Are ice phase electrochemical processes in deep convective clouds inducing new particle formation in the upper troposphere?

• Applicant: Dr. Alexander Theis
• Subject Area: Atmospheric Science
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 505864778

It is now recognized that climate change is one of the most pressing problems for our societies for the upcoming decades. In this context, reliable climate projections are of enormous political and socio-economical relevance. However, such accurate predictions are currently hindered by a still limited understanding of key atmospheric parameters such as the atmospheric chemical composition, aerosol loading, cirrus clouds and circulation feedbacks in the upper troposphere/lower stratosphere (UTLS) region, i.e. at altitudes from 10 to 20 km. In particular, our knowledge about the key, climate relevant, constituents e.g. water vapor, ice particles and aerosols is quite incomplete. Very recently, intense new particle formation (NPF) events have been observed in the UTLS, where ice formation and deep convection are predominant. It seems that the region above tropospheric clouds is a favorable venue for the formation of new particles. The underlying mechanism is, however, only very qualitatively described. Those NPF events are are possibly associated with the high-altitude formation of condensable vapors, and not just with the uplifting of polluted air masses containing those. NPF requires a source of atmospheric oxidants reducing the volatility of precursor gases to form nanometer-sized particles via gas-to-particle conversion. This oxidant source should be strong enough to compete with the condensational sinks induced by the preexisting particles.We suggest that the formation of ice particles via the freezing of supercooled liquid water followed by water condensation on them are sources of H2O2 or HOx radicals in the UTLS driving NPF. The freezing of aqueous solutions has been documented to produce electric fields (the so-called Workman-Reynolds effect). Similarly, it has been shown recently that the preferred chemical bond orientation at the air/water interface induces an electric interfacial potential. Such localized electric fields may induce electrochemical processes in or on the ice particles producing H2O2 or HOx and contributing significantly to the oxidative capacity of the atmosphere, thereby affecting new particle and cloud formation and, finally the earth’s radiative budget and climate. This hypothesis is supported by some very recent up-to-date measurements and reports .This project aims at unraveling and quantifying those processes for the first time.

• DFG Programme: Research Grants
• International Connection: France
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Cooperation Partner: Privatdozent Dr. Christian George