A
New
Environmental
Chamber
for
Evaluation
of
Gas­
Phase
Chemical
Mechanisms
and
Secondary
Aerosol
Formation
By
William
P.
L.
Carter*,*,
David
R.
Cocker
III*,*,
Dennis
R.
Fitz*,
Irina
L.
Malkina*,
Kurt
Bumiller*,
Claudia
G.
Sauer*,
¶
,
John
T.
Pisano*,
Charles
Bufalino*,
and
Chen
Song*,*

*
College
of
Engineering
Center
for
Environmental
Research
and
Technology,
University
of
California,
Riverside,
California
92521
*
Department
of
Chemical
and
Environmental
Engineering,
University
of
California,
Riverside,
California
92521
¶
Present
Address:
USP
Indicators,
Suppanstrasse
69,
A­
9020
Klagenfurt,
Austria
*
Corresponding
author
Revised
for
Resubmission
to
Atmospheric
Environment
June
18,
2005
2
Abstract
A
new
state­
of­
the­
art
indoor
environmental
chamber
facility
for
the
study
of
atmospheric
processes
leading
to
the
formation
of
ozone
and
secondary
organic
aerosol
(
SOA)

has
been
constructed
and
characterized.
The
chamber
is
designed
for
atmospheric
chemical
mechanism
evaluation
at
low
reactant
concentrations
under
well­
controlled
environmental
conditions.
It
consists
of
two
collapsible
90
m3
FEP
Teflon
film
reactors
on
pressure­
controlled
moveable
frameworks
inside
a
temperature­
controlled
enclosure
flushed
with
purified
air.
Solar
radiation
is
simulated
with
either
a
200
kW
Argon
arc
lamp
or
multiple
blacklamps.
Results
of
initial
characterization
experiments,
all
carried
out
under
dry
conditions,
concerning
NOx
and
formaldehyde
offgasing,
radical
sources,
particle
loss
rates,
and
background
PM
formation
are
described.
Results
of
initial
single
organic
­
NOx
and
simplified
ambient
surrogate
­
NOx
experiments
to
demonstrate
the
utility
of
the
facility
for
mechanism
evaluation
under
low
NOx
conditions
are
summarized
and
compared
with
the
predictions
of
the
SAPRC­
99
chemical
mechanism.
Overall,
the
results
of
the
initial
characterization
and
evaluation
indicate
that
this
new
environmental
chamber
can
provide
high
quality
mechanism
evaluation
data
for
experiments
with
NOx
levels
as
low
as
~
2
ppb,
though
the
results
indicate
some
problems
with
the
gas­
phase
mechanism
that
need
further
study.
Initial
evaluation
experiments
for
SOA
formation,
also
carried
out
under
dry
conditions,
indicate
that
the
chamber
can
provide
high
quality
secondary
aerosol
formation
data
at
relatively
low
hydrocarbon
concentrations.
3
Introduction
Environmental
chambers
have
been
used
for
the
past
few
decades
to
investigate
processes
leading
to
secondary
pollutant
formation
such
as
ozone
(
Jeffries
et
al,
1982;
1985a­
c;
1990;
Gery
et
al,
1988;
Hess
et
al,
1992;
Simonaitis
and
Bailey,
1995;
Simonaitis
et
al,
1997;
Carter
et
al,

1995a;
Carter,
2000;
Dodge,
2000
and
references
therein)
and
secondary
organic
aerosol
(
SOA).

(
e.
g.,
Odum
et
al.,
1996,
1997;
;
Griffin
et
al.,
1999;
Kleindienst
et
al.,
1999;
Barnes
and
Sidebottom,
2000;
Cocker
et
al.
2001a­
c;
Jang
and
Kamens,
2001;
Seinfeld
and
Pankow,
2003
and
references
therein,
Johnson
et
al,
2004,
Montserrat
et
al,
2005).
These
chambers
are
essential
for
developing
and
evaluating
chemical
mechanisms
or
models
for
predicting
the
formation
of
secondary
pollutants
in
the
absence
of
uncertainties
associated
with
emissions,
meteorology,
and
mixing
effects.
Existing
chambers
have
been
used
to
develop
the
models
now
used
to
predict
ozone
formation
(
Gery
et
al,
1988;
Stockwell
et
al,
1990;
Carter,
2000;
Dodge,
2000
and
references
therein),
and
are
beginning
to
provide
data
concerning
formation
of
SOA
(
e.
g.,
Pandis
et
al.,
1992;
Griffin
et
al.,
2001;
Pun
et
al.,
2003;
Griffin
et
al.,
2003,
Johnson
et
al,
2004,

Montserrat
et
al,
2005).
However,
environmental
chambers
are
not
without
uncertainties
in
characterization
and
variability
and
background
effects
(
Carter
et
al,
1982;
Carter
and
Lurmann,

1991;
Jeffries
et
al,
1992;
Carter
et
al,
1995a;
Dodge,
2000).
This
limits
the
utility
of
the
data
and
the
range
of
conditions
under
which
the
models
or
mechanisms
can
be
reliably
evaluated.

For
example,
because
of
background
effects
and
analytical
limitations,
most
chamber
experiments
to
date
have
been
conducted
using
levels
of
NOx
and
other
pollutants
that
are
significantly
higher
than
those
that
currently
occur
in
most
urban
and
rural
areas
(
Dodge,
2000).

Even
lower
ambient
NOx
conditions
are
expected
as
we
approach
eventual
attainment
of
the
air
quality
standards.
The
nature
of
the
radical
and
NOx
cycles
and
the
distribution
of
VOC
oxidation
products
change
as
absolute
levels
of
NOx
are
reduced.
Because
of
this,
one
cannot
necessarily
be
assured
that
the
current
mechanisms
developed
to
simulate
results
of
relatively
high
concentration
experiments
will
satisfactorily
simulate
downwind
or
cleaner
environments.

Background
effects
can
be
minimized
by
using
large
volume
reactors
and
assuring
that
the
matrix
air
is
adequately
purified,
that
appropriate
wall
material
is
utilized,
and
that
steps
are
4
taken
to
minimize
introduction
of
ambient
pollutants
due
to
leaks
or
permeation.
Large
volume
is
also
required
for
minimizing
wall
losses
of
aerosols
or
semi­
volatile
aerosol
precursors,
which
is
important
in
studies
of
SOA
formation.
For
this
reason,
until
recently,
most
studies
of
SOA
formation
have
been
carried
out
in
large
outdoor
chambers
(
e.
g.,
Jaoui
et
al.,
2004;
Griffin
et
al.,

1999,
Montserrat
et
al,
2005).
However,
outdoor
chambers
have
diurnal,
daily
and
seasonal
changes
in
temperature
and
actinic
flux,
which
can
increase
uncertainties
in
characterization
of
run
conditions
for
model
evaluation
and
make
systematic
studies
of
temperature
and
humidity
effects
difficult.
Recently
a
new
indoor
chamber
was
developed
to
address
these
concerns
(
Cocker
et
al,
2001a),
but
that
chamber
was
not
designed
to
conduct
experiments
characterized
for
low
pollutant
conditions,
and
the
blacklight
light
source
employed
does
not
represent
that
of
natural
sunlight
in
the
longer
wavelength
region
that
affects
some
of
the
photooxidation
processes
(
Carter
et
al,
1995b).

This
paper
describes
a
new
state­
of­
the­
art
environmental
chamber
facility
developed
to
minimize
reactor
effects
in
studies
of
VOC
reactivity
and
provide
a
platform
for
low
NOx
and
VOC
ozone
reactivity
and
secondary
aerosol
formation
experiments.
It
also
provides
the
technical
background
of
the
facility
and
assesses
its
ability
and
limitations
for
low
NOx
experiments.
We
discuss
current
reactor
limitations
and
their
implications
for
studies
on
ozone
reactivity
and
SOA
formation
within
Teflon
reactors.

Facility
Description
The
indoor
facility
comprises
a
6m
x
6m
x
12m
thermally
insulated
enclosure
that
is
continually
flushed
with
purified
air
at
a
rate
of
1000
L
min­
1
and
is
located
on
the
second
floor
of
a
laboratory
building
specifically
designed
to
house
it.
Located
directly
under
the
enclosure
on
the
first
floor
is
an
array
of
gas­
phase
continuous
and
semi­
continuous
gas­
phase
monitors.

Within
the
enclosure
are
two
~
90
m3
(
5.5
m
x
3
m
x
5.5
m)
maximum
volume
2
mil
FEP
Teflon
®
film
reactors,
a
200
kW
Argon
arc
lamp,
a
bank
of
115
W
4­
ft
blacklights,
along
with
the
light
monitoring
and
aerosol
instrumentation.
A
schematic
of
the
enclosure
is
provided
in
Figure
1.
5
Enclosure
The
interior
of
the
thermally
insulated
450
m3
enclosure
is
lined
with
hard
clear
anodized
aluminum
sheeting
to
maximize
the
interior
light
intensity
and
homogenize
the
interior
light
intensity.
A
positive
pressure
is
maintained
between
the
enclosure
and
the
surrounding
room
to
reduce
contamination
of
the
reactor
enclosure
by
the
surrounding
building
air.
The
enclosure
air
is
well
mixed
by
the
large
air
handlers
that
draw
in
air
from
inlets
around
the
light
and
force
the
air
through
a
false
ceiling
with
perforated
reflective
aluminum
sheets.
The
enclosure
is
temperature
controlled
with
a
~
30
ton
(~
105
KW
cooling
power)
air
conditioner
capable
of
producing
a
temperature
range
of
5
to
45
C,
controlled
to
better
than
±
1
C.

Teflon
Reactors
The
2
mil
(
54
µ
m)
FEP
Teflon
®
reactors
are
mounted
within
the
enclosure
with
a
rigid
bottom
frame
and
a
moveable
top
frame.
The
floor
of
the
reactor
is
lined
with
Teflon
®
film
with
openings
for
reactant
mixing
within
and
between
reactors
and
8
ports
ranging
in
size
from
0.64
to
1.3
cm
for
sample
injection
and
withdrawal.
The
moveable
top
frame
is
raised
and
lowered
with
a
motorized
pulley
system,
which
enables
the
user
to
expand
(
during
filling)
and
contract
(
during
an
experiment
or
for
flushing)
the
reactors
as
necessary.
The
rate
of
contraction
or
expansion
is
set
to
maintain
a
differential
pressure
of
5
pascal
between
the
inside
of
the
reactor
and
the
enclosure.
During
experiments,
the
top
frames
are
slowly
lowered
to
maintain
positive
pressure
as
the
volume
decreases
due
to
sampling,
leaks,
and
permeation.
The
experiment
is
terminated
when
the
final
reactor
volume
reaches
1/
3
of
its
maximum
value
(
typically
about
10
hours,
though
less
if
there
are
leaks
in
a
reactor).
The
elevator
system
coupled
with
differential
pressure
measurements
allows
for
repeatable
initial
chamber
volumes
and
allows
for
reactants
to
be
injected
with
greater
than
5%
precision.
The
Teflon
reactors
are
built
in­
house
using
a
PI­
G36
Pac
Impulse
Sealer
(
San
Rafael,
CA)
heat
sealing
device
for
all
major
seams
and
are
mounted
to
the
reactor
floor
and
ceiling.

The
Teflon
reactors
tend
to
eventually
crack
and
leak
after
repeated
use,
with
the
failures
usually
occurring
at
the
seams.
Because
of
the
positive
pressure
control
this
results
in
shorter
times
for
experiments
rather
than
dilution
or
contamination
of
the
reactor.
Leaks
are
repaired
6
using
a
polyester
film
tape
with
a
silicone
adhesive
(
3M
Polyester
Tape
8403)
when
needed,
and
the
reactors
are
repaired
periodically
before
leaks
and
repairs
become
excessive.

Pure
Air
System
An
Aadco
737
series
(
Cleves,
Ohio)
air
purification
system
produces
compressed
air
at
rates
up
to
1500
L
min­
1.
The
air
is
further
purified
by
passing
through
canisters
of
Purafil
®
and
heated
Carulite
300
®
followed
by
a
filter
pack
to
remove
all
particulate.
The
purified
air
within
the
reactor
has
no
detectable
non­
methane
hydrocarbons
(<
1
ppb),
NOx
(<
10
ppt),
no
detectable
particles
(<
0.2
particles
cm­
3),
and
a
dew­
point
below
­
40
C.

All
the
experiments
discussed
in
this
paper
were
carried
out
with
unhumidified
air,
i.
e.,

with
a
dew
point
below
­
40
C.
A
humidification
system
has
now
been
constructed,
and
this
system
and
results
of
humidified
experiments
will
be
discussed
in
a
subsequent
paper.

The
reactors
are
cleaned
between
runs
by
reducing
the
reactor
volume
to
less
than
5%
of
its
original
volume
and
re­
filling
it
to
its
maximum
volume
with
purified
air
at
least
six
times.
No
residual
hydrocarbons,
NOx,
or
particles
are
detected
after
the
cleaning
process.

Light
sources
A
200
kW
Argon
arc
lamp
with
a
spectral
filter
(
Vortek
co,
British
Columbia,
Canada)
is
used
as
the
primary
means
to
irradiate
the
enclosure
and
closely
simulate
the
entire
UV­
Visible
ground­
level
solar
spectra.
The
arc
lamp
is
mounted
on
the
far
wall
from
the
reactors
at
a
minimum
distance
of
6m
to
provide
uniform
lighting
within
both
reactors.
Backup
lighting
is
provided
by
banks
of
total
80
1.22
m,
115­
W
Sylvania
350BL
blacklamps
(
peak
intensity
at
350
nm)
mounted
on
the
same
wall
of
the
enclosure.
These
provide
a
low­
cost
and
efficient
UV
irradiation
source
within
the
reactor
for
experiments
where
the
closer
spectral
match
provided
by
the
Argon
arc
system
is
not
required.
The
light
spectra
and
intensity
characterization
for
these
sources
are
discussed
below.
7
Interreactor
and
Intrareactor
mixing
The
two
reactors
are
connected
to
each
other
through
a
series
of
custom
solenoid
valves
and
blowers.
The
system
provides
for
rapid
air
exchange
prior
to
the
start
of
an
experiment
ensuring,
that
both
reactors
have
identical
concentrations
of
starting
material.
Each
reactor
can
be
premixed
prior
to
the
start
of
an
experiment
by
Teflon
coated
fans
located
within
the
reactor.

Instrumentation
The
suite
of
traditional
and
non­
traditional
instruments
used
to
monitor
gaseous
species
within
the
reactors
complete
with
species
detected
and
detection
limits
is
listed
and
briefly
described
Table
1.
All
gas­
phase
instruments
are
located
directly
below
the
enclosure
on
the
first
floor
of
the
building.

The
aerosol
phase
instrumentation
present
is
also
included
in
Table
1,
and
is
similar
to
that
described
by
Cocker
et
al.
(
2001a).
Particle
size
distributions
are
obtained
using
a
scanning
electrical
mobility
spectrometer
(
SEMS)
(
Wang
and
Flagan,
1990)
equipped
with
a
3077
85Kr
charger,
a
3081L
cylindrical
long
column,
and
a
3760A
condensation
particle
counter
(
CPC).

Flow
rates
of
2.5
LPM
and
0.25
LPM
for
sheath
and
aerosol
flow,
respectively,
are
maintained
using
Labview
6.0­
assisted
PID
control
of
MKS
proportional
solenoid
control
valves
and
relating
flow
rate
to
pressure
drop
monitored
by
Honeywell
pressure
transmitters.
Both
the
sheath
and
aerosol
flow
are
obtained
from
the
reactor
enclosure.
The
data
inversion
algorithm
described
by
Collins
et
al
(
2001)
converts
CPC
counts
versus
time
to
number
distribution.
In
addition,
a
tandem
differential
mobility
analyzer
(
TDMA)
is
available
to
measure
physical
changes
to
aerosol
withdrawn
from
the
chamber
due
to
chemical
or
physical
(
temperature)

changes
in
its
environment
(
Cocker
et
al,
2001a).

Characterization
Results
Light
Characterization
Photolysis
rates
used
when
modeling
chamber
experiments
are
calculated
using
the
measured
NO2
photolysis
rates,
the
relative
measured
spectral
distributions
for
the
light
sources,
8
and
the
absorption
cross
sections
and
quantum
yields
for
NO2
and
the
other
photolysis
reactions
in
the
chemical
mechanism
being
evaluated.
Therefore
the
measured
NO2
photolysis
rates
serve
as
the
measure
of
the
absolute
light
intensity,
and
the
relative
spectral
distributions
of
the
light
sources
serve
as
the
means
to
calculate
the
other
photolysis
rates
relative
to
that
for
NO2.
The
precisions
of
the
photolysis
rates
so
derived
are
determined
primarily
by
the
precision
of
the
NO2
actinometry
measurement.
These
are
described
below.

Argon
arc
lamp
Although
the
intensity
of
the
argon
arc
light
can
be
varied
by
varying
the
lamp
power,

normally
it
is
operated
at
57%
power,
including
all
the
experiments
discussed
here.
Information
about
trends
in
light
intensity
with
time
is
available
from
data
from
the
spectral
radiometer
and
PAR
radiation
instruments
(
Table
1),
and
from
results
of
NO2
actinometry
experiments
carried
out
periodically
using
the
quartz
tube
method
of
Zafonte
et
al
(
1977)
modified
as
discussed
by
Carter
et
al
(
1995a).
The
results
indicated
no
significant
change
of
light
intensity
with
time
during
the
period
the
chamber
has
been
operated.
Experiments
with
the
quartz
tube
located
inside
the
reactors
yielded
an
NO2
photolysis
rate
of
0.26
±
0.01
min­
1.

The
relative
spectrum
of
the
arc
light
source
was
measured
using
a
LI­
COR
LI­
1800
spectroradiometer,
and
is
shown
on
Figure
2.
(
The
data
are
normalized
to
the
same
NO2
photolysis
rate
because
that
is
how
they
are
used
to
derive
photolysis
rates
in
the
experiments.

The
instrument
does
not
measure
the
spherically
integrated
absolute
intensities
needed
to
directly
calculate
photolysis
rates,
but
its
data
are
useful
for
relative
measurements.)
No
appreciable
change
in
the
light
source
spectrum
was
observed
in
the
first
18
months
of
operation.

Blacklamps
A
series
of
NO2
actinometry
measurements
inside
the
reactors
with
blacklight
irradiation
were
carried
out
in
April­
May
of
2003
and
again
in
October
of
that
year,
and
the
averages
of
the
results
were
0.19
and
0.18
min­
1,
respectively.
Relative
light
intensity
data
taken
during
blacklight
experiments
indicated
a
gradual
decreasing
trend
in
light
intensity
during
the
experiments
that
was
consistent
with
the
differences
between
these
two
measurements.
This
gradual
decrease
in
intensity
with
time
is
consistent
with
our
experience
with
other
blacklight
9
chambers
(
e.
g.,
see
Carter
et
al,
1995a).
The
uncertainty
in
the
NO2
photolysis
rate
assignments
are
estimated
to
be
~
5%.
The
spectrum
of
this
light
source
was
essentially
the
same
as
that
recommended
by
Carter
et
al
(
1995a)
for
modeling
blacklight
chamber
runs,
as
shown
in
Figure
1,
and
did
not
change
with
time.

Characterization
of
Contamination
by
Outside
Air
Minimizing
contamination
of
the
reactor
by
leaks
and
permeation
of
laboratory
air
contaminants
was
an
important
design
goal
of
the
new
reactors.
This
is
accomplished
by
providing
clean
air
within
the
enclosure
that
houses
the
reactors.
Continuous
monitoring
of
the
enclosure
contents
demonstrates
that
NOx
and
formaldehyde
levels
in
the
enclosure
before
or
during
irradiations
are
less
than
5
ppb
and
PM
concentrations
are
below
the
detection
limits
of
our
instrumentation
(
see
Table
1).
Introduction
of
contaminants
into
the
reactor
is
also
minimized
by
use
of
pressure
control
to
assure
that
the
reactors
are
always
held
at
slight
positive
pressures
with
respect
to
the
enclosure.
Thus
leaks
are
manifested
by
reduction
of
the
reactor
volume
rather
than
dilution
of
the
reactor
by
enclosure
air.
The
leak
rate
into
the
chamber
was
tested
by
injecting
~
100
ppm
of
CO
into
the
enclosure
and
monitoring
CO
within
the
reactor
for
more
than
6
hours.
In
addition,
since
CO
is
a
small
molecule,
it
should
provide
an
upper
limit
of
leak
plus
permeation
into
the
reactor.
No
appreciable
CO
(
above
the
50
ppb
detection
limit)
was
obtained
for
this
experiment.
Therefore
it
was
concluded
that
leaks/
permeation
into
the
chamber
is
negligible
for
the
current
reactor
configuration.

Chamber
Effects
Characterization
It
is
critical
to
understand
the
impact
of
reactor
walls
on
gas­
phase
reactivity
and
secondary
aerosol
formation.
Larger
volume
reactors
may
minimize
these
effects,
but
they
cannot
be
eliminated
entirely
or
made
negligible.
For
mechanism
evaluation
and
SOA
studies
the
most
important
of
these
effects
include
background
offgasing
of
NOx
and
other
reactive
species,

offgasing
or
heterogeneous
reactions
that
cause
"
chamber
radical
sources"
upon
irradiation
(
e.
g.,

see
Carter
et
al,
1982),
ozone
and
particle
losses
to
the
reactor
walls,
and
background
offgasing
of
PM
or
PM
precursors.
Most
of
these
can
be
assessed
by
conducting
various
types
of
characterization
experiments
that
either
directly
measure
the
parameter
of
interest,
or
are
highly
10
sensitive
to
the
chamber
effect
being
assessed
(
e.
g.,
see
Carter
et
al,
1995a).
The
chamber
effects
relevant
to
gas­
phase
mechanism
evaluation
that
have
been
assessed
and
the
types
of
experiments
utilized
for
assessing
them
are
summarized
in
Table
2.
These
are
discussed
further
below.

Note
that
as
indicated
in
Table
2
some
of
the
chamber
characterization
parameters
are
derived
by
conducting
model
simulations
of
the
appropriate
characterization
experiments
to
determine
which
parameter
values
best
fit
the
data.
All
the
characterization
simulations
discussed
here
were
carried
out
using
the
SAPRC­
99
chemical
mechanism
(
Carter,
2000)
with
the
photolysis
rates
calculated
using
the
light
characterization
data
discussed
above,
using
the
measured
temperatures
of
the
experiments,
and
assuming
no
dilution
for
reasons
discussed
in
the
previous
section.
The
rates
of
heterogeneous
reactions
not
discussed
below,
such
as
N2O5
hydrolysis
to
HNO3
or
NO2
hydrolysis
to
HONO,
were
derived
or
estimated
based
on
laboratory
studies
or
other
considerations
as
discussed
by
Carter
et
al
(
1995a).
Although
the
assumed
values
of
these
parameters
can
affect
model
simulations
under
some
conditions,
they
are
not
considered
to
be
of
primary
importance
in
affecting
simulations
of
the
characterization
or
other
experiments
discussed
here.

NOx
offgasing
NOx
offgasing
is
the
main
factor
limiting
the
utility
of
the
chamber
for
conducting
experiments
under
low
NOx
conditions.
Although
this
can
be
derived
by
directly
measuring
increases
in
NOx
species
during
experiments
when
NOx
is
not
injected,
the
most
sensitive
measure
is
the
formation
of
O3
in
irradiations
when
VOCs
but
not
NOx
are
initially
present.

Therefore,
the
NOx
offgasing
rate
is
not
determine
directly,
but
derived
by
determining
the
magnitude
of
the
NOx
offgasing
rates
that
it
is
necessary
to
assume
in
the
chamber
effects
model
for
the
model
simulations
of
the
experiments
to
correctly
predict
the
experimentally
observed
O3
yields.
The
NOx
offgasing
can
be
represented
in
the
model
as
inputs
of
any
species
that
rapidly
forms
NOx
in
atmospheric
irradiation
systems,
such
as
NO,
NO2,
or
HONO
(
which
rapidly
photolyzes
to
form
NO,
along
with
OH
radicals),
but
for
reasons
discussed
below
it
is
represented
in
our
chamber
effects
model
as
offgasing
of
HONO,
e.
g.,

Walls
+
h 
 
HONO
Rate
=
k1
x
RN
(
1)
11
Where
k1
is
the
light
intensity
as
measured
by
the
NO2
photolysis
rate,
and
RN
is
the
NOx
(
and
radical)
offgasing
parameter,
which
is
derived
by
model
simulations
of
the
appropriate
characterization
experiments
to
determine
which
value
best
fits
the
data.

The
NOx
offgasing
rates
necessary
to
use
in
the
model
simulations
to
predict
the
observed
O3
formation
rates
in
the
CO
­
air,
formaldehyde
­
air
and
CO
­
formaldehyde
­
air
experiments
carried
out
in
the
first
eight
months
of
operation
of
this
chamber
are
shown
as
the
triangle
symbols
in
Figure
3.
The
plots
are
against
the
EPA
chamber
experimental
run
number,
which
indicates
the
order
that
the
experiment
was
carried
out.
It
can
be
seen
that
the
rates
of
around
1.5
ppt/
min
generally
fit
the
data
up
to
around
run
85,
then
these
increased
to
2­
7
ppt/
min
after
that,

being
somewhat
higher
in
the
"
A"
reactor
compared
to
the
"
B"
reactor.
The
reason
for
this
increase
is
unclear,
but
it
may
be
related
to
the
fact
that
maintenance
was
done
to
the
reactors
around
the
time
of
the
change.
The
magnitudes
of
these
apparent
NOx
offgasing
rates
are
discussed
further
below
in
conjunction
with
the
discussion
of
the
continuous
radical
source,

which
is
also
attributed
to
HONO
offgasing.

Chamber
radical
source
It
has
been
known
for
some
time
that
environmental
chamber
experiments
could
not
be
modeled
consistently
unless
some
sources
of
radicals
attributed
to
chamber
effects
is
assumed
(
e.
g.,
Carter
et
al,
1982;
Carter
and
Lurmann,
1991;
Carter,
2000).
The
most
sensitive
experiments
to
this
effect
are
NOx
­
air
irradiations
of
compounds,
such
as
CO
or
alkanes,
which
are
not
radical
initiators
or
do
not
form
radical
initiating
products
to
a
sufficient
extent
to
significantly
affect
their
photooxidations.
If
no
chamber
dependent
radical
source
is
assumed,

model
simulations
of
those
experiments
predict
only
very
slow
NO
oxidation
and
essentially
no
O3
formation,
while
in
fact
the
observed
NO
oxidation
and
O3
formation
rates
are
much
higher
(
Carter
et
al,
1982).
It
is
necessary
to
assume
unknown
or
chamber­
dependent
radical
sources
for
the
model
to
appropriately
simulate
the
results
of
these
experiments.

In
some
chambers
at
least
part
of
the
chamber­
dependent
radical
source
can
be
attributed
to
formaldehyde
offgasing
(
Simonaitis
et
al,
1997,
Carter,
2004),
but
as
discussed
below
the
magnitude
of
the
formaldehyde
offgasing
in
this
chamber
is
relatively
small,
and
not
sufficient
12
by
itself
for
the
model
to
simulate
radical­
source
dependent
experiments.
For
this
chamber,

assuming
HONO
offgasing
at
a
similar
magnitude
as
the
apparent
NOx
offgasing
rate
derived
as
discussed
above
is
usually
sufficient
to
account
for
most
of
the
chamber­
dependent
radical
source,
though
results
of
some
of
the
experiments
are
somewhat
better
simulated
if
a
small
amount
(
100
ppt
or
less)
of
HONO
is
also
assumed
to
be
initially
present.

The
round
symbols
in
Figure
3
shows
plots
of
the
HONO
offgasing
rates
that
are
necessary
to
assume
in
the
model
simulations
for
the
model
to
simulate
the
NO
oxidation
and
O3
formation
rates
in
the
radical­
source
sensitive
CO
­
NOx
and
n­
butane
­
NOx
experiments
that
were
carried
out
in
January­
October
of
2003.
Note
that
since
these
experiments
had
initial
NOx
levels
ranging
from
10
­
200
ppb,
so
they
were
not
sensitive
to
NOx
offgasing
as
such.
However,

from
Figure
3
it
can
be
seen
that
the
magnitudes
of
the
NOx
offgasing
and
continuous
radical
input
rates
that
fit
the
data
for
the
respective
characterization
experiments
were
in
the
same
range,
and
even
changed
at
the
same
time
when
the
characteristics
of
the
chamber
apparently
changed.
Whatever
effect
or
contamination
caused
the
apparent
NOx
offgasing
to
increase
around
the
time
of
run
85
caused
the
same
increase
in
the
apparent
radical
source.

Comparison
of
Radical
Source
and
NOx
Offgasing
with
Other
Chambers
Although
HONO
is
not
measured
directly
in
our
experiments,
the
fact
that
both
the
radical­
sensitive
and
NOx­
sensitive
characterization
experiments
can
be
simulated
assuming
HONO
offgasing
at
approximately
the
same
rates
is
highly
suggestive
that
this
is
the
process
responsible
for
both
effects.
Direct
evidence
for
this
comes
from
the
data
of
Rohrer
et
al
(
2004),

who
used
sensitive
long
path
absorption
photometer
(
LOPAP)
instrument
to
detect
ppt
levels
of
HONO
emitted
from
the
walls
during
irradiations
in
the
large
outdoor
SAPHIR
chamber
(
Brauers
et
al,
2003)
at
rates
comparable
to
those
observed
in
the
earlier
experiments
in
our
chamber.
The
SAPHIR
chamber
is
similar
in
design
to
our
chamber,
except
it
is
larger
in
volume
and
is
located
outdoors.
In
particular,
like
our
chamber
it
has
Teflon
walls
and
uses
an
enclosure
configuration
to
minimize
contamination
by
outside
air.
Therefore,
it
would
be
expected
to
have
similar
chamber
NOx
and
radical
sources,
and
this
appears
to
be
the
case.
13
Figure
4
shows
plots
of
the
NOx
offgasing
or
radical
source
parameter
(
e.
g.
RN
in
Equation
1)
obtained
in
modeling
appropriate
characterization
runs
in
various
chambers,
where
they
are
compared
with
direct
measurements
made
in
the
SAPHIR
chamber
(
Rohrer
et
al,
2004).

In
addition
to
those
for
this
UCR
EPA,
the
radical
source
parameters
shown
are
those
derived
by
Carter
(
2000)
for
previous
indoor
and
outdoor
chambers
at
UCR
(
Carter
et
al,
1995a),
those
derived
by
Carter
and
Lurmann
(
1991)
for
the
University
of
North
Carolina
(
UNC)
outdoor
chamber
(
Jeffries
et
al,
1982,
1995a­
c,
1990),
and
those
derived
by
Carter
(
2004)
for
the
Tennessee
Valley
Authority
(
TVA)
indoor
chamber
(
Simonaitis
and
Bailey,
1995;
Bailey
et
al,

1996).
(
Note
that
the
data
shown
for
the
UCR
EPA
chamber
includes
experiments
carried
out
subsequently
to
those
shown
in
Figure
3,
including
a
few
runs
at
reduced
temperature.)
The
figure
shows
that
the
radical
source
and
NOx
offgasing
rates
derived
for
this
chamber
are
comparable
in
magnitude
to
the
HONO
offgasing
directly
measured
in
the
SAPHIR
chamber
and
also
comparable
to
the
NOx
offgasing
derived
for
TVA
chamber
but
are
significantly
lower
than
those
derived
from
modeling
characterization
data
from
the
earlier
UCR
and
UNC
chambers.
It
is
interesting
to
note
that
parameters
derived
for
the
various
chambers
indicate
that
the
radical
source
and
HONO
or
NOx
offgasing
rates
all
increase
with
temperature.

Therefore,
the
radical
source
and
NOx
offgasing
rates
indicated
by
the
characterization
data
for
the
first
series
of
experiments
for
this
chamber
is
probably
as
low
as
one
can
obtain
for
reactors
constructed
of
FEP
Teflon
film,
which
is
generally
believed
to
be
the
most
inert
material
that
is
practical
for
use
as
chamber
walls.
Although
the
radical
source
and
NOx
offgasing
rates
for
the
second
series
of
experiments
is
higher
(
see
also
Figure
3),
they
are
still
about
an
order
of
magnitude
lower
than
observed
for
the
UCR
and
UNC
chambers
previously
used
for
mechanism
evaluation.

Formaldehyde
offgasing
Low
but
measurable
amounts
of
formaldehyde
were
formed
in
irradiations
in
this
chamber,
even
in
pure
air,
CO
­
NOx,
or
other
experiments
where
no
formaldehyde
or
formaldehyde
precursors
were
injected,
and
where
formaldehyde
formation
from
the
reactions
of
methane
in
the
background
air
is
predicted
to
be
negligible.
The
data
in
essentially
all
such
experiments
could
be
modeled
assuming
a
continuous
light­
dependent
formaldehyde
offgasing
14
rate
corresponding
to
0.3
ppb/
hour
at
the
light
intensity
of
these
experiments.
Formaldehyde
levels
resulting
from
this
relatively
low
offgasing
rate
could
not
be
detected
with
formaldehyde
analyzers
used
in
most
previous
UCR
and
other
chamber
experiments,
and
are
insufficient
to
account
for
the
apparent
chamber
radical
source
observed
in
most
chamber
experiments.
This
apparent
formaldehyde
offgasing
has
a
non­
negligible
effect
on
very
low
VOC
and
radical
source
characterization
experiments,
so
it
must
be
included
in
the
chamber
characterization
model.
However,
it
has
a
relatively
minor
impact
on
modeling
most
experiments
used
for
VOC
mechanism
evaluation
or
reactivity
assessment.

The
source
of
the
apparent
formaldehyde
offgasing
in
the
Teflon
reactors
is
unknown,
but
it
is
unlikely
to
be
due
to
buildup
of
contaminants
from
previous
exposures
or
contamination
from
the
enclosure.
The
apparent
formaldehyde
offgasing
rate
is
quite
consistent
in
most
cases
and
there
are
no
measurable
differences
between
the
two
reactors.
This
is
despite
the
fact
that
the
East
or
"
Side
B"
reactor
was
constructed
several
months
after
the
West
or
"
Side
A"
reactor,

which
was
used
in
at
least
17
experiments
before
the
second
reactor
was
built.
In
addition
the
background
formaldehyde
level
in
the
enclosure
was
quite
variable
during
this
period,
and
no
apparent
correlation
between
this
and
the
apparent
formaldehyde
offgasing
rates
in
the
reactor
was
observed.
The
data
are
best
modeled
by
assuming
only
direct
formaldehyde
offgasing,
as
opposed
to
some
formaldehyde
being
formed
from
light­
induced
reactions
of
some
undetected
contaminant.

Other
Reactive
VOC
Background
or
Offgasing
Because
of
limitations
in
the
detection
and
sensitivity
of
the
organic
monitoring
methods
currently
available
with
our
chamber,
characterization
experiments
that
are
sensitive
to
background
reactive
VOCs
provide
the
most
useful
means
to
assess
whether
background
levels
or
offgasing
of
other
reactive
VOCs
are
significant.
Ozone
formation
in
pure
air
runs
is
very
sensitive
to
background
reactive
VOCs,
though
it
is
also
sensitive
to
the
NOx
offgasing
effects
discussed
above.
The
average
6­
hour
ozone
levels
in
the
pure
air
runs
carried
out
with
the
arc
lights
during
this
period
with
the
chamber
in
the
standard
configuration
was
only
4
±
2
ppb.
This
can
be
compared
with
the
model
simulations
of
the
same
experiments,
using
the
NOx
and
formaldehyde
offgasing
parameters
derived
from
the
other
characterization
experiments
as
15
discussed
above,
and
assuming
no
other
reactive
VOCs
are
present,
which
gave
an
average
6­

hour
O3
of
6
±
2
ppb.
This
indicates
that
background
or
offgasing
of
other
reactive
VOCs
is
not
significantly
affecting
results
of
these
experiments,
and
should
have
even
smaller
effects
on
mechanism
evaluation
experiments
with
added
reactive
VOCs.

Particle
wall
losses
Particle
wall
losses
are
expected
in
finite
volume
reactors
and
are
somewhat
enhanced
by
the
charged
surfaces
of
the
Teflon
media.
Particle
wall
losses
within
chambers
have
been
described
in
detail
in
Cocker
et
al.
(
2001a).
Briefly,
wall
losses
are
expected
to
be
described
by
a
first
order
wall
loss
mechanism
with
a
weak
size
dependence
for
the
aerosol
sizes
typical
of
SOA
experiments.
Particle
wall
loss
rates
can
be
determined
in
any
experiment
where
particles
are
present
for
a
sufficiently
long
time
that
new
particle
formation
is
no
longer
determining.
If
it
is
assumed
that
no
new
particle
formation
is
occurring,
then
the
decay
rate
in
the
particle
number
can
be
assumed
to
be
the
particle
loss
rate.

Figure
5
shows
plots
of
particle
wall
loss
obtained
from
data
from
various
experiments
in
this
chamber
from
the
time
particle
measurements
were
made
through
the
summer
of
2004.
It
can
be
seen
that
although
there
is
run­
to­
run
variability,
the
decay
rates
are
reasonably
consistent
at
approximately
7
day­
1,
with
no
significant
differences
among
reactors.
This
is
within
the
range
reported
for
other
large
chamber
facilities
(
Barnes
and
Sidebottom,
2000,
Griffin,
1999).
While
the
maximum
particle
volume
in
the
experiments
ranged
from
less
than
0.1
to
almost
80
µ
g/
m3,

there
was
no
correlation
between
maximum
particle
volume
and
measured
decay
rate.

Background
Particle
Formation
The
reactor
walls
could
be
a
source
of
particles
as
well
as
gas­
phase
species.
This
could
be
due
to
either
direct
release
of
particles
from
the
walls
during
the
irradiations,
or
offgasing
of
compounds
that
react
to
form
secondary
PM.
Background
PM
formation
could
also
occur
if
there
were
impurities
in
the
air
that
reacted
to
form
secondary
PM.
This
would
be
manifested
by
the
formation
of
particles
in
pure
air
irradiations
or
irradiations
of
reactants
that
are
not
expected
to
form
condensable
products.
16
Maximum
PM
number
and
PM
volume
levels
measured
after
5
hours
of
irradiation
in
pure
air,
CO
­
air,
CO
­
NOx
­
air,
and
propene
­
NOx
experiments
carried
out
in
the
second
set
of
reactors,
installed
immediately
before
run
169,
are
shown
on
Figure
6.
(
Characterization
data
for
the
first
set
of
reactors
are
sparse
but
generally
consistent
with
the
results
shown
here.)

Measurable
PM
formation
is
seen
in
pure
air
and
propene
­
NOx
experiments,
but
essentially
no
PM
formation
is
seen
in
the
CO
­
air
or
CO
­
NOx
irradiations.
The
lack
of
measurable
PM
in
the
CO
­
air
or
CO
­
NOx
experiments
suggests
that
PM
is
not
directly
emitted
from
the
irradiated
walls,
though
this
is
considered
to
be
unlikely
in
the
first
place.
The
fact
that
background
PM
is
formed
in
the
pure
air
and
propene
­
NOx
experiments
but
not
the
CO
­
air
or
CO
­
NOx
experiments
could
be
attributed
to
PM
formation
from
the
reaction
of
OH
radicals
with
some
background
contaminant(
s).
Model
calculations
predict
that
OH
levels
are
suppressed
in
the
CO
experiments
because
of
its
reaction
with
CO
combined
with
the
lack
of
homogeneous
radical
sources
in
CO
­
air
or
CO
­
NOx
systems.

The
background
PM
in
the
pure
air
and
propene
­
NOx
experiments
is
the
highest
when
the
rectors
were
new,
and
eventually
decline
as
the
reactor
is
used.
This
suggests
that,
at
least
for
these
reactors,
contaminants
due
to
the
experiments
are
less
important
than
contaminants
on
the
new
Teflon
film
or
that
are
introduced
during
its
construction.
The
apparent
background
PM
in
eventually
declined
in
both
reactors,
becoming
very
low
in
Reactor
B,
but
continued
to
be
nonnegligible
in
Reactor
A.
Reactor
A
also
had
higher
levels
of
background
PM
at
the
start.

Although
the
reaction
of
O3
with
background
contaminants
could
be
another
source
of
background
PM,
this
does
not
appear
to
be
as
significant
in
this
chamber.
Higher
levels
of
O3
are
formed
in
CO
­
air
than
in
pure
air
runs,
yet
the
PM
levels
are
much
lower
in
the
presence
of
CO.

PM
levels
in
O3
dark
decay
experiments
are
relatively
low.
In
particular,
the
PM
volume
in
the
0.2
ppm
O3
dark
decay
experiment
179
was
only
~
0.1
µ
g/
m3
in
both
reactors
after
~
5
hours,

despite
the
fact
that
this
was
during
period
with
new
reactors
when
the
background
was
relatively
high.
The
PM
levels
increased
only
slightly
when
O3
was
irradiated.
17
Initial
Experiments
Gas­
Phase
Characterization
and
Mechanism
Evaluation
Experiments
Table
3
gives
a
summary
of
the
initial
experiments
carried
out
in
this
chamber
for
gasphase
characterization
and
mechanism
evaluation.
All
these
experiments
were
carried
with
unhumidified
air
(
dew
point
<
­
40
C),
at
atmospheric
pressure
(~
740
torr
local
pressure)
and
at
303
±
1
K
for
arc
light
runs
and
at
301
±
1
K
for
blacklight
experiments.
The
various
characterization
experiments
were
used
to
derive
the
chamber
characterization
parameters
and
evaluate
the
chamber
characterization
model
as
discussed
above.
The
single
organic
­
NOx
experiments
were
carried
out
to
demonstrate
the
utility
of
the
chamber
to
test
the
mechanisms
for
these
compounds,
for
which
data
are
available
in
other
chambers,
and
to
obtain
wellcharacterized
mechanism
evaluation
data
at
lower
NOx
levels
than
previously
available.
The
formaldehyde
+
CO
­
NOx
experiments
were
carried
out
because
they
provided
the
most
chemically
simple
system
that
model
calculations
indicated
was
insensitive
to
chamber
effects,

to
provide
a
test
for
both
the
basic
mechanism
and
the
light
characterization
assignments.
The
aromatic
+
CO
­
NOx
experiments
were
carried
out
because
aromatic
­
NOx
experiments
were
predicted
to
be
very
sensitive
to
the
addition
of
CO,
because
it
enhances
the
effects
of
radicals
formed
in
the
aromatic
system
on
ozone
formation.
The
ambient
surrogate
­
NOx
experiments
were
carried
out
to
test
the
ability
of
the
mechanism
to
simulate
ozone
formation
under
simulated
ambient
conditions
at
various
reactive
organic
gas
(
ROG)
and
NOx
levels.

The
ROG
surrogate
used
in
the
ambient
surrogate
­
NOx
experiments
consisted
of
a
simplified
mixture
designed
to
represent
the
major
classes
of
hydrocarbons
and
aldehydes
measured
in
ambient
urban
atmospheres,
with
one
compound
used
to
represent
each
model
species
used
in
condensed
lumped­
molecule
mechanism.
The
eight
representative
compounds
used
were
n­
butane,
n­
octane,
ethene,
propene,
trans­
2­
butene,
toluene,
m­
xylene,
and
formaldehyde.
(
See
Carter
et
al,
1995c,
for
a
discussion
of
the
derivation
of
this
surrogate).

The
ability
of
the
SAPRC­
99
mechanism
(
Carter,
2000)
to
simulate
the
total
amount
of
NO
oxidized
and
O3
formed
in
the
experiments,
measured
by
([
O3]
final­[
NO]
final)
­
([
O3]
initial­

[
NO]
initial),
or
 ([
O3]­[
NO]),
is
summarized
for
the
various
types
of
experiments
on
Table
3
and
shown
for
the
individual
runs
on
Figure
7.
This
gives
an
indication
of
the
biases
and
run­
to­
run
18
variability
of
the
mechanism
in
simulating
ozone
formation.
In
experiments
with
excess
NO
the
processes
responsible
for
O3
formation
are
manifested
by
consumption
of
NO,
so
simulations
of
 ([
O3]­[
NO])
provides
a
test
of
model
simulations
of
these
processes
even
for
experiments
where
O3
is
not
formed.

Note
that
the
characterization
runs
were
modeled
using
the
same
set
of
characterization
parameters
as
used
when
modeling
the
mechanism
evaluation
runs,
which
are
based
on
averages
of
best
fit
values
for
the
individual
experiments,
and
not
with
the
values
that
were
adjusted
to
fit
the
individual
runs.
Therefore,
the
relatively
large
variability
and
average
model
error
for
the
model
simulations
of
 ([
O3]­[
NO])
in
those
experiments
provides
a
measure
of
the
variability
of
the
chamber
effects
parameters
(
e.
g.,
HONO
offgasing)
to
which
these
experiments
are
sensitive.

The
relatively
low
average
bias
is
expected
because
the
chamber
effects
parameter
values
were
derived
based
on
these
data.

For
the
single
VOC
­
NOx
or
VOC
­
CO
­
NOx
experiments,
the
model
is
able
to
simulate
the
 ([
O3]­[
NO])
to
within
±
25%
or
better
in
most
cases,
which
is
better
than
the
±
~
30%
seen
in
previous
mechanism
evaluations
with
the
older
chamber
data
(
Carter
and
Lurmann,
1990,
1991;

Gery
et
al,
1989,
Carter,
2000).
However,
there
are
indications
of
non­
negligible
biases
in
model
simulations
of
certain
classes
of
experiments.
The
cleaner
conditions
and
the
relatively
lower
magnitude
of
the
chamber
effects
may
make
the
run­
to­
run
scatter
in
the
model
performance
less
than
in
the
simulations
of
the
previous
data,
and
this
tends
to
make
smaller
biases
in
the
model
performance
more
evident.
For
example,
Figure
7
shows
that
the
mechanism
tends
to
underpredict
O3
formation
in
aromatic
­
NOx
experiments
with
added
CO,
even
though
it
has
a
slight
tendency
to
overpredict
O3
in
the
aromatic
­
NOx
experiments
without
added
CO.
This
suggests
problems
with
the
aromatics
mechanisms
that
need
further
investigation
(
Carter,
2004).

The
mechanism
tended
to
have
a
bias
towards
underpredicting
 ([
O3]­[
NO])
in
the
ambient
surrogate
­
NOx
experiments,
though
as
indicated
in
Figure
7
this
underprediction
did
not
occur
for
all
experiments.
The
underprediction
bias
had
very
little
correlation
with
the
initial
ROG
and
NOx
levels
in
the
experiments
but
was
highly
correlated
with
the
initial
ROG/
NOx
ratio.
This
is
shown
in
Figure
8,
which
gives
plots
of
the
 ([
O3]­[
NO])
model
underprediction
19
bias
against
the
initial
ROG/
NOx
ratio
the
experiments.
The
"
error
bars"
show
the
effects
of
varying
the
HONO
offgasing
parameter
over
the
extreme
values
shown
in
Figure
4
for
this
chamber
for
the
303
±
1
K
temperature
range,
which
applicable
to
these
experiments.
It
can
be
seen
that
the
model
has
a
definite
tendency
to
underpredict
 ([
O3]­[
NO])
at
the
low
ROG/
NOx
ratios.
Although
the
HONO
offgasing
parameter
has
a
non­
negligible
effect
on
the
simulations
of
the
experiments
at
the
lowest
and
highest
ROG/
NOx
ratio
(
because
of
sensitivities
to
the
radical
source
in
the
first
case
and
to
the
NOx
source
in
the
second),
the
sensitivity
is
not
sufficient
to
account
to
the
trend
in
the
bias
with
ROG/
NOx.
This
trend
was
not
evident
in
the
previous
mechanism
evaluations,
perhaps
in
part
because
of
the
greater
variabilities
of
the
model
simulations
due
to
greater
chamber
effects
or
characterization
uncertainties,
and
perhaps
in
part
because
this
is
not
as
evident
at
higher
reactant
concentrations.
This
suggests
problems
with
the
mechanism
that
also
needs
further
investigation
(
Carter,
2004).

As
indicated
in
Table
3,
the
initial
evaluation
experiments
included
runs
with
NOx
levels
as
low
as
2­
5
ppb,
which
is
considerably
lower
than
in
experiments
used
previously
for
mechanism
evaluation.
Most
of
the
experiments
used
in
the
previous
SAPRC­
99
mechanism
evaluation
had
NOx
levels
greater
than
50
ppb,
and
even
the
"
low
NOx"
TVA
and
CSIRO
experiments
had
NOx
levels
of
~
20
ppb
or
greater,
except
for
a
few
characterization
runs
(
Carter,

2004,
and
references
therein).
However,
other
than
the
ROG/
NOx
effect
for
the
ambient
surrogate
experiments
discussed
above,
there
is
no
indication
in
any
difference
in
model
performance
in
simulating
the
results
of
these
very
low
NOx
experiments,
compared
to
those
with
the
higher
NOx
levels
more
representative
of
those
used
in
the
previous
evaluation.
This
is
an
important
finding
because
there
has
been
a
concern
about
using
mechanisms
evaluated
at
higher
than
ambient
NOx
levels
for
ambient
simulations
of
remote
areas
or
future
case
attainment
scenarios
(
Dodge,
2000).

For
example,
Figure
9
shows
concentration­
time
plots
for
selected
measured
species
in
ambient
surrogate
­
NOx
experiment
carried
out
at
the
lowest
NOx
levels
in
the
initial
evaluation
runs.
To
indicate
the
sensitivity
of
the
experiments
to
NOx
offgasing
effects,
the
effects
of
varying
the
HONO
offgasing
parameter
from
zero
to
the
maximum
level
consistent
with
the
characterization
experiments
is
also
shown.
It
can
be
seen
that
the
model
using
the
default
20
HONO
offgasing
parameter
value
gives
very
good
fits
to
the
data.
Although
the
O3
simulations
are
somewhat
affected
when
the
HONO
offgasing
rate
is
varied
within
this
somewhat
extreme
range,
the
sensitivity
is
not
so
great
that
the
uncertainty
in
this
parameter
significantly
affects
conclusions
one
can
draw
about
the
ability
of
the
model
to
simulate
this
low
NOx
experiment.

However,
the
sensitivity
would
increase
as
the
NOx
levels
are
reduced,
and
~
2
ppb
NOx
probably
represents
a
reasonable
lower
limit
for
NOx
levels
useful
for
mechanism
evaluation.

Overall,
the
results
of
the
initial
characterization
and
evaluation
indicate
that
this
chamber
can
provide
high
quality
mechanism
evaluation
data
for
experiments
with
NOx
levels
as
low
as
~
2
ppb,
considerably
lower
than
employed
in
previous
experiments.
Chamber
effects
are
not
absent,
but
they
are
as
low
or
lower
than
in
observed
in
any
previous
chambers
used
for
mechanism
evaluation,
in
some
cases
by
an
order
of
magnitude
or
more.
Although
a
larger
number
of
experiments
would
be
required
to
fully
assess
this,
the
results
also
suggest
a
higher
degree
of
precision
in
mechanism
evaluation
than
observed
previously,
making
smaller
biases
in
mechanism
performance
more
evident.
The
initial
dataset
from
this
chamber
indicate
no
significant
problems
with
mechanism
performance
that
are
characteristic
of
low
NOx
conditions
as
such,
but
do
reveal
problems
with
the
mechanisms
for
aromatics
and
the
ambient
ROG
surrogate
(
Carter,
2004).

m­
Xylene­
NOx
SOA
Yield
A
series
of
m­
xylene/
NOx
experiments
photooxidations
were
performed
using
the
blacklights
as
an
irradiation
source.
These
blacklight
experiments
were
carried
with
unhumidified
air
(
dew
point
<
­
40
C),
at
atmospheric
pressure
(~
740
torr
local
pressure)
and
at
at
301
±
1
K.
These
experiments
were
used
to
determine
our
ability
to
perform
SOA
experiments.

The
data
is
analyzed
following
the
original
schemes
outlined
by
Pankow
et
al.
(
1994a,
b)
and
Odum
et
al.
(
1996).
Briefly,
SOA
yield,
Y,
is
defined
as
the
ratio
of
aerosol
(
µ
g
m­
3)
to
hydrocarbon
reacted
(
µ
g
m­
3).



 
+
 
 
=
=

i
org
i
om,
i
om,
i
org
i
i
M
 
 
M
Y
Y
1
(
2)
21
where
 i
is
the
mass­
based
stoichiometric
fraction
of
species
i
formed
from
the
parent
hydrocarbon,
Kom,
i
is
the
gas­
particle
partitioning
coefficient
(
m3
µ
g­
1),
which
is
inversely
proportional
to
the
compound's
vapor
pressure,
and
 
Morg
(
µ
g
m­
3)
is
the
total
mass
concentration
of
organic
material
and
associated
water
present
in
the
aerosol
phase.
The
fraction
of
secondary
organic
material
condensing
into
the
aerosol
phase
is
seen
to
depend
on
the
amount
of
organic
aerosol
mass
present.
The
two­
product
semi­
empirical
model
then
assumes
that
two
surrogate
species
can
be
used
to
estimate
the
SOA
yield:
one
surrogate
product
representing
low
vapor
pressure
compounds
and
one
surrogate
product
representing
high
vapor
pressure
compounds.
(
i=
1,2
in
equation
2)

A
set
of
characterization
runs
was
carried
out
to
demonstrate
the
ability
of
the
chamber
to
perform
SOA
formation
experiments.
M­
xylene
was
chosen
as
the
initial
test
compound.
Four
experiments
with
initial
m­
xylene
and
NO
initial
concentrations
of
75
ppb
and
50
ppb
respectively,
T=
300K,
no
initial
aerosol
present,
and
blacklight
irradiation
source
were
conducted
until
measurable
aerosol
volume
growth
(
corrected
for
wall
loss)
had
ceased
(
approximately
8
hours
irradiation
time,
~
90%
m­
xylene
consumption).
The
experiments
were
conducted
on
both
reactors
with
a
couple
of
months
time
separating
the
first
and
last
experiment.

Average
total
aerosol
production
for
the
four
reactions
was
21.4
±
0.3
µ
g
m­
3.

Additional
m­
xylene/
NOx
experiments
were
performed
with
blacklights
for
comparison
to
previously
published
yield
data.
The
yield
data
are
most
easily
compared
to
recent
m­
xylene
irradiations
at
Caltech
at
comparable
experimental
conditions
(
indoors,
blacklight
source,
similar
temperatures)
(
Cocker
et
al.
2001c),
and
the
results
for
the
various
chambers
are
shown
on
Figure
10.
The
"
Empirical
Fit
through
UCR
Data"
is
the
the
best
fit
two
product
semi­
empirical
fit
yield
curve
for
the
current
dataset
from
this
chamber,
for
which
the
parameters
are
0.075,

0.105,
0.139,
0.010
for
 1,
 2,
 om,
1,
 om,
2,
respectively.
The
overall
agreement
between
this
chamber
and
the
Caltech
chamber
helps
to
verify
the
ability
of
the
new
chamber
to
accurately
simulate
gas­
to­
particle
conversion
processes.
More
details
on
the
current
dataset
for
mxylene
NOx
aerosol
production
can
be
found
in
Song
et
al.
(
2005).
22
Discussion
and
Conclusions
This
chamber
facility
was
designed
to
provide
more
precise
and
comprehensive
mechanism
evaluation
data,
and
at
lower
simulated
pollutant
concentrations,
than
previously
possible.
Although
the
dataset
from
this
chamber
is
still
limited,
the
results
to
date
demonstrate
its
utility
for
providing
valuable
data
for
mechanism
evaluation.
The
major
background
effects
parameters
in
the
chamber
appear
to
be
lower
than
those
observed
in
other
chambers
used
for
mechanism
evaluation,
including
the
TVA
chamber,
which
was
also
designed
for
experiments
at
lower
pollution
levels
(
Simonaitis
and
Bailey,
1995;
Simonaitis
et
al,
1997).

The
lower
background
levels
in
this
chamber
permitted
successful
mechanism
evaluation
experiments
to
be
carried
out
with
NOx
levels
as
low
as
2
ppb.
This
is
at
least
an
order
of
magnitude
lower
than
in
the
mechanism
evaluation
dataset
from
other
chambers
used
for
gasphase
mechanism
evaluation.
In
addition,
we
believe
that
the
lower
background
effects
attainable
in
this
chamber
provided
an
improvement
in
the
precision
of
the
mechanism
evaluation
dataset.

The
results
of
modeling
the
relatively
large
number
of
surrogate
­
NOx
experiments
give
some
information
regarding
this.
Although
the
model
had
systematic
biases
in
simulating
many
of
these
experiments,
as
shown
in
Figure
8,
plots
of
model
biases
against
ROG/
NOx
ratios
had
relatively
little
scatter,
suggesting
fits
to
within
±
10%
could
be
obtained
if
the
current
problem(
s)

with
the
mechanism
can
be
corrected.
This
is
less
than
the
scatter
for
the
fits
to
comparable
experiments
in
other
chambers
(
Carter
and
Lurmann,
1991;
Carter,
2000,
2004).
This
is
important
since
if
the
scatter
in
these
fits
were
on
the
order
of
±
30%,
which
was
observed
mechanism
evaluation
studies
using
other
chamber
data
sets
(
e.
g.,
Carter
and
Lurmann,
1991),

the
ROG/
NOx
dependences
may
not
have
been
statistically
significant,
and
the
mechanism
performance
would
have
been
concluded
to
be
satisfactory.
With
this
more
precise
dataset
the
low
ROG/
NOx
problem
with
the
mechanism
is
evident.

We
believe
that
this
chamber
is
also
well
suited
for
studies
of
secondary
aerosol
formation.
The
good
reproducibility
of
multiple
experiments
and
general
agreement
with
past
work
demonstrates
our
ability
to
accurately
and
precisely
measure
SOA
formation
potentials.
23
Further
work
is
clearly
needed
to
characterize
and
eventually
reduce
or
control
background
aerosol
formation
in
this
chamber,
though
this
appears
to
be
a
problem
with
all
environmental
chambers
used
for
aerosol
studies.
The
relatively
low
chamber
background
effects
and
degree
of
characterization
for
gas­
phase
processes
is
also
a
significant
advantage
in
studies
of
secondary
PM
formation,
since
it
is
the
gas
phase
processes
that
lead
to
the
formation
of
secondary
PM.

The
ability
to
control
temperature
(
and
therefore
humidity)
is
important,
since
data
are
needed
to
systematically
study
gas­
to­
particle
conversion
processes
in
well­
controlled
reactors.

Although
the
experiments
reported
here
were
carried
only
under
dry
conditions
and
at
a
single
temperature,
a
humidification
system
has
been
constructed
and
the
chamber
is
capable
of
controlled
experiments
in
a
wide
temperature
range
of
relevance
to
tropospheric
pollution.

Experiments
to
assess
effects
of
varying
humidity
and
temperature
will
be
discussed
in
subsequent
papers.

Acknowledgements
The
construction
and
initial
characterization
of
this
facility
was
funded
by
the
United
States
Environmental
Protection
Agency
Cooperative
Agreement
No.
CR
827331­
01.
Some
of
the
later
experiments
were
also
funded
through
EPA
Cooperative
Agreement
No.
CR­
830957­

01,
Gail
Tonnesen,
Principal
Investigator,
and
the
lowest
NOx
surrogate
experiments
were
funded
by
California
Air
Resources
Board
Contract
01­
305.
Additional
funding
from
NSF
grant
no.
024111
is
also
acknowledged.
Helpful
discussions
with
Dr.
Basil
Dimitriades
and
Deborah
Luecken,
the
EPA
project
officers,
are
acknowledged.
Assistance
in
the
design
and
construction
of
this
facility
was
provided
by
Mr.
Matthew
Smith.
Dr.
Joseph
Norbeck
provided
valuable
assistance
in
developing
the
necessary
infrastructure
to
house
this
facility.
24
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1994):
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Sulfite
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J.
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Gas/
particle
partitioning
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secondary
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The
atmospheric
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model
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gas/
particle
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the
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"
An
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gas/
aerosol
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secondary
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29
Table
1.
List
of
analytical
and
characterization
instrumentation
Type
Model
or
Description
Species
Sensitivity
Comments
Ozone
Analyzer
Dasibi
Model
1003­
AH.
UV
absorption
analysis.
Monitor
Labs
Chemiluminescence
Ozone
Analyzer
Model
8410
O3
2
ppb
Standard
monitoring
instruments.

NO
1
ppb
NO
­
NOy
Analyzer
Teco
Model
42
C
with
external
converter.
Chemiluminescent
analysis
for
NO,
NOy
by
catalytic
conversion.
NOy
1
ppb
Useful
for
NO
and
initial
NO2
monitoring.
Converter
close­
coupled
to
the
reactors
so
the
"
NOy"
channel
should
include
HNO3
as
well
as
NO2,
PANs,
organic
nitrates,
and
other
species
converted
to
NO
by
the
catalyst.

CO
Analyzer
Dasibi
Model
48C.
Gas
correlation
IR
analysis.
CO
50
ppb
Standard
monitoring
instrument
NO2
0.5
ppb
NO2
data
from
this
instrument
are
considered
to
be
interference­
free.
Tunable
Diode
Laser
Absorption
Spectroscopy
(
TDLAS)
#
1
HNO3
~
1
ppb
HNO3
data
were
not
available
for
all
experiments
discussed
in
this
paper.

HCHO
~
1
ppb
Formaldehyde
data
from
this
instrument
are
considered
to
be
interference­
free.
TDLAS
#
2
TDLAS
analysis
is
based
on
measuring
single
rotational
­
vibrational
lines
in
the
near
to
mid
infrared
using
tunable
laser
diodes
with
very
narrow
line
widths
(
Hastie
et
al.,
1983;
Schiff
et
al.,
1994),
Two
such
instruments
purchased
from
Unisearch
Inc.
and
adapted
for
this
chamber.
Data
transmitted
to
DAC
system
using
RS­
232.
H2O2
~
2
ppb
H2O2
measurements
were
not
made
during
the
experiments
discussed
in
this
paper.

GC­
FID
#
1
HP
5890
Series
II
GC
with
dual
columns,
loop
injectors
and
FID
detectors.
Various
megabore
GC
columns
available.
Controlled
by
computer
interfaced
to
network.
VOCs
~
10
ppbC
Equipped
with:
30
m
x
0.53
mm
GSAlumina
column
used
for
the
analysis
of
light
hydrocarbons
and
30
m
x
0.53
mm
DB­
5
column
used
for
the
analysis
of
C5+
alkanes
and
aromatics.
Loop
injection
suitable
for
low
to
medium
volatility
VOCs
that
are
not
too
"
sticky"
to
pass
through
valves.

VOCs
~
10
ppbC
30
m
x0.53
mm
GSQ
column.
Loop
injection
suitable
for
low
to
medium
volatility
VOCs
that
are
not
too
"
sticky".
Not
used
as
primary
analysis
for
most
of
these
experiments.
GC­
FID
#
2
HP
5890
Series
II
GC
with
dual
columns
and
FID
detectors,
one
with
loop
sampling
and
one
set
up
for
Tenax
cartridge
sampling.
Various
megabore
GC
columns
available.
Controlled
by
computer
interfaced
to
network.
VOCs
1
ppbC
Tenax
cartridge
sampling
can
be
used
for
low
volatility
or
moderately
"
sticky"
VOCs
that
cannot
go
through
GC
valves
but
can
go
through
GC
columns.
Equipped
with
a
30
m
x
0.53
mm
DB­
1701
column.

Luminol
GC
Developed
and
fabricated
at
our
laboratory
based
on
work
of
Gaffney
et
al
(
1998).
Uses
GC
to
separate
NO2
from
PAN
NO2
~
0.5
ppb
NO2
measurements
were
found
to
have
interferences
by
O3
and
perhaps
other
species
and
may
not
be
useful
for
quantitative
mechanism
evaluation.
30
Type
Model
or
Description
Species
Sensitivity
Comments
and
other
compounds
and
Luminol
detection
for
NO2
or
PAN.
Data
transmitted
to
the
DAC
system
using
RS­
232.
PAN
~
0.5
ppb
Reliability
of
measurement
for
PAN
not
fully
evaluated.
Calibration
results
indicate
about
a
30%
uncertainty
in
the
spans.
However,
interferences
are
less
likely
to
be
a
problem
than
for
NO2.

Gas
Calibrator
Model
146C
Thermo
Environmental
Dynamic
Gas
Calibrator
N/
A
N/
A
Used
for
calibration
of
NOx
and
other
analyzers.
Instrument
acquired
early
in
project
and
under
continuous
use.

Data
Acquisition
Sytem
Windows
PC
with
custom
LabView
software,
16
analog
input,
40
I/
O,
16
thermocouple
and
8
RS­
232
channels.
N/
A
N/
A
Used
to
collect
data
from
most
monitoring
instruments
and
control
sampling
solenoids.
In­
house
LabView
software
was
developed
using
software
developed
by
Sonoma
Technology
for
ARB
for
the
Central
California
Air
Quality
Study
as
the
starting
point.

Temperature
sensors
Various
thermocouples,
radiation
shielded
thermocouple
housing
Temperature
~
0.1
oC
Primary
measurement
is
thermocouples
inside
reactor.
Corrections
made
for
radiative
heating
effect
with
arc
light
irradiation.

Humidity
Monitor
General
Eastern
HYGRO­
M1
Dew
Point
Monitor
Humidity
Dew
point
range:
­
40
­
50oC
Dew
point
below
the
performance
range
for
the
unhumidified
experiments
discussed
in
this
paper.

Spectroradiometer
LiCor
LI­
1800
Spectroradiometer
300­
850
nm
Light
Spectrum
Adequate
Resolution
relatively
low
but
adequate
for
its
purpose.
Used
to
obtain
relative
spectrum.
Also
gives
an
absolute
intensity
measurement
on
surface
useful
for
assessing
relative
trends.

Spherical
Irradiance
Sensors
Biospherical
QSL­
2100
PAR
Irradiance
Sensor
or
related
product.
Responds
to
400­
700
nm
light.
Spectral
response
curve
included.
Spherical
Broadband
Light
Intensity
Adequate
Provides
a
measure
of
absolute
intensity
and
light
uniformity
that
is
more
directly
related
to
photolysis
rates
than
light
intensity
on
surface.
Gives
more
precise
measurement
of
light
intensity
trends
than
NO2
actinometry,
but
is
relatively
sensitive
to
small
changes
in
position.

Scanning
Electrical
Mobility
Spectrometer
(
SEMS)
Similar
to
that
described
in
Cocker
et
al.
(
2001a).
See
text
Aerosol
Number
and
Volume
concentration
Adequate
Provides
information
on
size
distribution
of
aerosols
in
the
28­
730
nm
size
range,
which
accounts
for
most
of
the
aerosol
mass
formed
in
our
experiments.
Data
can
be
used
to
assess
effects
of
VOCs
on
secondary
PM
formation.
31
Table
2.
Summary
of
types
of
characterization
experiments
and
types
of
chamber
effects
parameters
relevant
to
gas­
phase
mechanism
evaluation
derived
from
these
experiments.

Run
Type
No.
Runs
Sensitive
Parameters
Comments
Ozone
Dark
Decay
4
O3
wall
loss
rate
The
loss
of
O3
in
the
dark
is
attributed
entirely
to
a
unimolecular
wall
loss
process.

CO
­
Air
8
NOx
offgasing
Insensitive
to
radical
source
parameters
but
O3
formation
is
very
sensitive
to
NOx
offgasing
rates.
Formaldehyde
data
can
also
be
used
to
derive
formaldehyde
offgasing
rates.

CO
­
HCHO
­
air
2
NOx
offgasing.
Insensitive
to
radical
source
parameters
but
O3
formation
is
very
sensitive
to
NOx
offgasing
rates.
Also
can
be
used
to
obtain
formaldehyde
photolysis
rates
CO
­
NOx
6
Initial
HONO,
Radical
source
O3
formation
and
NO
oxidation
rates
are
very
sensitive
to
radical
source
but
not
sensitive
to
NOx
offgasing
parameters.
Formaldehyde
data
can
also
be
used
to
derive
formaldehyde
offgasing
rates.

n­
Butane
­
NOx
1
Initial
HONO,
Radical
source
O3
formation
and
NO
oxidation
rates
are
very
sensitive
to
radical
source
but
not
sensitive
to
NOx
offgasing
parameters.

Pure
Air
6+
NOx
offgasing,
Background
VOCs
Used
primarily
to
screen
for
background
VOC
effects
with
the
NOx
offgasing
and
chamber
radical
source
parameter
set
at
values
that
fit
the
other
types
of
characterization
experiments.
32
Table
3.
Summary
of
initial
experiments
carried
out
in
the
chamber.

Average
 (
O3­
NO)
Model
Fits
[
c]
Run
Type
[
a]
Runs
[
b]
NOx
(
ppb)
CO
(
ppm)
VOC
(
ppb
except
as
noted)
Bias
Error
Pure
Air
6
0
0
0
See
note
[
d]

Other
Characterization
32
0­
202
0­
168
0­
490
­
3%
28%

HCHO
 
NOx
2
8
­
23
35­
50
­
23%
23%

HCHO
­
CO
­
NOx
2
16
­
21
14­
76
39­
49
­
10%
10%

Ethene
 
NOx
2
10
­
25
617­
650
­
15%
15%

Propene
 
NOx
2
5
­
24
42­
52
16%
16%

Toluene
 
NOx
3
5
­
24
61­
152
11%
11%

m­
Xylene
­
NOx
(
arc
light)
1
5
18
6%
6%

m­
Xylene
­
NOx
(
blacklight)
18
17­
100
25­
215
[
e]

Toluene
­
CO
­
NOx
5
4
­
27
24­
50
55­
165
­
16%
17%

m­
Xylene
 
CO
­
NOx
1
6
­
6
47
18
­
21%
21%

Surrogate
­
NOx
61
[
f]
2
­
315
0.2
­
4.2
[
g]
­
10%
13%

[
a]
Arc
light
used
unless
indicated
otherwise
[
b]
Each
reactor
irradiation
is
counted
as
a
separate
run,
so
two
runs
are
done
at
once.

[
c]
Error
and
bias
for
model
predictions
of
 ([
O3]­[
NO])
using
the
SAPRC­
99
mechanism.
Bias
is
(
calculated
­
experimental)
/
calculated.
Error
is
the
absolute
value
of
the
bias.

[
d]
The
average
6­
hour
O3
yields
for
the
pure
air
runs
with
blacklights
and
standard
conditions
are
4
±
2
ppb
experimental
and
6
±
2
ppb
calculated.
[
e]
Not
used
for
gas­
phase
mechanism
evaluation.
See
discussion
of
SOA
yield
experiments.

[
f]
Includes
experiments
carried
out
for
subsequent
projects
[
g]
ppmC
33
20
ft.
20
ft.
20
ft.
This
volume
kept
clear
to
maintain
light
uniformity
Temperature
controlled
room
flushed
with
purified
air
and
with
reflective
material
on
all
inner
surfaces
Dual
Teflon
Reactors
Two
air
Handlers
are
located
in
the
corners
on
each
side
of
the
light
(
not
shown).

Gas
sample
lines
to
laboratory
below
Access
Door
200
KW
Arc
Light
2
Banks
of
Blacklights
SEMS
(
PM)
Instrument
Floor
Frame
Movable
top
frame
allows
reactors
to
collapse
under
pressure
control
Mixing
System
Under
floor
of
reactors
Figure
1.
Schematic
of
the
environmental
chamber
reactors
and
enclosure.

0.0
0.2
0.4
0.6
0.8
0.300
0.350
0.400
0.450
0.500
0.550
0.600
Wavelength
(
microns)
UCR
EPA
Blacklights
Solar
Z=
0
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.290
0.300
0.310
0.320
Relative
Intensity
(
Normalized
to
give
same
NO2
photolysis
rate)

Figure
2.
Spectrum
of
the
argon
arc
light
source
used
in
the
chamber.
Blacklight
and
representative
solar
spectra,
with
relative
intensities
normalized
to
give
the
same
NO2
photolysis
rate.
34
0
1
2
3
4
5
6
7
50
75
100
125
150
175
EPA
Run
Number
NOx
or
Radical
Input
(
ppt/
min)

Radical
Input
(
Side
A)

Radical
input
(
Side
B)

NOx
Input
(
Side
A)

NOx
Input
(
Side
B)

Used
in
Model
(
Side
A)

Used
in
Model
(
Side
B)

Figure
3.
Plots
of
NOx
or
radical
input
rates
necessary
for
model
simulations
to
predict
the
experimental
data
against
experimental
run
number
(
i.
e.,
against
the
order
the
experiment
was
carried
out).
35
1
10
100
1000
290
300
310
320
Average
Temperature
(
K)
HONO
Offgasing
Paramenter,
RN
(
ppt)

Previous
UCR
Indoor
Previous
UCR
Outdoor
Previous
UCR
Default
Model
UNC
Outdoor
Model
TVA
Indoor
(
NOx
offgasing)

UCR
EPA
(
first
series)

UCR
EPA
(
later
series)

SAPHIR
HONO
offgasing
Figure
4.
Plots
of
the
HONO
offgasing
parameter,
RN
(
ratios
of
the
HONO
offgasing
rates
the
NO2
photolysis
rates)
derived
from
modeling
characterization
runs
for
various
chambers.
Data
shown
are
for
unhumidified
experiments
except
for
the
UNC
outdoor
and
TVA
chambers.

0
2
4
6
8
10
12
75
125
175
225
275
325
Run
No.
Particle
Decay
(/
day)

Side
A
Side
B
Avg
A
Avg
B
Reactors
Changed
Figure
5.
Plots
of
particle
loss
rates
against
time
for
experiments
from
February
2003
through
June
of
2004
36
Side
A
Side
B
Maximum
PM
Number
0.0
0.5
1.0
1.5
2.0
150
200
250
300
350
Run
Number
5
Hour
PM
Volume
(
ug/
m3)
Pure
Air
Propene
­
NOx
First
Run
in
New
Reactor
150
200
250
300
350
Run
Number
CO
­
Air,
CO
­
NOx
Blacklight
0
5000
10000
15000
20000
150
200
250
300
350
Run
Number
Maximum
PM
Number
150
200
250
300
350
Run
Number
PM
Volume
at
5
Hours
of
Irradiation
Figure
6.
Plots
of
5­
Hour
PM
volume
and
maximum
PM
number
data
in
PM
background
characterization
experiments
in
the
reactors
installed
before
run
169.
37
All
Characterization
HCHO
­
NOx
HCHO
­
CO
­
NOx
Ethene
­
NOx
Propene
­
NOx
Toluene
­
NOx
Toluene
­
CO
­
NOx
m­
Xylene
­
NOx
m­
Xylene
­
CO
­
NOx
Surrogate
­
NOx
­
75%
­
50%
­
25%
0%
25%
50%
75%

(
Calculated
­
Experimental)
/
Experimental
Single
Run
Average
Figure
7.
Fits
of
experimental
O3
formed
and
NO
oxidized,
 ([
O3]­[
NO]),
measurements
to
SAPRC­
99
model
calculations
for
the
initial
chamber
and
mechanism
evaluation
experiments.
38
­
50%
­
40%
­
30%
­
20%
­
10%
0%
10%
20%
30%
40%
50%

1
10
100
1000
ROG
/
NOx
(
ppmC
/
ppmN)
(
Experimental
­
Calculated)
/
Experimental
 ([
O3]­[
NO])

(
Experimental
­
Calculated)
/
Experimental
 ([
O3]­[
NO])

Figure
8.
Plots
of
the
tendency
of
the
SAPRC­
99
mechanism
for
underpredicting
ozone
formed
and
NO
oxidized,
 ([
O3]­[
NO]),
against
the
initial
ROG/
NOx
ratio
in
the
surrogate
­
NOx
experiments.
Error
bars
show
the
effect
of
varying
the
HONO
offgasing
chamber
effects
parameter
within
its
uncertainty.
39
Concentration
(
ppm)
vs
Time
(
minutes)
O3
0.00
0.01
0.02
0.03
0.04
0
120
240
360
NO
0.000
0.001
0.002
0
120
240
360
NO2
0.0000
0.0005
0.0010
0.0015
0
120
240
360
m­
Xylene
0.000
0.002
0.004
0.006
0
120
240
360
PAN
0.0000
0.0002
0.0004
0.0006
0
120
240
360
NOy
­
HNO3
0.000
0.001
0.002
0.003
0.004
0
120
240
360
Experimental
Standard
Model
No
HONO
Offgasing
Maximum
HONO
Offgasing
Figure
9.
Concentration­
time
plots
of
selected
compounds
in
the
lowest
NOx
ambient
ROG
­
NOx
surrogate
experiment
in
the
initial
evaluation
experiments
(
NOx
 
1
ppb,
ROG
 
300
ppbC.
40
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
0.160
0
50
100
150
200
250
300
Mo(
µ
g/
m3)
Yield
Empirical
fit
through
UCR
data
Caltech
data
for
dry
m­
xylene
experiments
UCR
data
for
dry
m­
xylene
Figure
10.
Comparison
of
yield
data
obtained
for
m­
xylene/
NOx
system
with
blacklight
irradiation.
Solid
squares
represent
data
obtained
in
this
reactor
(
UCR);
open
diamonds
are
for
dry
experiments
conducted
in
the
Caltech
reactor
(
Cocker
et
al.,
2001b);
the
solid
line
represents
the
best­
fit
two­
product
model
for
the
current
UCR
data
set.
