Experimental Challenges at EUPHORE: The NO x Denuder Solution

1. Experimental Challenges at EUPHORE: The NOx Denuder Solution Shar Samy April 9, 2007

2. 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

3. The chambers in Valencia, Spain.

8. 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

9. Chamber B, Analytical Instrumentation

11. 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.

12. Why is all this work necessary ?

13. 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.

14. 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.

15. 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”

16. 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.

17. Experimental Matrix(three campaigns combined)

18. 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.

19. 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).

20. 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.

21. 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

22. From: Kloskowski, A. et al, Critical Rev. Analytical Chem. , 2002.

23. 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

24. Diffusion Coefficients • NO2, D=10 cm2/min • Particles 1um D=1.64x10-5cm2/min

25. 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.

26. What is Laminar Flow?

27. 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

28. 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

29. 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

30. Initial Denuder

31. Very little removal efficiency, immediate blow through of NOx is apparent

32. Campaign #2May, 2005 • Ceramic (e.g., “cordierite”) honeycomb denuder configuration

33. 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

34. NO mixing ratio for honeycomb denuder experimental setup.

35. 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.

36. 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

37. 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 !

38. 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

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

40. Mini-denuder setup

41. NO removal efficiency remained >90% for approximately 80 minutes, utilizing a 400ppm source 10.7% total NO breakthrough for the entire 121 minutes

42. 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

43. Temperature Variance Exp. 125oC 100C 175C 150C 50C

44. The Depth Chamber Experiment

45. 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

46. The New Denuder

47. 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).

48. Shipping to Spain

49. Assembly

50. Some initial results