EPA-AA-TSS-85- 4
Technical Report
Economic Commission for Europe
Inland Transport Committee
Group of Experts on the Construction of Vehicles
Group of Rapporteurs on Pollution and Energy (GRPE)
New Vehicle Regulation and Emissions
of In-Use Vehicles: The U.S. Experience
By
Philip A. Lorang
August 1983
NOTICE
Technical Reports do not necessarily represent final EPA
decisions or positions. They are intended to present
technical analysis of issues using data which are
currently available. The purpose in the release of such
reports ¦ is to facilitate the exchange of technical
information and to inform the public of technical
developments which may form the basis for a final EPA
decision, position or regulatory action.
Technical Support Staff
Emission Control Technology Division
Office of Mobile Sources
Office of Air and Radiation
U. S. Environmental Protection Agency

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1. INTRODUCTION
The United States was the Eirst nation to regulate emissions
from passenger vehicles and presently has the most stringent
regulations in effect. The U.S. experience of the last IS
years may be useful to other nations as they consider what
their own next regulatory step should be. This paper
describes this experience, with emphasis on the results which
the new vehicle regulations have achieved in terms of
emissions from vehicles in general use by ordinary motorists.
Table 1 shows the exhaust emission standards for hydrocarbons
(HC)t carbon monoxide (CO), and oxides of nitrogen (NOx) that
have applied to vehicles sold in the U.S. each model year.
The standards have been made more stringent in stages, with,
two or more year's between changes in nearly all cases. This
paper will show how emissions of in-use passenger vehicles
have reflected the changes in the new car standards.
The new car standards are enforced initially by a program of
pre-production design review, testing, and certification.
However, there have been three other new car requirements
which have influenced emissions of in-use vehicles. First is
the requirement for new vehicles to pass audits conducted at
the assemblyline, to ensure that vehicles as produced conform
with standards. Second is the requirement that vehicle
manufacturers recall and repair vehicles when the
Environmental Protection Agency (EPA) finds that a
substantial number of similar vehicles fail to meet new car
standards in-use even when properly maintained and operated.
This recall program reduces in-use emissions both through
repair of vehicles subject to an EPA recall order and through
greater manufacturer efforts on all vehicles to avoid the
need for such EPA orders. Third is the requirement, first
applied to 1981 vehicles, that carburetors on new vehicles be
equipped with devices to make adjustment of the idle air/fuel
ratio very difficult. The effects of the audit and recall
programs are difficult to separate from the effect of the new
car emission standards themselves; both programs became fully
operational in the late 1970's, as standards were being made
more stringent. This paper will not attempt to make this
difficult separation. The paper will examine the separate
effect of the requirements regarding the adjustability of the
idle air/fuel mixture.

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2. HYDROCARBONS AND CARBON MONOXIDE
2.1 Steps in Regulation
The U.S. has regulated passengec car emissions since the 1968
model year, but the first HC and CO standards representing
significant control took effect in 1972 and remained in
effect through 1974. The exhaust limits were 3.4 grains per
mile of hydrocarbons and 39 grams per mile of carbon
monoxide. For the first time, the test procedure used a
fully transient driving cycle, mass measurement of emissions,
and included collection and measurement of emissions during a
cold start. Vehicle manufacturers complied with the
1972-1974 standards by calibrating carburetors leaner to.
reduce engine-out emissions of HC and CO, by using air pumps
to inject secondary air into the exhaust stream to promote
further oxidation of HC, and by retarding spark timing to
raise the exhaust temperature to also promote oxidation in
the exhaust stream.
The second step in regulating HC and CO emissions was taken
in 1975. The standards of 1.5 grains per mile HC and 15.0
grams per mile CO established for that year remained in
effect through 1979. These standards caused all domestic and
most foreign manufacturers to apply noble metal, oxidation
catalysts in the exhaust stream. On about two-thirds of new
vehicles produced in these five years, exhaust oxygen needed
to allow combustion of HC and CO in the catalyst was achieved
solely through lean carburetor calibrations. Air pumps were
used on the remainder. With the catalyst to control HC
emissions, it was not necessary to retard spark timing and so
timing calibrations were restored back towards their optimum
values with respect to fuel economy. Of course, lead-free
fuel was required for these catalyst-equipped vehicles.
During the period between 1975 and 1979/ electronic
(point-less) ignition systems also became standard equipment
on most vehicles.
In 1980 the third step	taken, with the HC standard
reduced to 0.41 grams per mile and the CO standard reduced to
7.0 grams per-mile, c^r one year only. The very small number
of vehicles which earlier did not have catalysts were sold
with catalysts in 1- ". In addition, virtually all vehicles
were equipped with -ne of two forms of secondary air
injection: an air ?l-~p system like that used on many earlier
models or the newer pulse air system which uses pressure
fluctuations in the -exhaust ports to draw in air through a
one-way valve. Pulse air systems are cheaper and do not take

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power from the engine. Secondary air injection was necessary
because lean carburetion was no longer sufficient to meet the
reduced standards. Other changes in control methods were
limited to minor calibration adjustments.
In 1981, standards changed again. The HC standard remained
0.41 grams per mile. The CO standard was reduced to 3.4
grams per mile for some vehicles, while many were allowed to
remain at 7.0 until 1983. The more important change was in
the NOx standard, from the 2.0 grams per mile which was in
effect from 1977 through 1980 to only 1.0 grams per mile.
This level made catalytic aftertreatment of NOx essential for
most cars, so three-way catalysts were adopted. In most
cases, closed-loop fuel control via an exhaust gas oxygen
sensor and digital computer was also incorporated to keep the
exhaust gas composition in the range within which three-way
catalysis is possible. Most vehicles retained some form of
secondary air injection, for at least the cold start portion
of operation.
2.2 In-Use Emissions
The first three steps described above have had very evident
impacts on in-use emissions. Each of these steps towards
more stringent regulation of new car emissions has reduced
in-use emissions correspondingly. Figures 1 and 2 compare
the in-use emissions of HC and CO of vehicles produced in
1972-1974, 1975-1979, and 1980. EPA's estimates of the HC
and CO emissions of pre-standards (pre-1968) vehicles are
also shown.
The lines in the figures are derived using linear regression
analysis of data from EPA's In-Use Emission Factor
Surveillance Program. This program periodically borrows
vehicles of various ages from their owners and tests them
with the standard test procedure. Thus, the program measures
emissions of vehicles as they are actually operated and
maintained in-use. Emission data from 5,848 1^72-1980
vehicles are represented in the figures.
Figures 1 and 2 show that each group of vehicles emits less
than the preceding group. In particular, the ca'talyst
technology used on L975-1979 vehicles reduced KC and CO
emissions at low mileage by 50 percent or more compared to
the 1972-1974 vehicles. However, these vehicles do not
perform satisfactorily in comparison to their new car
standards. CO emissions even at low mileage exceed the 1^.0
grams per mile standard. Both HC and CO show rapid increase
with accumulated mileage. EPA investigated the causes of

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this behavior as soon as it was noticed, and determined that
incorrect adjustment of idle air/fuel mixture performed after
shipment from the factory was the major cause. By the time
vehicles were one year old, one-third had been incorrectly
adjusted and the fraction was clearly increasing as vehicles
grew older. Rich air/fuel mixtures caused by incorrect
adjustment increase formation of HC and CO in the engine and
prevent the catalyst from operating due to lack of sufficient
oxygen in the exhaust. EPA therefore initiated regulatory
action to restrict the adjustability of the mixture setting.
This action will be discussed in more detail in Section 2.5
below.
Figures 1 and 2 show that the 1980 vehicles are also,
substantially lower emitting than the 1975-1979 vehicles.
The rate of increase of emissions with age also appears to be
reduced. This improvement came from rather limited and
inexpensive changes in emission control hardware, discussed
previously, and was therefore lower in new vehicle cost per
gram of reduction than the improvement which occurred in
1975. If other countries require control to the level of the
1980 U. S. standards, they would probably do well to spend
less time at the intermediate step (1975-1979 U. S.
standards) than did the U. S.
EPA has tested 1981 and 1982 vehicles in its surveillance
program, but at present the low mileage of these vehicles
makes EPA reluctant to draw firm conclusions for HC and CO.
Although not shown in the figures, the HC and CO data from
these model years are very similar to the lower mileage data
from 1980 vehicles. EPA has found that 1981 and 1982
vehicles can emit large quantities of HC and CO under certain
operating malfunctions but at present the number of such
malfunctions is small.
Trends in ambient pollutant levels are the ultimate test of
whether an air pollution control program has been
successful. Because CO is primarily an automotive pollutant,
ambient CO levels are the best indicator of the success of
the U.S. program of new vehicle regulation. The trend in
U.S. CO levels-since 1975 confirms the improvements suggested
by Figures 1 and 2. From 1975 to 1981, the second highest
8-hour levels of CO have declined by 26 percent. An even
greater improvement was observed in the estimated number of
exceedances of the 8-hour standard, which decreased 84
percent. These improvements generally reflect CO levels at
traffic-saturated monitoring sites in the centers of U.S.
cities, which have experienced little or no change in the
volume of traffic in their vicinity. Consequently, the
improvements in CO levels can be attributed only to
reductions in vehicle emissions.

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Ozone levels, which are partially attributable to automotive
emissions of HC, have also declined in the U.S. From 1975 to
1981, the decline was 14 percent. It is understandable that
the decline in ozone has been smaller than the decline in CO,
since many industrial, commercial and other sources of EC had
not been controlled as of 1981.
2.3 Fuel Economy Trends
The effect of emission standards on fuel economy is a topic
of intense interest, as even a small fuel economy penalty
from more stringent standards can be larger than the cost of
the hardware necessary to comply with the standards. Not
surprisingly, predictions of reduced fuel economy have
preceded nearly all new or more stringent emission standards
in the U. S. Such predictions are troublesome, since the
claimed penalty may be small enough to be within the range of
uncertainty but still large enough to be of social concern.
A retrospective look at fuel economy of U. S. vehicles may be
helpful for other countries. Figure 3 shows actual fuel
economy for each U. S. model year, and the average vehicle
weight for each year. Vehicle weights havfe not been
constant, which obscures true trends in engine efficiency.
Figure 4 therefore adjusts each model year to the mix of
vehicle weights from 1978, an arbitrary year.
Figure 4 shows a slight decline in fuel economy from
pre-standard years through 1974. This is attributable to
reduced compression ratio and to the need to retard spark
timing for control of HC emissions. There was a sudden rise
in fuel economy in 1975, when the use of exhaust catalysts
allowed engine parameters to be recalibrated for better
efficiency. The fact that there was a larger improvement in
1975. than the decline in the previous seven years suggests
that the penalty from spark timing retard and other
calibration compromises was sizable but had been-masked for
several years by other efficiency improvements. The increase
in fuel economy recurred to a lesser extent in 1976 and 1977,
as manufacturers learned the degree to which they could
safely restore optimum engine settings.
When the standards changed again in 1980, fuel economy again
improved after smalL declines in 1978 and 1979 in
contradiction to predictions that the 0.41 grams per mile
hydrocarbon standard would again require compromises with
optimum spark timing for fuel economy.

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rt must be admitted that a comparison of fuel economies from
year to year cannot rule out the possibility that the fuel
economy increase in a given year might have been larger if
the emission standards had not changed. If the standards had
not changed in 1975 and if manufacturers had adopted
catalysts anyway, they would certainly have achieved at least
as much of a fuel economy improvement during 1975 to 1977 and
perhaps more. Indeed, from the buyer's perspective the cost
of the catalyst would have been well worth the fuel savings
it achieved. This possibility does not refute the fact that
catalyst technology itself does not harm fuel economy.
In other countries in which emission standards have resulted
in non-catalyst vehicles with suboptimal engine calibrations,,
catalyst tecnnolcgy can be expected to open the door for fuel
economy improvements worth far more than the additional cost
of the catalyst itself. Catalysts can, of course/ be forced
into use with more stringent standards provided unleaded fuel
is available. However# market demand for fuel efficient
vehicles could by itself also lead manufacturers to adopt
catalysts, again provided unleaded fuel is available.
Accurate fuel economy ratings of new vehicles are essential
for market forces to lead manufacturers'towards greater fuel
economy.
Countries in which emission standards are so. lenient that no
compromises with optimal engine calibrations have been
necessary can adopt catalyst-forcing standards without fear
of a fuel economy penalty, since the catalyst will allow
optimal calibrations to be maintained.
2.4 Improper Use of Leaded Gasoline
In the U. S., the continued public availaility of leaded
gasoline priced lower than unleaded gasoline by $0.05 - 0.07
(U.S.) and with higher octane rating (89 vs 87 typically) has
created an environmental problem. EPA estimates that
presently, about 12 or 13 percent of passenger vehicles
originally equipped with catalysts refuel with leaded
gasoline often enough to seriously and irreversibly damage
the catalyst. Furthermore, improper use of leaded fuel
appears to be more frequent as vehicles get older, so the
overall rate will probably increase as the 1975 and later U.
S. fleet ages towards an equilibrium.
This problem is occurring despite efforts to control it.
Introduction of leaded fuel into a catalyst vehic le by a fuel
station operator is subject to a federal fine of $10,000, but
effective enforcement requires more resources than have yet

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been devoted to it. All catalyst vehicles have devices to
prevent leaded fuel nozzles from being inserted into the fuel
inlet pipe. These devices are easily overcome, however.
The rate of use of leaded fuel and its effect on catalyst
performance ate not so severe as to negate the emissions
benefit of the catalysts that remain operatative. The step
to catalysts in 1975 therefore did have a real environmental
benefit. Nevertheless, the problem of improper use of leaded
fuel needs to be addressed more effectively in the EJ. S., and
other countries should consider how to limit it effectively
from the outset.
2.5 Recent Regulations Concerning Adjustment of Idle Air/Fuel.
Mixture
After EPA discovered that improper adjustments of idle,
air/fuel mixture settings were causing significant increases
in HC and CO emissions of in-use vehicles, it initiated a
rulemaking action to address this problem. The rulemaking
was completed in January 1979, and applied to all 1981 and
later passenger cars and light-duty trucks. The new
regulation, known in the U. s. as the Parameter Adjustment
Regulation, gave EPA authority to adjust the idle setting
(within its adjustable range) on manufactuers' prototype
vehicles before performing the official pre-sale
certification emissions test. To prevent EPA from doing so,
manufacturers sealed the idle air/fuel adjustment screw. The
setting made at the factory can be changed after shipment
only with considerable difficulty.
The new requirement has greatly reduced the frequency of idle
air/fuel mixture adjustments. EPA's surveillance programs
show that only a few percent of 1981 and 1982 vehicles have
received adjustments after shipment from the factory. In
previous model years, the percentage was over fifty within
two or three years of sale* and most adjustments were done
incorrectly. Since 1931, most U. S. passenger vehicles are
equipped with closed-loop fuel metering systems that control
idle air/fuel mixture automatically, so external adjustment
points would ¦have reen mostly obsolete anyway. Therefore,
the experience wi'th restrictions on adjustment of 1981 and
newer vehicles in t: e r_',S. is not immediately relevant to
countries which do r.c" -ave similar closed-loop vehicles.
However, there is earlier U.S. experience which is more
relevant to other countries. General Motors Corporation fGv)
complied with the new regulations on adjustability earlier
than required, in 1979 and 1980. Comparing these GM vehicles
to earlier GM vehicles and to their contemporaries from other

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manufacturers indicates the advantage of preventing improper
adjustment of oxidation catalyst vehicles. The 1979 and 1980
vehicles were manufactured to much different HC and CO
standards, so two separate examples are available. The 1979
GM vehicles, like the 1978 GM vehicles, were manufactured to
standards of 1.5 grams per mile HC and 15 grams per mile CO
and virtually none were equipped with secondary air
injection. The 1980 GM vehicles all were equipped with
secondary air injection to meet the more stringent 0.41 gram
per mile HC and 7.0 gram per mile CO standards. It is very
rare for the idle mixture on 1979 and 1980 GM vehicles to be
adjusted after shipment from the factory. Less than five
percent have been found to have the seals on the adjustment
screws removed.
Figures 5 and 6 compare the HC and CO emissions of 1979 GM
vehicles to those of 1978 GM vehicles and of 1979 vehicles
made by other manufacturers. The lines in the figures are
calculated from data collected in EPA's Emission Factor
Surveillance Program. The 1979 GM vehicles are substantially
lower in HC and CO emissions than either 1978 GM vehicles, or
1979 vehicles produced by other manufacturers. General
Motors and other vehicles from 1979 have approximately the
same emissions at low mileage, but the 1979 GM vehicles
suffer from slower increases in emissions as they get older.
Figure 7 and 8 compare HC and CO emissions of 1980 vehicles
made by GM and all other manufacturers. The low rate of
increase of emissions with increasing age is especially
notable for the GM vehicles. This makes the GM vehicles
lower emitting overall even though at low mileage emissions
from the two groups are about equal. The combination of an
oxidation catalyst, secondary air injection, and an
inaccessible idle air/fuel mixture adjustment appears to be
extremely effective for HC and CO control.
In countries in which manufacturers are accustomed to vehicle
owners and dealers being able to reset idle adjustments after
assembly, manufacturers have limited incentive to make
adjustments correctly during assembly. If seals are placed
on the adjustment mechanism during assembly, it will be
important both for owner satisfaction and air quality that
adjustments be made correctly during assembly. The 1980 GM
vehicles show that this is technically feasible in mass
production.
Since most of the adjustments made on U, S. vehicles after
assembly {i.e., in the field) were incorrect and resulted in

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rich air/fuel mixtures, preventing them from occurring is
believed to have had a beneficial effect on fuel economy.
Studies have shown that the typical improper adjustment
reduces fuel economy in city driving about three percent, and
that at least one-third of vehicles were misadjusted. The
fuel economy benefit should therefore be at least one percent.
3.0	OXIDES OF NITROGEN
3.1	Steps in Regulation
The first U. S. NOx standard was 3.0 grams per mile in 1973,
measured with the 1972 test procedures. When the test
procedure was changed in 1975, the NOx standard was changed,
to 3.1 grams per mile to compensate.. Manufacturers complied
with both standards by using exhaust gas recirculation
(EGR) . The standard was changed to 2.0 grams per mile in
1977, and remained at that level through 1980. Manufacturers
improved the effectiveness of their EGR systems to achieve
this lower standard. During the period of 1973 through 1980,
manufacturers made numerous improvements to reduce the
adverse effect of EGR on driveability and fuel economy. In
1981, most manufacturers added three-way catalysts for
additional NOx control to meet the 1.0 grams per mile
standard.
3.2	In-Use Emissions
Figure 9 shows the NOx emissions of in-use U. S. passenger
cars for pre-standard, 1973-1974, 1975-1980, and 1981-1982
groups. There has been steady reduction. Figure 4 shows
that there was no fuel economy reduction with the
progressively more stringent NOx standards.
3.3	Disablement of EGR Systems
Figure 9 reflects the occurrence of deliberate disablement of
EGR systems on in-use vehicles. The EGR systems on 1973 and
1974 vehicles were crude by current standards, and often had
a noticeable negative effect on driveability and fuel
economy. This' led id high rates of disablement by owners and
service personnel. The belief that EGR systems degrade
vehicle performance has unfortunately lingered in the
consciousness of U. S. motorists and mechanics; even though
major improvements r.ave been made. Recent EPA surveillance
of in-use vehicles has found that about 10 percent of
1975-1982 vehicles have had the EGR system deliberately
disabled. Disablement increases as vehicles get older.

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All manufacturers selling in the U. S. market have by now
developed sophisticated EGR systems which limit recirculation
only to those modes of operations and .flow rates necessary
foe effective NOx control without driveability penalty.
Therefore, another country adopting an NOx standard which
required EGR systems would probably avoid the unfortunate
experience of the U. S. with crude EGR systems in 1973 and
1974. Therefore, public attitudes towards EGR systems should
be less negative in other countries, and the disablement rate
lower.

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Table 1
For
Year
U. S. Standards
Exhaust Emissions From New Gasoline-Fueled
Passenger Vehicles
Test
Procedure [11 Hydrocarbons
Carbon
Monoxide
1968- 1969 7-mode
Oxides of
Nitrogen

50-100 CID
101-140 CID
over 14 0 CID
410 ppm
350 ppm
275 ppm
2.3%
2.0%
1.5%


1970
7-mode
2.2 g/mi
23 g/mi


1971
7-mode
2.2 g/mi
23 g/mi
-

1972
CVS-72
3.4 g/mi
39 g/mi
-

1973- 1974
CVS-7 2
3.4 g/mi
39 g/mi
3.0
g/mi
1975- 1976
CVS-75
1.5 g/mi
15 g/mi
3.1
g/mi
1977- 1979
"CVS-75
1.5 g/mi
15 g/mi
2.0
g/mi
1980
CVS-75
0.41 g/mi
7.0 g/mi
2.0
g/mi
1981 and
later
CVS-75
0.41 g/mi
3.4 g/mi f2J
1.0
g/mi
[1]	Different test procedures have been used since the early years
of emission control which vary in stringency. The appearance
that the standards were relaxed from 1971 to 1972 is
incorrect. The 1972 standards are actually more stringent
because of the greater stringency of the 1972 test procedure.
[2]	Carbon monoxide standard can be waived to 7.0 gpm for 1981-82
by the EPA Administrator.
[3]	Oxides of nitrogen standard can be waived to 2.0 g/rni for
American Motors Corporation for 1981 and 1982 only.

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MILEAGE (10K MILES)
Figure 1 - Hydrocarbon (HC) Emissions of
In-Use Vehicles Produced Under
L'.S. Emissions Standards

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-J. J-
NILEflGE I 1 OK MILES )
Figure 2 - Carbon Monoxide (CO) Emissions of
In-Use Vehicles Produced Under
U.S. Emissions Standards

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-15-
4.0
3.S
3.0
2.5
2 2.0
o
s
0\
\n®>


-*0<*

1.5
1.0
0.5
0.0 ' ' '	I	1	I	I	I	L
0 12 3 4	8 7 8 9 10
MILEflOE ( 10K MILES )
Figure 5 - Hydrocarbon (HC) Emissions of
L978 General Motors (GM) Vehicles,
1979 GM Vehicles, and Other 1979
Vehicles in the U.S.

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MtLEflGE ( 10K MILES )
Figure 6 - Carbon Monoxide (CO) Emissions
of 1978 General Motors (GM)
Vehicles, 1979 GM Vehicles, and
Other 1979 Vehicles in Che U.S.

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Figure 7 - Hydrocarbon (HC) Emissions of
1980 General Motors (GM) Vehicles
and Other 1980 Vehicles in che U.S.

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HILEAGE t 10K MILES )
Figure 8 - Carbon Monoxide (CO) Emissions
of 1980 General Mocors (GM)
Vehicles and Ocher 1980 Vehicles
in the U.S.

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8.0
5.5
5.0
4.5
s«*.o
^ 3.5
(9
w 3.0
X
° 2.5
2.0
1.5
1.0
0.5
0.0
0 1 23458789 10
MILEAGE ( 10K MILES )
Pre-control
1973-1974
T97T-1980
1981-1982
Figure 9 - Oxides of Nitrogen (NOx) Emissions
of In-Use Passenger Vehicles
Under U.S. Emissions Standards

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