Multiphase Chemical Kinetics

Trace gases that are emitted in the atmosphere contain elements in relatively low oxidation states. Their oxidation in the O₂-rich atmosphere is crucial in determining their impact on atmospheric composition. This is brought about by chemical reactions across the gas phase, deliquescent aerosols, and cloud droplets. Chemical kinetics in and across these different media is our key to advance the understanding and prediction of oxidants and aerosol precursors in the troposphere.

Tropospheric oxidants

• Volatile organic compounds and tropospheric ozone
• Influence of transition metal ions on radical cycling
• Heterogeneous formation of nitrous acid

Aerosol precursors

• Pathways to formation of organic acids
• Formation of polyols and oligomers
• Highly oxygenated molecules from auto-oxidation of organics
• Formation of carbonyl sulfide from biogenic organic sulfur
• Sulfur and nitrogen chemistry leading to extreme haze
• Formation and ageing of aromatics contributing to brown carbon

Activities

1. Oxidation mechanisms development with the open community box model CAABA/MECCA.
2. Development of a 0D-base model within MESSy comprising multiphase chemical kinetics, aerosol microphysics, photolysis etc.
3. ECHAM5/MESSy for atmospheric chemistry (EMAC), the only global model explicitly simulating multiphase chemical kinetics
4. Design and interpretation of SAPHIR experiments.
5. Mechanism evaluation against chamber experiments.
6. Collect experimental kinetic data and compare simulation results to field campaign measurements.

Atmospheric Chemistry across the scales

The assessment and the exploration of the role of atmospheric chemistry in the Earth system rely on efficient use of supercomputers for ever increasing detail and resolution of simulations. In this context we push the frontiers of knowledge along with the technical frontiers for atmospheric chemistry models within the HGF-ESM project. Our developments are targeted to efficiently use upcoming exascale supercomputing technologies for our simulations. Specifically, we

• are engaged in the porting of the MESSy submodel MECCA to GPUs with CUDA C, CUDA libraries and OpenACC
• implement and test matrix-free integrators for large and stiff ODE systems with higher order time-stepping schemes.
• develop a prototype “MESSy dwarf”, i.e., a framework to run and tests each MESSy submodel or a combination of MESSy submodels outside of the MESSy legacy models in a carefully refined (test) setup.
• take actively part in the development of ICON/MESSy which probably will replace ECHAM5/MESSy in the future.

These developments can be considered as IEK-8’s contribution to the Helmholtz Association project PL-ExaESM.

Pollution and weather

Weather determines the physical conditions under which pollution and pollutant emissions develop. Vice versa, gaseous and particulate pollutants affect local radiative forcing and cloud formation. Moreover, the short-term responses of terrestrial vegetation to weather extremes involve significant changes of trace gases emission and removal. Specifically, we investigate:

• The impact of evapo-transpiration on pollutants during droughts and heat waves
• The role of temperature and humidity in the photochemical production of ozone during weather extremes
• The links between humidity and atmospheric brown carbon and the related regional warming

Atmospheric composition and climate

The chemistry of the atmosphere mediates diverse couplings between the biosphere and climate. We investigate the short-term feedbacks which may counteract or dampen perturbations of the physical state of the atmosphere. We are interested in building mechanistic representations of how volatile organic compounds may affect aerosol and cloud formation and thus the radiative balance of the atmosphere. In particular we focus on the significance of:

• Non-methane hydrocarbons from terrestrial vegetation
• Organo-sulfur compounds from ocean phytoplankton