Experimental Challenges at EUPHORE: The NO Denuder Solution

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Experimental Challenges at
EUPHORE: The NO
x

Denuder
Solution



Shar Samy

April 9, 2007

Presentation Outline


European Photoreactor (EUPHORE)


Overall description


Technical Specifications



Atmospheric Transformation of Diesel Emissions



-
Objectives




-
Experimental challenges, in regards to NO
x



-
Attempted solutions, and results


The chambers in Valencia, Spain.


Technical Specifications


half
-
spherical Teflon (FEP) bag with a volume of about 200 m3



fluorine
-
ethene
-
propene (FEP) foil

Specifications: 0.13mm thickness, transmission >80% (280
-
640nm)



chamber is self stabilizing against wind distortions when operated with an excess
pressure of 100
-
200 Pa



internal framework made of epoxy
-
resin tubes based on a half
-
spherical network
construction keeps the foil in shape in the absence of excess internal pressure



refrigeration system integrated in the chamber floor, which compensates for chamber
air heating by solar radiation



Ports for input of the reactants and sampling lines for the different analytical
instruments are located on the chamber floor











Instrument

Compounds /
Parameter

Detection limit

Sampling Method

Analysis Type

FTIR Magna 550

VOCs

10 ppb

In
-
situ White mirror system (553m
optical path)

On
-
line

GC
-
FID/PID

Fison 8000

VOCs,

Carbonyls

20 ppb

10 ppb

5 ml sampling loop

On
-
line

Fison TGA GC/FID

VOCs

1 ppb

Cryogenic enrichment

On
-
line

HPLC

UV/VIS

Carbonyl Compounds

1
-
2 ppb by
DNPH

DNPH cartridges

30 l air samples

Off
-
line

HPLC
-
Fluorescence

H
2
O
2
, Hydroperoxides

< 1 ppb

Double stripping coil

Off
-
line

NO
x

Monitor

ECO Physics

NO, NO
2

< 1ppb

Teflon line

On
-
line

NO
x

Monitor Labs.

NO, NO
y

1 ppb

Teflon line

On

line

CO Monitor TE48C

CO

20 ppb

Teflon line

On line

Ozone Monitor

O
3

1 ppb

Teflon line

On
-
line

Spectral Radiometer

Solar Flux

------

Inside the reactor, 50 cm above the
ground

6 min average

Temperature

T

------

Below fan in the shadow

1 min average

Pressure

P

------

Teflon line

1 min average

Dew Point TS
-
2

Humidity

-
50ºC

Teflon line

1 min average

Chamber B, Analytical Instrumentation

The overall objective of this study is
to investigate photochemical
transformations of diesel emissions
in the atmosphere.




The specific aims are:


(1) to characterize the gas
-

and particle
-

phase products of atmospheric
transformations of diesel emissions under the influence of sunlight,
ozone, hydroxyl radicals, and nitrate radicals (in the dark).


(2) to explore the changes in biological activity of diesel exhaust before
and after the atmospheric transformations take place.

Why is all this work necessary ?

We all understand part of the
complexity



Once released into the atmosphere,
primary diesel emissions (or any other
direct emissions) are subject to dispersion
and transport .


Various physical and chemical processes,
determine their ultimate environmental
fate.


The role of the atmosphere may be
compared in some ways with that of a
giant chemical reactor in which materials
of varying reactivity are mixed together,
subjected to chemical and/or physical
processes, and finally removed.

The Photoreactor Model

WHY?


better understanding of the health risks of
exposure of general populations to
secondary pollutants derived from
atmospheric transformation of diesel
emissions.


geographic extent of the influence of these
emissions (coupled with future sampling
campaigns), “Transformation Profile”

Experimental Challenges


The modern 1.8 L, Lynx V277 90PS Stage 3,
Delphi Fuel System, Fixed Geometry Turbo
Diesel Engine emits very high levels of NO +
NO
2

= NO
x






~400ppm !



This engine is used in the Ford Focus and
Transit Connect automobiles.

Experimental Matrix

(three campaigns combined)

Run Description

Purpose

# of Runs

Run Description

Purpose

# of
R
u
ns

Diesel Exhaust
Dark (D
-
1)

Determine changes in
exhaust composition
due to aging in
chamber.

8

Diesel Exhaust
Only,

Light (L
-
1)

Examine effects of
photolysis reactions
on exhaust
composition, low NOx

4

N
2
O
5

+ Diesel
Exhaust,

Dark (D
-
2)

Investigate effects of NO
3
on
diesel exhaust
composition. N
2
O
5
decomposes to form
NO
2
and NO
3
.

8

HCHO + Diesel
Exhaust,
Light(L
-
2)

Study reactions of OH
radicals (from HCHO
photolysis) with diesel
exhaust under low
NOx

6

O
3
+Diesel
Exhaust,

Dark (D
-
3)

Study reactions of ozone
with diesel exhaust in
the dark, under low
NOx

3

Diesel Exhaust +
Toluene,
Light(L
-
3)

Diesel exhaust as seed
aerosol during the
oxidation of toluene.
Low NOx conditions

4

Objective


Investigation of atmospheric
transformation processes under realistic
ambient conditions?




In order to carry out light exposures and
O
3
dark exposures in low NO
x

conditions,
a NO
x

denuder was developed for this
work.

What is a NO
x
Diffusion Denuder ?


A device that removes gas phase NO +
NO
2

= NO
x
from an air or effluent stream,
while allowing other gases and suspended
particles to flow through unperturbed
(ideal).


Isolation and Enrichment of
Analytes, “Denudation”


A dynamic method based on passing of an
air (effluent) stream through a suitably built
container in which certain components of
the analyzed air sample are retained
(enriched).


Selective adsorption of NOx is achieved
by way of diffusion or permeation.

Assuming movement of molecules
and/or particles is achieved by two
main forces:


A force vectored in accordance with the
direction of the gas stream, resulting from
the force flow of gas


A force perpendicular to the longitudinal
axis of the denuder (and its walls),
resulting from the radial diffusion

From: Kloskowski, A. et al,

Critical Rev. Analytical Chem. ,
2002.



Solid particles are relatively massive and travel
straight through the denuder (high momentum)



“The gas molecules are moving all over the
place, like toddlers; eventually they hit the wall
and stick. The trick is to calculate the airflow and
the length of the tube
--

to make it short enough
so the particles stay airborne but long enough
for the gas to get trapped."
Lara Gundel, 1999

Diffusion Coefficients




NO2, D=10 cm2/min




Particles 1um D=1.64x10
-
5
cm2/min

Some basic principles of operation

-
flow of gas must be stable and laminar


-
analyte releasing technique cannot influence sample composition


-

the device should be operated under steady



state conditions of pressure and temperature


-

temperature and viscosity distributions must be uniform within the stream of gas


-

longitudinal diffusion of the analyzed gaseous components should be negligible


as compared with the linear velocity of gas flow


-
sorption material should be a good sink for the analytes in question


-

adsorbate should not undergo any secondary transformations within the denuder,
that is, neither new compounds should appear, or those already present disappear.


What is Laminar Flow?

R
e
=
velocity*diameter*density
viscosity


Re < 2000, indicates laminar flow

Reynolds number

A non
-
dimensional number, which is the ratio of inertial
forces to viscous forces

Commonly used to identify different flow regimes

(turbulent vs. laminar)

Cobalt Oxide


An efficient absorption material for the
capture of nitrogen oxides (NO, NO2, and
HNO3) from exhaust streams



Coatings can be regenerated by heating
them in a flushing air or oxygen flow to
about 400

C, resulting in the release of
absorbed NOx, thus allowing the material
to be used again

Campaign #1

January, 2005


A small denuder was initially constructed (for the winter, 2005 campaign)
using cobalt oxide coatings on the inner walls of small cylindrical stainless
steel tubes, but found some objections to this design approach because of
imperfect adhesion of the coating to the metal and the NOx removal
efficiency



A 2
-
min introduction of diesel exhaust to the chamber produced
approximately 30 μg/m3 of diesel PM and nearly 1 ppm of NOx (30% of this
as NO2)



Because of the high NOx concentrations in the chamber, it was not possible
to carry out certain exposure scenarios. For example, dark ozone
exposures


Initial Denuder

FTIR Data Chamber
0
100
200
300
400
500
600
9:00
10:00
11:00
12:00
13:00
14:00
15:00
16:00
17:00
18:00
19:00
20:00
21:00
Time, hh:mm
NO, NO
2
and NO
y
Concentration, ppb
NOy ML
NO
NO API
NO ECO
NO2
NO2 API
NO2 ECO
12-Jan-2005
B
Exhaust diesel (15% aromatics) with NOx denuder
Very little removal efficiency, immediate blow through of NOx is
apparent

Campaign #2

May, 2005


Ceramic (e.g., “cordierite”) honeycomb
denuder configuration



Pros and Cons


Maximized surface area, which the
honeycomb configuration provides is an
attractive feature


Stability of the cobalt oxide coating on the
honeycomb sections resulted in frictional
and turbulent material loss (flaking)


Impaction of particles (d=0.48cm), and
lack of removal efficiency (and storage
capacity) of NOx


NO mixing ratio for honeycomb
denuder experimental setup.


FTIR NO, May 2005
0
100
200
300
400
500
600
700
6
7
8
9
10
11
12
13
14
15
16
17
18
19
GMT Time (hh)
Concentration (ppb)
nitric oxide
Improvements Needed


Work was carried out in fall/winter 2005
-
2006 to improve the design of the
denuder. A design goal of 90% NO
x

absorption in concentrations ranging as
high as 400ppm (typical for a modern
diesel) was established at the onset of the
work.


A Cobalt Oxide coated NOx absorptive
material (“GROG”, an industry term, a
firebrick prerequisite material ) was
developed


A miniature multi
-
channel cylindrical
denuder was utilized for testing

Cobalt Oxide Coated GROG


GROG

is composed of Silca (~50%), Alumina (~%40), Iron Oxide (~2%),
Titania (~2%), and several other earth metals (sodium, potassium, etc…)

Pre
-
coated, sifted
GROG

Post
-
coated,
GROG

GROG
coating procedure ?
Make it up !

4
-
channel cylindrical denuder


Each channel is 39cm long (four total), with a channel diameter of 2.5cm



An additional 15cm pre
-
chamber was constructed to establish laminar flow
of effluent, prior to the channel entrances



Packing of absorbent material on the


outside of the main interior channels


allows for efficient transport and


replacement of the packing material


(or regeneration )



Once effluent flow is established,
gaseous diffusion through the mesh
apertures (~1mm) allows for efficient
removal of NOx

Channel
pathways
were left
completely
open (line
-
of
-
site), to
reduce
particulate
loss due to
impaction


Mini
-
denuder setup

NO Denuder Experiment 10-26-05
y = 0.0166x
2
- 0.8711x + 17.519
0
20
40
60
80
100
120
140
160
180
0
20
40
60
80
100
120
140
Elapsed Time (Minutes)
FTIR Reading, PPM
NO removal efficiency remained >90% for
approximately 80 minutes, utilizing a 400ppm source

10.7% total NO breakthrough for the entire 121
minutes

Several other experiments were
carried out:


To evaluate the impacts of temperature on
the NOx storage equilibruim (i.e. storage
capacity)


Variations of chemistry in production of the
absorbent (e.g. Barium/Cobalt)


Regeneration of the coated
GROG


Optimal depth of the
CO
-
GROG,
and the
impacts on removal/storage capacity

Temperature Variance Exp.

Temp. Ramp NO Desorb Experiment
0
50
100
150
200
250
0
15
30
45
60
75
90
105
120
Time (Minutes)
FTIR Response (PPM)
50C

100C

125oC

150C

175C

The Depth Chamber Experiment

Campaign #3

May/June 2006

The Scale up of the mini
-
denuder experiments !

Due to lack of time and resources, no
experimentation was performed on the new denuder
prior to the field campaign

The New Denuder

Some Specs.


66” length (packed section) x 14.5” (internal
diameter) was constructed in the spring of 2006



internal 57
-
channel configuration, with
perforated tubing



The cylindrical channels have a 1” O.D., with an
appropriate external spacing (between
channels) for the optimal NOx absorbent
performance (established via depth
experiments).

Shipping to Spain

Assembly

Run type

NOx
Denud
er
usage

Engine
-
out
NOx(ppm)

Time of DE
injecti
on
(min)

Chamber
NOx
(ppm)

DPM
(μg/m
3
)

Median
diamet
er
(nm)

Mean
diamet
er
(nm)

DE, dark

No

430

6

1.7

33

62

71

DE, dark

No

410

10

2.6

60

61

69

DE, dark

Yes

390

20

0.009

30

75

84

DE, light

Yes

415

27

0.050

54

88

100

DE, light+OH

Yes

400

15+10+10*

0.025

37

87

96

DE, light+OH

Yes

410

17+7+6*

0.025

30

91

100

DE, light

Yes

371

20+10**

0.024

42

94

103

DE, light
+toluene

Yes

363

20+10**

0.034

39

93

102

DE, dark

No

-

10

2.5

66

65

74

Some initial results

Another example of denudation
-
based sampling method.


Capture of semi
-
volatile organic
compounds (SVOC) on a glass annular
denuder

XAD Denuder

Gundel et al., Atmos. Environ., 1995

Gundel and Lane, 1999


Denuder

Gas phase and particles with
adsorbed SVOC enter an annular
diffusion denuder


Filter

Solid
Adsorbent

Gas phase molecules diffuse to, are
trapped on, and retained by the
denuder walls

Because the particles have much
greater momentum than gas phase
molecules, they pass through the
denuder and are trapped on a filter

Some of the particle
-
associated SVOC
leave the particles and are trapped on the
solid adsorbent

Chemical extraction

and analysis of the

denuder yields the

The sum on the filter

and the solid adsorbent

yields the

Annular Diffusion Denuder

Doug Lane, Organic Speciation Workshop, Las Vegas, NV, 2004


MICROSCOPIC CREVICES IN RESIN BEADS TRAP GAS
MOLECULES WHEN THEY HIT THE WALLS OF THE
INTEGRATED ORGANIC VAPOR/ PARTICLE SAMPLER.


From: Preuss, P.
Berkeley Lab: Science Beat
, Sept 1, 1999.

Operational Definitions of SVOC and PM
-

Associated OC


Filter
-
Adsorbent (FA)

A

F

A

F

D

Denuder
-
Filter
-
Adsorbent (DFA)

A

E

Electrostatic precipitator
(EA)

Filter
-
Filter
-
Adsorbent (FFA)

F
1

F

A

Lara Gundel, Organic Speciation Workshop, Las Vegas, NV, 2004

Problems with Denuders


XAD
-
4 denuders are difficult to use and labor
intensive


Denuders that adsorb gases can act as
chromatographic columns


Particles that are less than 50 nm behave more like
gases than particles in a denuder


Longer denuders are more effective gas traps, but
increased transit time results in larger particle losses
and a greater chance for particle
-
associated
molecules to leave the particle while it passes through
the denuder


Learning to balance the trade
-
offs is a necessary skill
for interpreting and successfully using denuder
technology












From: “Challenges in Speciation of Aerosols”, by B. Zielinska

Particle Size and number distribution for
dark diesel exhaust aging in EUPHORE
,
2006



Particle Size distribution Chamber B

0

50000

100000

150000

200000

250000

0

50

100

150

200

250

300

Dp (nm)

dN/dLogDp (#/cm

3

)

11:40:59

13:20:57

18:15:50

13
-
Jun
-
2006

D
-
1 run in June 2006

Particle Size and # distribution for dark
diesel exhaust aging with NOx denuder
,
2006

Particle Size distribution Chamber B

0

10000

20000

30000

40000

50000

60000

70000

0

50

100

150

200

250

300

Dp (nm)

dN/dLogDp (#/cm

3

)

14:27:40

16:07:38

18:07:35

31
-
May
-
06

SMPS data displays a D
-
1 experiment in May 2006, with the NOx denuder connected

Discussion


The initial mean and median particle diameter
increased to ~90nm, with the denuder in
-
line



The required increase in diesel exhaust injection
time to the chamber when utilizing the denuder
may explain this shift (i.e. more time for the
small particles to coagulate, or residence time).



50nm particles begin to act like gases (i.e.
diffusivity coefficient)

Additional Analyses


Polyaromatic Hydrocarbons (PAH)


Nitrated
-
PAH (NPAH)


Polar compounds


Alkanes, Hopanes, Steranes (fuel
combustion markers)

Thank Our Sponsor

The Health Effect Institute

www.healtheffects.org

The Health Effects Institute

"A Partnership of the U.S. Environmental Protection Agency and Industry"


Contact me for further information:



Email:
ssamy@dri.edu



Phone: 674
-
7095



Future Projects, Questions, Comments.