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OCR for page 87
4 Empirical Observations and
Sou rce- Receptor Re~ati onsh i ps
The analysis of data taken in the field complements the
development of theoretical models as a means for
understanding both the phenomenon of acid deposition and
the responses of the atmospheric system to alternative
emission-control strategies. Field measurements not only
reveal insights into the nature of the atmospheric
processes involved in the deposition of acid-forming
materials but also may hold the greater promise of
providing direct, unequivocal evidence from which
responses to mitigating strategies might be assessed.
Data from which the spatial and temporal distributions of
SO2 and NOx over large regions of North America might
be derived have not been available until recently.
Similarly, reliable sampling of the chemistry of precipi-
tation in North America is a recent development. Even
so, sampling of ambient pollutants in the atmosphere and
sampling of those in precipitation generally have not
been simultaneous. There are no direct measurements of
regional dry deposition for gases or particles. [For a
description of the monitoring systems in North America
and data interpretation, see U.S./Canada work Group #2
(1982).]
Although data are relatively sparse in North America,
those that are available tell us much about the phenome-
non. A more extensive data base exists for northern
Europe, where atmospheric SO2 and sulfate in
precipitation have been monitored systematically for
several decades. Much of our understanding of acid
deposition has come from analysis of the European
experience and the transfer to and replication of those
data on this continent. That being so, differences in
patterns of emissions, climatic factors, ground cover,
and influences of marine air between Europe and North
87
OCR for page 88
88
America require that our understanding be tested against
North American data.
In this chapter we review the existing data for North
America and use the data to assess the extent to which
the relationships between emissions and deposition can be
inferred from observations. The limitations of available
data, based on conventional sampling and measurement
methods, are discussed first. Results from some pertinent
field programs are surveyed to illustrate the importance
of meteorological processes for the variability of ambient
air pollutants and acid-forming components in precipita-
tion. Results of statistical analyses of data on ambient
concentrations of pollutants are reviewed, and data on
both emissions and deposition are analyzed to infer the
influence of sources on deposition.
Our survey is not a comprehensive one; it focuses on
the results that bear most directly on atmospheric
transport and transformation. In this context, the
issues addressed are whether data are sufficient to infer
(1) the extent to which a given region of sources affects
receptor sites in remote locations and (2) the importance
of nonlinear processes in determining the relationships
between the magnitudes of emissions in source regions and
the quantities of acid-forming substances deposited in
· . ~
receiving regions.
One of the greatest difficulties in establishing
relationships between sources of pollution and conditions
at receptors is accounting for the influences of atmo-
spheric processes on the behavior of pollutants. The
atmospheric processes involved include airflow, mixing,
and chemical transformations. These processes are
responsible, directly or indirectly, for the distribution
and rate of deposition. Attempts to discern the
influences of atmospheric processes on source-receptor
relationships have taken different routes, including (1)
descriptive accounts of observations, (2) analysis of
data segregated by airflow from source areas (trajec-
tories), (3) statistical analyses of data, and (4)
inference from source tracers. In this chapter we
describe the approaches used in these types of analyses
and the results obtained. We also analyze existing data
on emissions and deposition to discern trends and the
relative behavior of sulfur and nitrogen emissions in the
atmosphere.
OCR for page 89
89
AEROMETRIC DATA AND THEIR LIMITATIONS
Most of the historical data on ambient air concentrations
describe urban conditions. A large body of monitoring
data exists in the National Aerometric Data Base (NADB),
but few of these observations have been analyzed or
interpreted. One of the more reliable and complete data
sets available that describes regional air quality in the
eastern United States was taken during a single year,
1977-1978: the Sulfate Regional Experiment (SURE)
(Mueller and Hidy 1983). Unfortunately, few precipita-
tion chemistry data were collected during the period of
the study. In contrast to other data sets, those
obtained from the SURE experiment have been analyzed in
detail. Complementary data are or will be available from
the western United States for 1980-1982 as a result of
several studies (Allard et al. 1981, Pitchford et al.
1981). Observations of precipitation chemistry have bee n
made periodically in the mid-1950s, from 1959 to 1966,
and from 1972 to date in the programs described, for
example, by Wisniewski and Kinsman (1982). Air-quality
and precipitation data have been collected in Canada
since 1974 in the Canadian (CANSAP) monitoring program.
Precipitation data provide a direct measure of we t
deposition. Since there are no direct measurements of
dry deposition, regional patterns are estimated from
ambient concentrations and deposition velocities
(Appendix C). Since deposition velocities depend on the
airflow near the surface, surface properties, and cover,
these calculations are believed to be uncertain for
quantitative evaluation.
The quality of the data describing regional-scale
processes is variable. The precision and accuracy of the
measurements are generally not well defined in work
reported prior to the late 1970s. Recent programs,
however, have made considerable progress in reporting
data with supplemental information on the calibration o f
instruments, as well A: l~h" "rr~rc: ^^n. :~;r`=A ;r' she
observations
. A definitive discussion of aerometric data
is included in Mueller and Hidy (1983). The quality of
recent data on wet deposition is less formally documented,
but extensive information on the comparability of data is
available from the Illinois Water Survey Laboratories,
the Department of Energy's Environmental Measurement
Laboratories in New York, and the Environmental Protec-
tion Agency's Environmental Monitoring Systems Laboratory.
A statistical analysis of data from two independent
OCR for page 90
go
precipitation sampling networks (SURE and MAP3S) covering
a similar region in the eastern United States indicated
that there is good agreement between data on the
concentrations of the major ions, H+, sulfate, nitrate,
and ammonium, between the two networks (Pack 1980).
Documentation of the quality of data is essential to
ensure that comparisons will be possible with data from
future studies. Experiments and monitoring programs
should incorporate such efforts to avoid or at least
minimize controversies about data interpretation. The
integrity of the sampling and analytical methods employed
is another important consideration in measurement quality.
Despite years of effort in the development of methods,
the instrumentation used in past and current programs is
subject to serious interferences. Uncertainties in
results can be large. Interferences or ambiguities in
the methods are particularly serious under rural or
remote conditions, in which concentrations of pollutants
or deposition levels are low.
Listed in Table 4.1 are examples of sampling or mea-
surement uncertainties that exist in currently available
methods of sampling and analysis. From the table it is
evident that few of the important chemically related
measurements can be made without ambiguity because of
uncertainties in the methods.
RELATIONSHIPS AMONG AEROMETRIC PARAMETERS
Atmospheric measurements provide a basic description of
spatial and temporal distributions of pollutants. On a
regional scale, the distribution of SO2 shows strong
gradients near sources, but airborne sulfate shows
relatively weak gradients. Concentrations of both SO2
and SOi are elevated over the industrialized or
urbanized parts of the eastern United States (Figures 4.1
and 4.2). High concentrations of sulfur oxides are found
through the Ohio River Valley into Pennsylvania and New
York to the Atlantic Coast. From this region of high
concentration, there is a strong gradient in ambient
SO2 concentration northeastward toward the Adirondacks,
Vermont, and New Hampshire. The distribution of nitrogen
oxide concentrations is generally similar to that of
sulfur oxides, but it may show more localized maxima near
urban areas (e.g., Mueller and Hidy 1983).
Paralleling the distributions of ambient concentrations
are the distributions of sulfate and nitrate in precipi
OCR for page 91
91
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OCR for page 92
92
~ ~_
J2,~6,\)
I\ . ^?
2(6)
' 7! /~(
20 (601~'
1
~ ~ ,
) ~
~~~4 )
Off
\ ~ _ _ fin
1 _J ~10 ('30)
, - _ lo/ 10 (30)
~ ~\ N ~
_!
j \ 'N
1 \
1
~l
4_ ~
_ _-~
1-Hour
SO2 (ppb)
FIGURE 4.1 Composite spatial distribution of 1-hour average concentrations (ppb)
of SO2 from one representative month in each season between 1977 and 1978. This
average is approximately equivalent to an annual average. Dashed isopleth is based on
limited quantities of SURE data for 1977-1978 and on data taken at Whiteface
Mountain, New York, after 1978. Numbers in parentheses are calculated values of dry
deposition rates in kilograms of sulfur per hectare per year assuming a uniform deposi-
tion velocity of 0.8 cm/s. SOURCE: Data on concentrations from Mueller et al. (1980)
and, for Whiteface Mountain, from V. Mohnen, State University of New York, Albany,
personal communication (1983~.
tation, as indicated in Figures 4.3 and 4.4. These
distributions may be compared with that of the hydrogen
ion concentration in precipitation in Figure 4.5. From
these figures, the pattern of deposition of hydrogen ion
in precipitation appears to correspond to regions of
elevated sulfate and nitrate concentrations. This
finding does not necessarily follow without accounting
for all the cations (such as NH4 and Ca++) and anions that
OCR for page 93
93
7
'it
~_~l
\~z 8 ( '\~ J
~ 24-Hour
c~-~- _;- ~SO4 ("g/m3)
ran ~
a./
.~
FIGURE 4.2 Composite spatial distribution of 24-hour average concentrations of
sulfate (,ug/m3 ~ from one representative month in each season between 1977 and
1978. This average is approximately equivalent to an annual average. Numbers in
parentheses are calculated values of dry-deposition rates in kilograms of sulfur per
hectare per year assuming a uniform deposition velocity of 0.2 cm/s. SOURCE: Data
on concentrations from Mueller et al. (1980~.
may be important factors affecting the acidity of
precipitation.
A qualitative comparison between dry- and
wet-deposition rates can be made from observation.
Wet-deposition rates for sulfate are shown in Figure 4.3
for data taken in 1980. Estimated dry-deposition rates
for SO: and particulates are shown in parentheses in
Figure 4.1 and 4.2 (estimated values in kilograms of
sulfur per hectare per year). The rates have been
calculated using uniform deposition velocities considered
typical of values reported in the literature for SO2
OCR for page 94
94
~4
3 4, ~
l
l ·5.1
i
" ·10
" ·16
I
-
t, v ' \' -
r t - ~
/~6 3 ·5 2-' t
. , 1
t__ j
.~ L-_
49
~48 \
\` · 53"
an, I
?
~37
t~'-~-~w
1 m mole/m2 ~ 0 961 kglha
l
, ._ _ ~ l _ ~1 4
I ·45 ~
t-
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or'_ ~ ~
11 · ~
~]
I
I
2 :~,~!,
-~I' In' ..~-.;..:c..',fyIt.
~ - - ~
\ ,
~ ,
'' 20
FIGURE 4.3 Spatial distribution of mean annual wet deposition of sulfate weighted
by the amount of precipitation in North America in 1980 (mmoles/m2~. SOURCE:
U.S./Canada Work Group #2 (1982~.
gas and for submicrometer particles (sulfate). Note that
in much of the region of high ambient concentrations, dry
deposition apparently dominates total deposition. This
result suggests that dry deposition of SO2 exceeds wet
deposition in parts of the Ohio River Valley and the
Ohio-Pennyslvania-western New York area but becomes
progressively less important farther from the region of
major emissions, to the northeast in New England and
Canada. At large distances from sources, ambient
concentrations of sulfur oxides are low; wet deposition
will dominate dry deposition far from sources if
precipitation is significant.
OCR for page 95
95
~=O.5
_
~ 0. 9, ~
I ~ I
8.2 e/ ~ 3.5
/ ~-
5.5 /
4 ~'\ _q ~1
~ A_
.
t_ _
11~
Of) ~0 Cl i_ _.
~<
;~3~\ '"' 8~.9 ''it
~ _ _ l ' -
I =~
~ <-'9
;W -' to
_ ~
~6.0
~ $43~~\
1 m mole/m2 ~ 0.62 kg/ha
/
FIGURE 4.4 Spatial distribution of mean annual wet deposition of nitrate weighted
by the amount of precipitation in North America in 1980 (mmoles/m2~. SOURCE:
U.S./Canada Work Group #2 (1982~.
THE INFLUENCE OF METEOROLOGICAL CONDITIONS
The spatial distributions of deposition for acid-forming
materials are similar, and elevated concentrations appear
to be associated with areas in which emissions are high.
The temporal behavior of sulfur oxides and nitrogen
oxides is dominated by meteorological variability. For
example, analysis of the SURE data indicates that the
variability in ambient concentrations of SO2 was as
much as an order of magnitude greater than the vari-
ability in SO2 emissions over the eastern United States
(Mueller and Hidy 1983). This finding suggests that
advanced and sophisticated analyses are needed to
separate the influences of emissions from those of
aerometric parameters in such data. These analyses have
OCR for page 96
96
'` .1.0 ~
\ ~
aim_ ;ir;;
TV j i
ret I\.
1~. 5.7 ~ ~ i,>
. ~,
~ 7-- ~
use\
tj ·0.
~\
~ .
· - ~-0 6-'
I ·3.
_ _ _ + _ _ ~ 0 .4
I
~,) ,'
t~o.5 ;
$~ i\
1 m mole/m2 ~ 0.01 kg/ha
= 1-
FIGURE 4.5 Spatial distribution of mean annual wet deposition of hydrogen ion
weighted by the amount of precipitation in North America in 1980 (mmoles/m2 ).
SOURCE: U.S./Canada Work Group #2 (1982~.
followed two directions in the recent literature. The
first is descriptive, taking into account the behavior of
sulfur oxides in the atmosphere as a function of climato-
logical or meteorological features. The second stems
from the first by adapting statistical techniques to
separate influences of different processes. In this
section we review results of analyses of data according
to meteorological conditions and studies of air-mass
trajectories. In the next section we present the results
of statistical methods of analysis.
Classification of Meteorological Conditions
One of the primary conclusions of many studies of field
observations is the absence of a definitive relationship
OCR for page 97
97
between SO2 emissions and sulfate concentrations in dry
air or in precipitation patterns. Sulfur emission rates
are relatively constant, whereas the concentrations of
sulfate aerosol and SC: in the air are highly variable
and dominated by meteorological conditions (Electrical
Power Research Institute 1981). The concentrations of
sulfate particles tend to be high in summer, presumably
because of more rapid photochemical oxidation of SO2,
high in the central and western region of high-pressure
systems that move slowly toward the Atlantic, and high in
maritime tropical air emanating from the coastal region
of the Gulf of Mexico. Concentrations of SC2 also tend
to be high under stagnant air conditions of slow-moving,
high-pressure, anticyclonic systems but tend to be low in
the maritime tropical air. Trajectory analyses applied
to specific transient anticyclonic systems have further
demonstrated the tendency of such systems to favor air-
stagnation situations in which high levels of pollutants
accumulate (King and Vukovich 1982).
Evidence based on chemical and meteorological analyses
as well as satellite photos suggests that, on occasion,
pollutants originating in the Midwest and Northeast can
be entrained in the clockwise flow around a transient
high-pressure system and transported to the Gulf Coast
region. The pollutants are believed then to be adverted
back through the Midwest and Northeast in the south-
westerly flow of maritime tropical air (Wolff et al.
1981, 1982). The slow-moving flow of southwesterly
maritime air from the southern states entrains pollutants
from sources in its path and eventually moves over the
northeastern United States and eastern Canada. Summer-
time convective storms that occur in this air tend to be
quite acidic compared with precipitation during the
cooler months (MAP3S/RAINE Research Community 1982,
Raynor and Hayes 1982a).
Precipitation during autumn, winter, and spring in
eastern North America also tends to occur in moist
southwesterly air that frequently emanates from the
southern states. During these seasons, most of the
precipitation occurs in the vicinity of warm fronts
associated with cyclonic low-pressure storm systems.
Precipitation develops because the southwesterly air
travels faster than the warm front, which represents the
boundary of colder and heavier air lying to the north of
it. The southerly air ascends over the cold air and is
cooled, producing large areas of precipitation. The
situation is illustrated in Figure 4.6. The center of
-
OCR for page 137
137
TABLE 4.9 Molar Ratios of SOx to NOX in the Region of
the SURE Experiment in 1977-1978a
Emissions Ambient Airb
Precipitation
1.2 (all sources) Gas and particles 0.66 0.73 to 1.3
2.2 (utilities)C Gas only 0.42
Particles only 24.0
SOURCE: Adapted from Mueller and Hidy (1983).
aRatio taken as SO2/NO2.
Sated at ground level.
CWeighted heavily toward emissions injected at altitudes at or above 300 m.
concentration data that are averaged over all meteoro-
logical conditions with precipitation data that reflect
only those conditions specifically favoring precipitation.
As indicated earlier, the ratio of sulfate to nitrate
in precipitation varies regularly throughout the year,
being high in summer and low in winter (see Table 4.8).
It is unclear how the specific nrn~=cmc -~1 1 ;~
_ = ~= ~_ _ ~ ~ ~ ~ ~ ~ ^ ~ l y
Renege variations average out annually +^ h" =^ 1ln;.F~-m
spatially and so similar to the emission ratios over much
of the area when ambient atmospheric conditions
apparently are so variable.
Conceivably the uniformity of the annual SO ANON
ratio in precipitation in the northeastern United States
could reflect some as yet unidentified stoichiometric
linkage between the atmospheric chemistry of SO2 and NO2.
For example, the reaction of HOSO2 radicals formed in
reactions of HO with SO2 could lead to HOSO2O2 and HOSO2O
radicals, which could ultimately react preferentially with
NC2 to form a one-to-one, S to N compound such as
HOST ONO2 (see Chapter 3 and Appendix A).
.
This compound
wood an principle hydrolyze in cloud water to form equal
amounts of H2SO4 and HNO3 acids. However, this reaction
mechanism would have to be the dominant ~, rim of on ~
_ HA x~ ~ ~ _ . .
a..- ,~3 ~ ·~nca~n one ratio or moles of SO4 to moles
of NC] near unity, as observe in nr"~;~;' =~;~- :
eastern United States.
rat A- -- ^~ ~=
There is no laboratory or field
evidence of the significant participation of nitryl
sulfuric acid (HOSC2ONC2) or other similar compounds in
acid development; in fact, the existing limited evidence
appears to discount the possible importance of such a
product as an intermediate in the HO-SC:-NOk reaction
system (see Appendix A).
From theoretical considerations (e.g., Chapter 2 and
Appendix A), we expect that ambient concentrations of
oxidants (such as H2O2, C3, and HO) will have
OCR for page 138
138
maximum values in summer and minimum values in winter.
It is expected, therefore, that in winter in areas at
higher latitudes, aqueous oxidation is slow because of
low concentrations of oxidants in cloud water. Hence, if
a limitation of oxidant were to lead to nonlinearity in
the relationship between emissions and deposition, that
effect would be most likely to be observed in winter.
The evidence that the relationship between average annual
emissions and deposition is not strongly nonlinear may
result from the fact that most of the total annual
deposition of acid occurs during the warm months.
Comparison of emission ratios and deposition ratios
constitutes indirect evidence for the absence of a
serious nonlinearity even though we lack an adequate
understanding of the intermediate chemical and meteoro-
logical processes to predict, either qualitatively or
quantitatively, the deposition ratios from the emission
ratios. It is our opinion that the necessary data and
theoretical understanding to model the effects of
emissions from distant sources on the composition of
precipitation reliably and accurately will not be
available in the near future. The evidence based on the
empirical observations appears incompatible with a
seriously nonlinear system in terms of our current
knowledge. Unquestionably, however, it would be
preferable to reinforce such conclusions with a more
complete understanding of atmospheric chemistry and
meteorology under conditions prevalent in eastern North
America.
Additional uncertainties are introduced by the inherent
variabilities of natural processes (e.g., annual rates of
precipitation), imprecision of measurements, and errors
in determining emission rates. For example, the ratios
of emissions and wet depositions in the Northeast are
uncertain by a factor of about 30 percent. The concen-
trations of sulfate and nitrate in the MAP3S study are
estimated to be uncertain by a factor of 15 to 20 percent.
A significant reduction in the uncertainties related
to natural variability, measurement imprecision, or
establishment of emission rates is unlikely in the near
future.
FINDINGS AND CONCLUSIONS
Although data from which to assess the relationships
between emissions and deposition are relatively sparse in
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139
North America, analysis of the available empirical data
provides insight into the nature of the atmospheric
processes involved in acid deposition.
Nonlinearity
Data indicate that the variability in ambient concentra-
tions of SO2 vapor and SO4 particles do not
necessarily correlate with the variability in SO2
emissions but are predominantly controlled by meteoro-
logical conditions. Variations in sulfate particle
concentrations tend to correlate with variations in SO2
vapor concentrations in rural areas of the Northeast.
Regression on principal components and empirical
orthogonal-function analysis suggest that if other
factors were constant, ambient concentrations of SO2
and soi would be determined largely by patterns of
SC2 emissions.
Direct evidence of a strongly nonlinear relationship
between wet deposition of sulfate and SO2 emissions is
limited to extensive historical data in Europe. The
continuous historical record of reasonably reliable data
in North America, at Hubbard Brook, indicates no evidence
for a strongly nonlinear relationship between annual
depositions and annual emissions in the Northeast.
Indirect evidence based on patterns of the ratio of
SO4 to Ned in annual deposition do not support the
hypothesis of a strongly nonlinear relationship between
SO2 emissions and sulfate deposition in eastern North
America. Differences in the relationship between emis-
sions and deposition in Europe and eastern North America
may be the consequence of differences in meteorology,
latitude, or other factors, such as the spatial dis-
tribution of sources, between the two regions.
On the basis of currently available empirical data and
within the limits of uncertainty associated with the data
and with estimating emissions, we therefore conclude that
there is no evidence for a strong nonlinearity in the
relationships between long-term average emissions and
depositions in eastern North America.
The conclusion that nonlinearity is probably not sig-
nificant for annual average deposition in eastern North
America is clouded by three types of uncertainties.
First, direct evidence based on long-term time-series
data is severely limited in North America to only ten
stations, all of which have collected bulk deposition
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140
data. The data from only one site, Hubbard Brook, are
considered to be reasonably reliable. Therefore we have
relied on the historical record at only one station
combined with the indirect evidence provided by data on
sulfate and nitrate deposition compared with SO2 and
NOX emissions. Second, there remain uncertainties in
our detailed understanding of the meteorological, physi
cal, and chemical processes that relate emissions to
deposition. Third, the unknown influences natural vari-
ability in the composition and occurrence of precipi-
tation, imprecision in sampling and analysis, and
uncertainties in estimation of emissions further limit
confidence in this conclusion.
Influence of Local and Distant Sources
Both observational and theoretical evidence exists for
the long-range transport of pollutants leading to acid
deposition. It is apparent that any receptor site will
be influenced to one degree or another by both local and
distant sources. The issue of concern is the extent of
this zone of influence for sensitive ecological areas,
including the relative contributions to deposition of
nearby and distant sources.
In the case of the Hubbard Brook data, the trends in
concentrations of sulfate and nitrate appear to reflect
general trends in emissions. Analyses of the trajectories
of precipitating systems delivering acidic precipitation
to Whiteface Mountain and Ithaca in New York and south
central Ontario in Canada indicate that most of the
acidity in precipitation at these sites--as well as most
of the precipitation--is associated with air masses that
have passed over source regions to the south and
southwest.
The spatial distribution of the annual average molar
ratios of pollutants in emissions and deposition suggest
that atmospheric processes in eastern North America lead
to a thorough mixing of pollutants over a wide geographic
area, making it difficult to distinguish between the
effects of distant and local sources.
On the basis of currently available empirical data, we
cannot in general determine the relative importance for
the net deposition of acids in specific locations of
long-range transport from distant sources or more direct
influences of local sources. We regard the problem of
relating emissions from a given region to depositions in
OCR for page 141
141
a given receptor region to be of primary importance and
recommend that high priority be given to research
relevant to its solution.
The SURE data have indicated a relatively small zone
of influence (of the order of 300 to 600 km) on ambient
sulfate concentrations in general, with occasional
long-range influence during ducting situations involving
southwesterly flows of air. Similarly, warm frontal
precipitation may involve cloud formation in air parcels
adverted for hundreds of kilometers from a southwesterly
direction. The relative contributions of such long-range
effects and of more local regional effects are currently
unknown and cannot be reliably estimated using currently
available models.
REFERENCES
Allard, D.W., I.H. Tombach, H. Mayrsohn, and C.V. Mathai.
1982. Aerosol measurements: western regional air
quality studies. Presented at the 75th Annual Meeting
of the Air Pollution Control Association, New Orleans.
Alpert, D.J., and P.K. Hopke. 1981. A determination of
the sources of airborne particles collected during the
regional air pollution study. Atmos. Environ.
15:675-688.
Altshuller, A.P. 1980. Seasonal and episodic trends in
sulfate concentrations (1963-1978) in the eastern
United States. Environ. Sci. Technol. 14:1337-1348.
Altshuller, A.P., and R.A. Linthurst, ed. 1982. Critical
Assessment Document: The Acidic Deposition Phenomenon
and Its Effects. Draft. Prepared for the U.S.
Environmental Protection Agency. Raleigh, N.C.: The
North Carolina State University Acid Precipitation
Program.
Atkinson, R., A.C. Lloyd, and L. Winges. 1982. An updated
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Representative terms from entire chapter:
eastern north
