Programme Topic 3: Trace gas and aerosol processes in the troposphere

It is generally accepted that the change in tropospheric air composition is connected with the increasing world population and its growing demand for energy, food and living space. These demands are associated with growing industrialization and urbanization, developing megacities, increasing traffic, and general land-use change. It has resulted in changing emissions of primary trace gases and aerosols into the troposphere, with direct impact on atmospheric chemical processes that control the removal of greenhouse gases and pollutants from the atmosphere (atmospheric self-cleaning), but also the chemical formation of new pollutants in the atmosphere like ozone or secondary organic aerosols (SOA).

The Institute of Meteorology and Climate Research contributes to Topic 3 with all its divisions IMK-AAF, IMK-TRO, IMK-ASF, and IMK-IFU.

The tropospheric chemistry and transport processes involved in atmospheric composition change occur on relatively short time scales (from minutes to years), thus resulting in a fast transformation and distribution of trace substances over regional and global scales. The influence of atmospheric chemistry on air quality and climate is further complicated by feed-back mechanisms on longer time scales.

Continuous and long-term monitoring is an important requirement to be able to inform policy makers about the state of the atmosphere and its changes over time and in response to policy measures. The need for sustainable operation of large research infrastructures and measurement facilities for Earth observations is therefore recognised world wide as an important challenge and is coordinated internationally.

Tropospheric aerosols are multi-phase, multi-component systems, either internally or externally mixed with natural and man-made contributions. This complexity is the reason for major gaps in our understanding of number, mass and composition of aerosols in the troposphere, especially of the organic aerosol components. In order to assess the impacts of aerosols on radiative transfer, cloud formation, and human health, it is necessary to understand the sources of primary aerosols, as well as the oxidative processes which generate new, secondary aerosols and transform the aerosols during their atmospheric lifetime.

Topic 3 investigates the chemical and microphysical processes of anthropogenic and biogenic trace substances and their effect on the self cleaning capability, the formation of aerosol, and the radiation balance in the troposphere. The overall goal is to improve the predictability of the atmospheric chemical state in a changing climate.

Scientific activity concentrates on the lower part of the troposphere, where most of the trace substances are reacting, secondary products are formed, and the physical and chemical properties of aerosol (cloud formation and radiation budget) are modified. In addition, long-term measurements of selected, chemically and climatically important trace substances in the free troposphere and lower stratosphere are performed using aircraft. Regional and global models will be tested and improved by experimental process studies and atmospheric observations. Specialised measurement systems for atmospheric trace substances will be developed and used on airborne platforms (e.g. research aircraft HALO) and in the aerosol simulation chamber AIDA.

Responsible and contact: Prof. Dr. Hans Peter Schmid (IMK-IFU), Prof. Dr. Thomas Leisner (IMK-AAF), Prof. Dr. Christoph Kottmeier (IMK-TRO)