First-time direct proof of chemical reactions in particulates

Paul Scherrer Institute

André Prévôt (right) und Urs Baltensperger at the newly developed device that analyses molecules in particulate matter. Credit: Paul Scherrer Institute/Mahir Dzambegovic

André Prévôt (right) und Urs Baltensperger at the newly developed device that analyses molecules in particulate matter. Credit: Paul Scherrer Institute/Mahir Dzambegovic

Researchers at the Paul Scherrer Institute PSI have developed a new method to analyse particulate matter more precisely than ever before. With its help, they disproved an established doctrine: that molecules in aerosols undergo no further chemical transformations because they are enclosed in other suspended particulate matter. In the smog chamber at PSI, they analysed chemical compounds directly in aerosols and observed how molecules dissociated and thus released, for example, gaseous formic acid into the atmosphere. These findings will help to improve the understanding of global processes involved in cloud formation and air pollution and to refine the corresponding models. The results of this investigation are published today in the journal Science Advances.

Anyone who takes a walk through a coniferous forest and enjoys the tangy, refreshing air is inhaling α-pinene. This is one of the volatile organic compounds in the oils of conifer trees, and it also occurs in eucalyptus and rosemary. The smell triggers pleasant feelings in most people. Less pleasant is that the compound changes in the atmosphere, under the influence of radicals, into other compounds, so-called highly oxidised organic molecules. Some of these are reactive, to some extent harmful substances. They have only recently come under scrutiny by atmospheric researchers, and their role, for example in cloud formation, is not yet understood.

These highly oxidized organic molecules are less volatile than the starting substance α-pinene and therefore condense easily. Together with dust particles and other solid and liquid substances in the air, they form what we call particulate matter or aerosols.

“Up to now it was thought that such molecules are protected from further transformations once they have landed in particulate matter,” says Andre Prévôt of the Laboratory of Atmospheric Chemistry at PSI. “It was believed that they then would not change any more, but would simply spread out over the atmosphere and eventually rain down.”

This widespread opinion does not correspond to reality, however, as Prévôt and his fellow researchers at PSI showed: “The reactions continue, even in the particulate matter.” The molecules remain reactive and either react with each other to form larger particles or disassociate, thereby releasing for example formic acid. This common compound is found not only in ants and stinging nettles, but also in the atmosphere, where it is an important indicator of air pollution.

The PSI researchers’ observations should help to improve simulation models, such as those for cloud formation and air pollution. The models simulate what happens in the atmosphere to predict, for example, how a reduction in certain emissions will affect air quality.

From the aerosol into the measuring device

For the first time, PSI researchers analysed chemical compounds directly in particulate matter under atmospheric conditions. For this they used the PSI smog chamber, in which processes in the atmosphere can be simulated. The researchers injected a droplet of α-pinene into the chamber and caused the compound to react with ozone. Over a period of 15 hours, they observed which chemical compounds formed from α-pinene and which disappeared again afterwards.

This was made possible by a new analytic device for atmospheric measurements that the researchers developed in cooperation with the company Tofwerk in Thun, Switzerland: a so-called EESI-TOF (extractive electrospray ionisation time-of-flight mass spectrometer). “It also detects larger molecules directly in the aerosol,” explains atmospheric chemist Urs Baltensperger. “Previous measurement methods, on the other hand, chop up the molecules into smaller fragments at high temperatures.” The new device ionises without fragmentation. “We can record each molecule separately.”

Tofwerk has now brought the device to market with the help of PSI, so that other atmospheric researchers can also benefit from the new method.

Measurements in Zurich

The new analytic method can be used not only in the laboratory, but also directly on site.

During the winter of 2018/19 and the summer of 2019, PSI researchers used it to investigate aerosols in the air in Zurich.

As it turned out, a good third of Zurich’s particulate matter in summer consists solely of reaction products of α-pinene and similar molecules. In winter, however, emissions from wood-burning systems and their reaction products come to the fore.

The researchers have planned further measurement campaigns in China and India. There they want to analyse which molecules form in the air of a city with more than a million inhabitants.

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The research results are being published on 13 March 2020 in the journal Science Advances.

Text: Paul Scherrer Institute / Brigitte Osterath

About PSI

The Paul Scherrer Institute PSI develops, builds and operates large, complex research facilities and makes them available to the national and international research community. The institute’s own key research priorities are in the fields of matter and materials, energy and environment and human health. PSI is committed to the training of future generations. Therefore about one quarter of our staff are post-docs, post-graduates or apprentices. Altogether PSI employs 2100 people, thus being the largest research institute in Switzerland. The annual budget amounts to approximately CHF 407 million. PSI is part of the ETH Domain, with the other members being the two Swiss Federal Institutes of Technology, ETH Zurich and EPFL Lausanne, as well as Eawag (Swiss Federal Institute of Aquatic Science and Technology), Empa (Swiss Federal Laboratories for Materials Science and Technology) and WSL (Swiss Federal Institute for Forest, Snow and Landscape Research).

Original publication

On the fate of oxygenated organic molecules in atmospheric aerosol particles
V. Pospisilova, F. D. Lopez-Hilfiker, D. M. Bell, I. El Haddad, C. Mohr, W. Huang, L. Heikkinen,
M. Xiao, J. Dommen, A. S. H. Prévôt, U. Baltensperger, J. G. Slowik
Science Advances, 13 March 2020 (online)
DOI: 10.1126/sciadv.aax8922

Further information

An extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) for online measurement of atmospheric aerosol particles
F. D. Lopez-Hilfiker, V. Pospisilova, W. Huang, M. Kalberer, C. Mohr, G. Stefenelli, J. A. Thornton, U. Baltensperger, A. S. H. Prévôt, J. G. Slowik
Atmospheric Measurement Techniques, 11 September 2019 (online)
DOI: 10.5194/amt-12-4867-2019

Organic aerosol source apportionment in Zurich using an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) – Part 1: Biogenic influences and day-night chemistry in summer
G. Stefenelli, V. Pospisilova, F. D. Lopez-Hilfiker, K. R. Daellenbach, C. Hüglin, Y. Tong, U. Baltensperger, A. S. H. Prévôt, J. G. Slowik
Atmospheric Chemistry and Physics, 10 December 2019 (online)
DOI: 10.5194/acp-19-14825-2019

Organic aerosol source apportionment in Zurich using an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF-MS) – Part 2: Biomass burning influences in winter
L. Qi, M. Chen, G. Stefenelli, V. Pospisilova, Y. Tong, A. Bertrand, C. Hueglin, X. Ge, U. Baltensperger, A. S. H. Prévôt, J. G. Slowik
Atmospheric Chemistry and Physics, 20 June 2019 (online)
DOI: 10.5194/acp-19-8037-2019

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17 thoughts on “First-time direct proof of chemical reactions in particulates

  1. This widespread opinion does not correspond to reality, however

    Oh dear, there goes another “doctrine” of settled science.

    Now we can acknowledge that we sweet FA about cloud formation and precipitation maybe it’s a good time to admit with don’t know enough about basic climate controlling processes to make stupid extrapolations and projections about how climate will respond in 100y time to a particular change in “forcings”.

    • Greg, you beat me to the quote from the article “This widespread opinion does not correspond to reality, however…”

      I agree with your comment under the assumption that you meant to say the climate research community knows sweet FA about cloud formation and precipitation.

      Regards,
      Bob

  2. Gosh.

    Does that mean that the “40,000” people killed by pm2.5s in the UK might actually still be fit & well?

    No wonder they couldn’t name one.

  3. As an analytical chemist in my early career, I envy these folk and what they can do with this clever, advanced equipment. We used to dream about techniques like this, now they are real. May they be used by genuine scientists. Geoff S

  4. “Don’t drink the water and don’t breathe the air”, was Tom Lehrer’s advice in, I think, “Pollution, Pollution” — and that was 60 years ago!!

    • wear a gas mask and a veil…
      Then you can breathe
      ‘long as you don’t inhale!

      Still relevant after all these years.
      But please, not 60 years ago yet. It was 1965.

    • Los Angeles – in the 1970’s.

      I shot an arrow into the air – and it stuck there…..

  5. I have long speculated over the annual volume of air passing through car engines, jet aircraft, etc. and whether the huge mass involved together with pressure and temperature excursions as well as the particulates, would over decades change the atmosphere in some fundamental way.

    Perhaps this technique may shed some light.

    • At least for cars and trucks with catalyst and trap technologies, the air coming out of the vehicle is cleaner than the air going in in terms of PM. This is true for areas such as SoCal. This comment came from a researcher at UC Riverside who runs their emissions test program. They have to ultra-filter the inlet air in order to meet exhaust out emissions standards. If not, the ambient air is above the standard and the engine will fail the test. This is an example of over-regulation of emissions by the government to no useful purpose. But they still want lower emissions from vehicles which only hurts fuel economy and cost. I believe this is a back-handed way to force EV’s on everyone. Regulate what you don’t like out of existence.
      But with crude at near historic lows (corrected for inflation, crude is at $4.20/bbl in 1970 dollars), why would we want to transition away from a cheap, abundant resource.

  6. My comment below deals with this study but also goes beyond to other related work being done at PSI.

    It’s understandable to simplify models so that elementary reactions, etc. can be studied, but these guys really should include CO2 in their simulated air when they are studying secondary aerosols, particularly when these involve ammonium sulfates. Some of the reactions they study involve reactants in ppb and even ppt concentrations, CO2 is present at several orders of magnitude higher and can readily participate in acid/base chemistry.

    In their CLOUD experiments, they did not even include argon, which has a very different ionization energy than N2 and O2. They might at least do some baseline experiments including argon before questioning Svensmark’s ethics. I’ve personally spoken to Urs, and in my opinion it is clear that the PSI undermines work and results that do not fit the IPCC narrative.

  7. At least for cars and trucks with catalyst and trap technologies, the air coming out of the vehicle is cleaner than the air going in in terms of PM. This is true for areas such as SoCal. This comment came from a researcher at UC Riverside who runs their emissions test program. They have to ultra-filter the inlet air in order to meet exhaust out emissions standards. If not, the ambient air is above the standard and the engine will fail the test. This is an example of over-regulation of emissions by the government to no useful purpose. But they still want lower emissions from vehicles which only hurts fuel economy and cost. I believe this is a back-handed way to force EV’s on everyone. Regulate what you don’t like out of existence.
    But with crude at near historic lows (corrected for inflation, crude is at $4.20/bbl in 1970 dollars), why would we want to transition away from a cheap, abundant resource.

  8. Surface chemistry is a branch of chemistry in its own right because conditions are different at surfaces. At the molecular level, the molecules at the surface are not surrounded entirely by identical molecules as would be the case in the bulk. Instead they are in contact with molecules of a different chemistry and maybe even a different phase of matter. The chemical bonding and other forces at these interfaces are therefore different compared with in the bulk and they tend to be much more reactive. This reactivity tends to increase with the decreasing size of the particles due to large increase in the surface areas involved.
    Surface chemistry is at the heart of finely divided materials used as catalysts or the special properties of nanoparticles. It is my interest in surface chemistry that has convinced me of the chemical reactivity opportunities in the atmosphere where dispersions, emulsions, solids, liquids and gases are irradiated by visible, UV and IR radiation together with a variety of high velocity ions from the solar wind and cosmic radiation.
    These materials are not present in high concentrations but in terms of numbers of particles they must be huge. The potential for interactions is high. Add to all of that the electrostatic attraction or repulsion of charged ions and free radicals in the effects of the solar and earth magnetic fields.
    It is perhaps not surprising that there is not much known about the micro-scale chemistry of the atmosphere.

  9. The report reads like somebody with very little knowledge of heterogeneous phase chemistry is writing something to deliberately confuse someone with no knowledge of chemistry.
    Totally unreadable.

  10. I always wondered why Christmas tree lots smelled so great but pine scent air fresheners always smelled like soap.

  11. There has been work done on aerosols at CERN, the particle accelerator facility in europe. I’m surprised this article doesn’t even mention that work.
    As clouds are acknowledged to be the biggest greenhouse gas (even by the IPCC) I would hope to find more articles on WUWT, sadly not…_

    CERN aerosol research

  12. The EESI-TOF should be used to revisit the ozone-fluorocarbon connection to see if such a connection actually exists — or not.

  13. “they disproved an established doctrine: that molecules in aerosols undergo no further chemical transformations because they are enclosed in other suspended particulate matter. ”

    That doctrine is about as established as phlogiston.

    The doctrine among virtually everyone is the exact opposite. Congrats on proving was was already generally accepted as true from multiple experiments over the course of decades.

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