Detection and Speciation of Gas-Phase Atmospheric Peroxy and Criegee Radicals

Project Information

EPHEMERAL

Grant agreement ID: 884532

DOI

10.3030/884532

EC signature date 20 August 2020

Start date 1 April 2021

End date 31 March 2027

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 3 419 744,00

EU contribution

€ 3 419 744,00

Coordinated by

KUNGLIGA TEKNISKA HOEGSKOLAN
Sweden

Periodic Reporting for period 3 - EPHEMERAL (Detection and Speciation of Gas-Phase Atmospheric Peroxy and Criegee Radicals)

Reporting period: 2024-04-01 to 2025-09-30

Summary of the context and overall objectives of the project

Organic radicals, such as peroxy radicals (RO2) and Criegee intermediates, are key compounds in the chemistry of many natural and artificial systems, such as Earth’s atmosphere. In Earth’s atmosphere they drive the oxidation of pollutants, greenhouse gases and other compounds, thus control the atmosphere’s ability to clean itself or “oxidizing capacity”. This oxidizing capacity maintains the composition of the atmosphere constant and is an indicator of its “health”, for instance in climate change or air pollution events. RO2 radical reactions are also important in the atmosphere because they produce Highly Oxygenated Molecules (HOMs) and, ultimately, aerosol particles. But these organic radicals are difficult to observe individually, which considerably limits the understanding of their chemistry. Despite decades of studying their reactions in laboratory and attempting to observe them in the atmosphere, modeled and observed atmospheric radical concentrations are still differing today. These discrepancies indicate some important remaining gaps in the knowledge of the reactions of these radicals, which, in turn, limits the accuracy in describing today’s atmospheric chemistry and predicting its evolution with climate change.

The objective of project EPHEMERAL is to substantially improve the understanding of the atmospheric chemistry of these organic radicals by
a) developing the first technique allowing for the observation of individual organic radicals in the atmosphere (WP2), in particular of small alkyl peroxy radicals such as CH3O2, which are the most important and,
b) using this technique in laboratory to investigate some reactions of these radicals not studied previously, but which have the potential of reconciling observations and models (WP1 + WP3).

The expected results of EPHEMERAL would thus be well beyond the state of the art by

1) providing the scientific community with the first tool to monitor and quantify individual organic radicals in the atmosphere (and laboratory), thus giving access to chemical information, which was inaccessible until now. This level of information is essential to understand the chemistry of these radicals and to constrain atmospheric chemical models,
2) providing the first experimental information on unexplored reactions of these radicals, thereby improving the fundamental understanding of their chemistry in the atmosphere.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work performed and main results achieved so far in project EPHEMERAL are:

In WP2
The development of a technique to detect individual organic radicals in the atmosphere is about half-way into reaching its objective. Two state-of-the-art proton transfer time-of-flight mass spectrometers (PTR-tof-MS, “FUSION”, Ionicon Analytik, Gmbh) were purchased and optimized. These instruments could not initially detect the radicals and a first series of optimization was performed to improve their performances. At the time of this report both instruments can detect RO2 radicals, including CH3O2 and other small alkyl RO2 that are important in the atmosphere. While their detection sensitivities are currently a factor 10 to 50 below the performances necessary to detect the radicals in the atmosphere, they are the first time-of-flight mass spectrometers able to detect these radicals, which already allows for innovative investigations in laboratory, such as in WP3. In addition, a PERCA/ECHAMP instrument was built in WP2, which is being used to quantify the concentrations of RO2 observed by the MS instruments (“calibrations”).

In WP1
Several classes of reactions of RO2, never or hardly studied previously, have already been studied. Their reactions with unsaturated compounds (alkenes) were studied for the first time at room temperature, and the first experimental rate coefficients for H-shift and cyclisation reactions for unsatured RO2, contributing to the formation of HOMS and aerosols, were determined. Studies of the effects of water vapor on the reactions of RO2 are about to begin.

In WP3
The uptake and reactions of RO2 with various surfaces were studied for the first time. The reactivity of these radicals towards some surfaces, in particular metals, was found to be very high and in competition with their gas-phase chemistry. This suggests that some current knowledge of the reactivity of these radicals, based on laboratory setups where metal surfaces are important, might be inaccurate.

In conclusion, while the major breakthrough set in the project’s objectives have not been reached yet, the progress made so far is about half way towards these objectives. Several major achievements have been made, both in term of instrument/technique development and in investigating radical reactions in laboratory, which should soon open some new perspectives on the reactivity of these radicals in the atmosphere.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In this first part of the project, the results that can be considered as beyond the state of the art are:

- the optimization of two PTR-tof-MS instruments into the first instruments able to detect individual RO2, including small alkyl RO2 such as CH3O2, with significant sensitivity,
- the first exploration of the uptake and reactions of RO2 on surfaces, evidencing the importance of these reactions. The results of this study have direct implications on the materials to be chosen in the project to sample and analyze these radicals. They also question the current understanding of the reactivity of these radicals, mostly established from laboratory set-ups where surfaces are important.

The next steps and expected results of the project are further improvements of the detection performances of the instruments towards organic radical and their application to their detection in the atmosphere. In addition to RO2, the detection of Criegee Intermediates (CI) with these instruments will be tested and optimized.
Other unexplored reactions of RO2 will be studied, in particular some that could account for the recycling of RO2 into OH in the absence of NO, subject of intense investigations in the last 15 years, and which might resolve the discrepancies between atmospheric observations and models.

Detection of CH3O2 with the PTr-tof-MS