations, the correlation is 0.766.
Simple regression analyses reveal that
an emissions decrease of 100,000 tons of
S02 from power plants in the region in a
given month from what would normally
be expected for that month of the year is
associated with a decrease of 0.031 ppb
in monthly average S02(from what would
normally be expected for monthly aver-
age SO2for that month) and a decrease of
0.084 ppb in monthly average daily max-
imum S02(from what would normally be
expected for the month).
Conclusions
Substantial decreases in both S02
emissions and ambient concentrations
occurred in the northeastern quadrant of
the United States during the 1975-1982
study period. Annual power plant emis-
sions from the six-state Ohio River Valley
region decreased 22 percent from 1975
to 1982, while annual average daily max-
imum ambient concentrations decreased
32 percent during the same period. In this
region the correlation between season-
ally adjusted monthly power plant emis-
sions and seasonally adjusted monthly
average ambient concentrations was
0.75. Correlations at the state and local
levels were lower.
A. K. PollackandC. S. Burton are with Systems Applications. Inc., SanRafael. CA
94903.
Terry L. Clark is the EPA Project Officer (see below).
The complete report, entitled "Trends in Sulfur Dioxide Emissions from the
Electric Utility Industry and Ambient Sulfur Dioxide Concentrations in the
Northeastern United States. 1975 to 1982," (Order No. PB 85-200 244/AS;
Cost: $16.00. 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 Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
U.S. GOVERNMENT PRINTING OFFICE: 1985-559-016/27077
-------
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penalty for Private Use $300
OCOC329 PS
U S ENVIR PROTECTION AGENCY
REGION 5 LIBRARY
230 S DEARBORN STREET
CHICAGO IL 60604
l.ll,.11....II..II.,,II.,,!.,!.I
------- |