Smog chamber @ Paul Scherrer Institut

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Table of Contents Technical description Instrumentation Research interests at the smog chamber Experiments Highlights Collaborations Downloads (Password required) References Contacts Links

1. Technical description

The chamber is a 27-m³ (3×3×3 m) flexible bag made of 125 mm (5 mil) DuPont™ Teflon^® fluorocarbon film (FEP, type 500A, Foiltec GmbH, Germany). The bag is suspended in a temperature controlled wooden enclosure having dimension 4×5×4 m (L×W×H). The walls and ceiling of the enclosure are covered with reflective aluminium foil to maximize the light intensity and increase light scatter or diffusion. The aluminium foil has greater than 80% reflection for spectra greater than 300 nm. The chamber temperature is controlled by two cooling units allowing for temperature stabilization of ±1°C within the range of 15 to 30 °C. Three manifolds (inlet and outlet) made of stainless steel and Teflon^® allow for easy installation of additional inputs and sampling lines.

Four xenon arc lamps (4 kW rated power, 1.55x10⁵ lumens each, XBO^® 4000 W/HS, OSRAM) are used to simulate the solar light spectrum and to mimic natural photochemistry. One lamp is placed at each corner of the housing. Indirect light was chosen over direct light to increase light homogeneity, thus decreasing possible “hot spots” of photochemical activity. The lamps are directed alongside the bag walls. The light is filtered with borosilicate glass plates to reduce the high actinic UV below the wavelength of 300 nm. A NO₂ photolysis rate of  J_NO2 = 0.12 min^-1 is obtained.

Purified air is supplied by an AADCO (737-250 series, AADCO Instruments, Inc., USA) pure air generation system. Gaseous components (NO, NO₂, gaseous organic compounds) are supplied to the smog chamber through a mass-flow controlled system (model 5850S, control unit Model 0154, Brooks Instruments) and Teflon^® lines. An ozone generator is provided by irradiation of pure air in quartz tubes with UV lamps. The generator can operate with 1 to 3 lamps and various flow rates, providing ozone of ppb to ppm concentrations in the chamber.Liquid parent HC is evaporated in a 500 ml glass sampling bulb. The sampling bulb is wrapped in a silicon heater (80°C) and flushed with 10-15 l min^-1 of AADCO pure air. In addition, transport lines to the chamber downstream of the glass bulb are wrapped in silicon heaters (80°C) to prevent high boiling point compounds from condensing on transport line walls.For humidification ultrapure water is heated and mixed with pure air to flush it into the chamber within heated tubes.

A particle generation system is available for seed particle experiments. Seed particles may be generated using a TSI 3076 type nebulizer.

Figure 1: Smog chamber enclosure. Rectangular tubes on top belong to ventilation system. Grey cubes at half height are housings of xenon arc lamps.

Figure 2: Inside view of smog chamber: Suspended bag; inlet lines; walls covered with reflective aluminium. Some of the aerosol instrumentation is inside the chamber to keep it at the same temperature as the bag.

2. Instrumentation

The smog chamber is equipped with a fixed set of instruments which are regularly operated. Additionally, there are many special state of the art instruments of our own (marked red) or in close collaboration (marked green; M. Kalberer, Department of Chemistry and Applied Biosciences, ETH Zurich) which are used for measurements at the chamber.

3. Research interests at the smog chamber

The smog chamber is used to investigate the formation and composition of atmospheric aerosols produced from gaseous precursors. In a recent paper (Kalberer et al., 2004) we presented for the first time experimental evidence of oligomer formation and growth over time in secondary organic aerosols. We also showed that oligomers can comprise a large fraction of the SOA and that they are formed from small carbonyls and/or organic acids.

Smog chamber experiments are usually carried out at fairly high concentrations. We aim at operating our facility also at low atmospherically relevant precursor concentrations. Projects are underway to develop and use new instrumentation to measure the physical and chemical properties of aerosols. We have collaboration with a research group to investigate biological effects of aerosols.

4. Experiments

A typical experiment includes the following steps:

1. Humidification of chamber to desired humidity
2. Input of Nitrogen oxide gases
3. Input of volatile organic compound
4. This mixture is let to mix for about 30 min before lights are turned on

Figure 3a shows the time profile of the aerosol formation (number concentration) of an experiment with initial mixing ratios of 600 ppb 1,3,5-Trimethylbenzene (TMB), 300 ppb propene, 160 ppb NO, 160 ppb NO₂ and a humidity of 50%. For an animation press Figure 3b. After 30 min first aerosols with a diameter of 7 nm are observed which rapidly increase in number and size to about x0’000 particles/cm3 and 100-150 nm. In Figure 4 the consumption of TMB and the formation of Ozone (O₃) and methylglyoxal (m/z 73) as measured by PTR-MS is presented.

Figure 3a: Typical time-resolved number-weighted size distribution from an irradiated 1,3,5-TMB, propene, NO_x experiment.

Figure 3b: Animation of time development of aerosol number concentration. Click onto the graph.

Figure 4: Time evolution of mixing ratios of ozone (O3, NO, CO, 1,3,5-TMB and methylglyoxal (m/z 73).

5. Highlights

Oligomerization in aerosol particles

Our measurements with the V-TDMA and LDI-MS offered strong evidence, that in SOA formed from TMB and a-pinene oligomerization occurs [Kalberer et al. 2004, Paulsen.et al. 2005]. This means that small oxygenated products formed in the photooxidation of these compounds react in the particles and form macromolecules. This process is illustrated in Figures 5 and 6. Figure 5 depicts mass spectra taken by LDI-MS at 2.5 and 6.5 hours after starting irradiation. It is well seen that molecules with higher masses are formed after 2.5 hours which finally yield a nice regular mass spectral pattern between m/z 400-600 Da. Macromolecules up to a m/z 900 could be observed. The V-TDMA measurements reveal the remaining volume of a particle after heating it to temperatures of 100, 150 or 200 °C. As is seen in Figure 6 the remaining volume increases from 45% after 4.5 hours to 90% after 12 hours. Similar trends are observed for 150 and 200 °C. Up to 30% of the aerosol volume does not evaporate anymore after 15 hours even at 150°C. This can be explained by the formation of less volatile macromolecules as observed by the appearance of high mass signals by LDI-MS.  

Figure 5: Measurement of oligomers in SOA from TMB measured with LDI-MS after 2.5 and 6.5 hours.

Figure 6: Time evolution of volume fraction remaining for TMB experiment measured with a VTDMA.

6. Collaboration

EUROCHAMP (http://www.eurochamp.org/)
Our smog chamber is partner of the “Infrastructure” program EUROCHAMP (Integration of European Simulation Chambers for Investigating Atmospheric Processes) where the main goal is to provide researchers access to state-of-the-art smog chamber facilities in Europe

ACCENT EU6 “Network of Excellence” program (Atmospheric Composition Change: A European Network). http://www.accent-network.org/
ACCENT fosters communication and collaboration within the whole European scientific community in the field of atmospheric change research. This program also supports access to infrastructure and data bases.

7. Downloads (Password required)

Smogchamber data can be downloaded by authorized users from the download area. Authorized users may obtain their access information and password from either Peter Barmet or Josef Dommen.

8. References

Alfarra, M.R., D. Paulsen, M. Gysel, A.A. Garforth, J. Dommen, A.S.H. Prévôt, D.R. Worsnop, U. Baltensperger, and H. Coe, A mass spectrometric study of secondary organic aerosols formed from the photooxidation of anthropogenic and biogenic precursors in a reaction chamber, Environ. Sci. Technol., submitted, 2004.

Fisseha, R., J. Dommen, M. Sax, D. Paulsen, M. Kalberer, R. Maurer, F. Höfler, and U. Baltensperger, Identification of organic acids in secondary organic aerosol and the corresponding gas phase from chamber experiments. Anal. Chem., 76(22), 6535-6540, 2004.

Kalberer, M., D. Paulsen, M. Sax, M. Steinbacher, J. Dommen, A.S.H. Prevot, R. Fisseha, E. Weingartner, V. Frankevich, R. Zenobi, U. Baltensperger, Identification of polymers as major components of atmospheric organic aerosols, Science, 303, 1659-1662, 2004.

Paulsen, D., J. Dommen, M. Kalberer, A.S.H. Prevot, R. Richter, M. Sax, M. Steinbacher, E. Weingartner, U. Baltensperger, Secondary organic aerosol formation by irradiation of 1,3,5 trimethylbenzene-NO_x-H₂O in a new reaction chamber for atmospheric chemistry and physics, Environ. Sci. Technol., accepted, 2005.

Paulsen, D., E. Weingartner, R.M. Alfarra, and U. Baltensperger, Volatility measurements of photochemically- and nebulizer- generated organic particles, J. Aerosol. Sci., submitted, 2004.

9. Contacts

Josef Dommen
Laboratory of Atmospheric Chemistry
Paul Scherrer Institut
5232 Villigen PSI
Switzerland

Email: josef.dommen@psi.ch

Urs Baltensperger
Laboratory of Atmospheric Chemistry
Paul Scherrer Institut
5232 Villigen PSI
Switzerland

Email: urs.baltensperger@psi.ch

10. Links

Paul Scherrer Institut:  http://www.psi.ch/

Laboratory of Atmospheric Chemistry:  http://www.psi.ch/lac

last updated: 2008-11-18