Two press release on this this week, both below

From the University of Manchester

Researchers discover particle which could ‘cool the planet’

In a breakthrough paper published in Science, researchers from The University of Manchester, The University of Bristol and Sandia National Laboratories report the potentially revolutionary effects of Criegee biradicals.

These invisible chemical intermediates are powerful oxidisers of pollutants such as nitrogen dioxide and sulfur dioxide, produced by combustion, and can naturally clean up the atmosphere.

Although these chemical intermediates were hypothesised in the 1950s, it is only now that they have been detected. Scientists now believe that, with further research, these species could play a major role in off-setting climate change.

The detection of the Criegee biradical and measurement of how fast it reacts was made possible by a unique apparatus, designed by Sandia researchers, that uses light from a third-generation synchrotron facility, at the Lawrence Berkeley National Laboratory’s Advanced Light Source.

The intense, tunable light from the synchrotron allowed researchers to discern the formation and removal of different isomeric species – molecules that contain the same atoms but arranged in different combinations.

The researchers found that the Criegee biradicals react more rapidly than first thought and will accelerate the formation of sulphate and nitrate in the atmosphere. These compounds will lead to aerosol formation and ultimately to cloud formation with the potential to cool the planet.

The formation of Criegee biradicals was first postulated by Rudolf Criegee in the 1950s. However, despite their importance, it has not been possible to directly study these important species in the laboratory.

In the last 100 years, Earth’s average surface temperature increased by about 0.8 °C with about two thirds of the increase occurring over just the last three decades.

Most countries have agreed that drastic cuts in greenhouse gas emissions are required, and that future global warming should be limited to below 2.0 °C (3.6 °F).

Dr Carl Percival, Reader in Atmospheric Chemistry at The University of Manchester and one of the authors of the paper, believes there could be significant research possibilities arising from the discovery of the Criegee biradicals.

He said: “Criegee radicals have been impossible to measure until this work carried out at the Advanced Light Source. We have been able to quantify how fast Criegee radicals react for the first time.

“Our results will have a significant impact on our understanding of the oxidising capacity of the atmosphere and have wide ranging implications for pollution and climate change.

“The main source of these Criegee biradicals does not depend on sunlight and so these processes take place throughout the day and night.”

Professor Dudley Shallcross, Professor in Atmospheric Chemistry at The University of Bristol, added: “A significant ingredient required for the production of these Criegee biradicals comes from chemicals released quite naturally by plants, so natural ecosystems could be playing a significant role in off-setting warming.’

From DOE/Sandia National Laboratories

Sandia, UK partners publish groundbreaking work on Criegee intermediates in Science magazine

		IMAGE:Sandia combustion researchers Craig Taatjes and David Osborn discuss data found from the detection and measurement of Criegee intermediate reactions. The apparatus seen on the left was used to make…Click here for more information.

LIVERMORE, Calif. — In a breakthrough paper published in this week’s issue of Science magazine, researchers from Sandia’s Combustion Research Facility, the University of Manchester and Bristol University report direct measurements of reactions of a gas-phase Criegee intermediate using photoionization mass spectrometry. (visit www.youtube.com/SandiaLabs to see a short video of Sandia combustion chemists discussing the research.)

Criegee intermediates – carbonyl oxides – are implicated in autoignition chemistry and are pivotal atmospheric reactants, but only indirect knowledge of their reaction kinetics had previously been available. The article, titled Direct Kinetic Measurements of Criegee Intermediate (CH2OO) Formed by Reaction of CH2I with O2, reports the first direct kinetics measurements made of reactions of any Criegee species, in this case formaldehyde oxide (CH2OO). These measurements determine rate coefficients with key species, such as sulfur dioxide (SO2) and nitrogen dioxide (NO2), and provide new insight into the reactivity of these transient molecules.

The detection and measurement of the Criegee intermediate reactions was made possible by a unique apparatus, designed by Sandia researchers, that uses light from a third-generation synchrotron user facility, Lawrence Berkeley National Laboratory’s Advanced Light Source, to investigate chemical reactions that are critical in hydrocarbon oxidation. The intense tunable light from the synchrotron allows researchers to discern the formation and removal of different isomeric species – molecules that contain the same atoms but arranged in different combinations.

In the present case, CH2OO can be distinguished from its more stable isomer, formic acid (HCOOH), because of their differing thresholds for photoionization. The Manchester and Bristol researchers recognized that this apparatus could elucidate not only combustion reactions but also important tropospheric oxidation processes, such as ozonolysis.

Ozonolysis, or the cleavage of carbon-carbon double bonds through reaction with ozone, is a reaction that plays a key role in a number of fields, including synthetic chemistry and tropospheric removal of unsaturated hydrocarbons. In the 1950s, Rudolf Criegee proposed that ozonolysis of alkenes occurs via the carbonyl oxide biradicals, now called Criegee intermediates. Criegee intermediates also have been calculated to be markers of critical chain-branching steps in hydrocarbon autoignition chemistry.

However, until 2008 no gas-phase Criegee intermediate had been observed, and rate coefficients derived from indirect measurements spanned orders of magnitude.

In the Science publication, Sandia researchers reported a new means of producing gas-phase Criegee intermediates and used this method to prepare enough CH2OO to measure its reactions with water, SO2, nitric oxide (NO), and NO2. The ability to reliably produce Criegee intermediates will facilitate studies of their role in ignition and other oxidation systems.

In particular, the present measurements show that the reactions of CH2OO with SO2 and NO2 are far more rapid than previously thought. Moreover, the Bristol and Manchester investigators demonstrated that these kinetics results imply a much greater role of carbonyl oxides in tropospheric sulfate and nitrate chemistry than models had assumed, a conclusion that will substantially impact existing atmospheric chemistry mechanisms. For example, SO2 oxidation is the source of sulfate species that nucleate atmospheric aerosols. Because the oxidation of SO2 by Criegee intermediate is much faster than modelers assumed, Criegee reactions may be a major tropospheric sulfate source, changing predictions of tropospheric aerosol formation.

This capability breakthrough was funded by the Office of Basic Energy Sciences (BES) within the Office of Science in the U.S. Department of Energy, and conducted using the Advanced Light Source, a scientific user facility supported by BES.

Sandia National Laboratories is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin company, for the U.S. Department of Energy’s National Nuclear Security Administration. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness.