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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

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Presentation Transcript
presentation outline
Presentation Outline
  • European Photoreactor (EUPHORE)
    • Overall description
    • Technical Specifications
  • Atmospheric Transformation of Diesel Emissions
    • -Objectives
    • -Experimental challenges, in regards to NOx
    • -Attempted solutions, and results
technical specifications
Technical Specifications
  • half-spherical Teflon (FEP) bag with a volume of about 200 m3
  • fluorine-ethene-propene (FEP) foilSpecifications: 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
slide11

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.

we all understand part of the complexity
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.
slide14

The Photoreactor Model

  • 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.
slide15
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
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 + NO2 = NOx

~400ppm !

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

objective
Objective
  • Investigation of atmospheric transformation processes under realistic ambient conditions?
  • In order to carry out light exposures and O3 dark exposures in low NOx conditions, a NOx denuder was developed for this work.
what is a no x diffusion denuder
What is a NOx Diffusion Denuder ?
  • A device that removes gas phase NO + NO2 = NOx from an air or effluent stream, while allowing other gases and suspended particles to flow through unperturbed (ideal).
isolation and enrichment of analytes denudation
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
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
slide23
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
Diffusion Coefficients
  • NO2, D=10 cm2/min
  • Particles 1um D=1.64x10-5cm2/min
some basic principles of operation
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.

slide27

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)

Re = velocity*diameter*density viscosity

Re < 2000, indicates laminar flow

cobalt oxide
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
Campaign #1January, 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
campaign 2 may 2005
Campaign #2May, 2005
  • Ceramic (e.g., “cordierite”) honeycomb denuder configuration
pros and cons
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
improvements needed
Improvements Needed
  • Work was carried out in fall/winter 2005-2006 to improve the design of the denuder. A design goal of 90% NOx absorption in concentrations ranging as high as 400ppm (typical for a modern diesel) was established at the onset of the work.
slide36
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
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
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
slide39

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

slide41

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
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
Temperature Variance Exp.

125oC

100C

175C

150C

50C

campaign 3 may june 2006
Campaign #3May/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

some specs
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).
another example of denudation based sampling method
Another example of denudation-based sampling method.
  • Capture of semi-volatile organic compounds (SVOC) on a glass annular denuder
xad denuder
XAD Denuder

Gundel et al., Atmos. Environ., 1995

Gundel and Lane, 1999

slide53

Annular Diffusion Denuder

Chemical extraction

and analysis of the

denuder yields the

Gas Phase

The sum on the filter

and the solid adsorbent

yields the

Particle Phase

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

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

Denuder

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

Filter

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

Solid Adsorbent

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

slide54
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.

slide55

Filter-Adsorbent (FA)

F

A

Filter-Filter-Adsorbent (FFA)

F1

F

A

D

E

Denuder-Filter-Adsorbent (DFA)

F

A

A

Electrostatic precipitator (EA)

Operational Definitions of SVOC and PM - Associated OC

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

problems with denuders
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

13-Jun-2006

Particle Size distribution Chamber B

250000

11:40:59

13:20:57

18:15:50

200000

)

3

150000

dN/dLogDp (#/cm

100000

50000

0

Dp (nm)

0

50

100

150

200

250

300

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

D-1 run in June 2006

particle size and distribution for dark diesel exhaust aging with nox denuder 2006

31-May-06

Particle Size distribution Chamber B

70000

14:27:40

16:07:38

60000

18:07:35

50000

)

3

40000

dN/dLogDp (#/cm

30000

20000

10000

0

0

50

100

150

200

250

300

Dp (nm)

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

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

discussion
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
Additional Analyses
  • Polyaromatic Hydrocarbons (PAH)
  • Nitrated-PAH (NPAH)
  • Polar compounds
  • Alkanes, Hopanes, Steranes (fuel combustion markers)
thank our sponsor
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
Contact me for further information:
  • Email: ssamy@dri.edu
  • Phone: 674-7095
  • Future Projects, Questions, Comments.