Atmospheric Physics and Chemistry Group

RESEARCH

The APCG uses innovative measurement techniques and comprehensive computer programs to investigate on global trace gas budgets, emissions from the biosphere and aerosol-cloud interaction. Individual projects target a wide range of research questions, as shown in the list below. An important tool of our group is the measurement of the isotopic composition of trace constituents, which we use to identify and quantify fluxes from individual sources and sinks. Although in the following the experimental and modeling themes are separated, in many subprojects we use an integral approach by combining measurements and modeling activities. This will become clear in the descriptions of several individual projects.

Experimental research:
Progress in atmospheric research is dependent on reliable, precise and innovative measurements. We have two experimental focus areas where we are among the world leaders in the development and application of new instrumentation:
1) The investigation of atmospheric trace gas cycles with isotope techniques
2) Organic trace gases in the atmosphere - their emissions from the biosphere and their role for aerosol formation
A large part of this work is fieldwork, where measurements are made, or samples are collected, at different parts of the globe, often in the framework of large international projects.

Laboratory:
Our group operates a large atmospheric chemistry laboratory with five isotope ratio mass spectrometers, one proton transfer reaction mass spectrometer and numerous sampling, extraction and preparation devices for isotope studies. We are a very innovative laboratory in the development of new techniques for atmospheric research and constantly work on new measurement methods. We integrate students into the research program at an early stage via experimental thesis projects and student assistantships.

Atmospheric modeling:
Computer models integrate the wealth of information that becomes available from measurements, and use this information to reproduce the atmospheric observations and help understand the underlying processes. Models exist at various stages of complexity, from simple box models to interactive global earth system models. The modeling activities in the APCG are centered on the following two themes:
3) Aerosol-cloud interaction: microphysics and global effects
4) Global greenhouse gas cycling and atmospheric chemistry

Projects under research

The investigation of atmospheric trace gas cycles with isotope techniques
Trace gases that are emitted from different sources usually have a slightly different isotopic composition. Therefore, isotope measurements can be used to quantify the emissions from the different sources. Also, when a trace gas is removed, the responsible removal reaction usually leaves a small fingerprint in the isotopic composition. Therefore, isotope measurements can provide information on individual source and sink processes, which are often not achievable by measurement of the concentration alone. Since this is a general property of isotope research, the isotope approach has a very wide range of applications, also outside of scientific research. In our group we use this technique to investigate the atmospheric cycles of many trace species. The following list contains the presently active research projects together with the name of the responsible researcher. Click the links to find specific information on those projects:

-    emissions of CH₄ from organic matter and plants
     Ivan Vigano

-    the budgets of methane and nitrous oxide in the pre-industrial period using air trapped in polar ice cores
     Celia Sapart

-    emissions of organic gases from organic matter upon irradiation with UV light
     Leonie Derendorp

-    Isotope measurements on volatile organic compounds in the atmosphere
     Adriaan Zuiderweg

-    The isotopic composition of the various sources and sinks of H₂
     Sylvia Walter

-    Investigation of the global hydrogen cycle with isotope measurements
     Anneke Batenburg

-    the transport of water vapour from the troposphere to the stratosphere

     Jörg Steinwagner

-    The oxygen isotope anomaly in atmospheric nitrate and N₂O
     Motoki Sasakawa

-    Sources and processing of carbonaceous aerosols studies with isotope measurements
     Ulrike Dusek

-    The fraction of fossil fuel emissions to the carbon aerosol in the Netherlands determined by ¹⁴C measurements
     Ulrike Dusek, Leonie Derendorp

Organic trace gases in the atmosphere - their emissions from the biosphere and their role for aerosol formation
(information available soon, for questions please contact Rupert Holzinger)

Aerosol-cloud interaction: microphysics and global effects
Clouds are an important factor in the Earth's radiation budget. Clouds reflect solar radiation and thus have a cooling effect. On the other hand, high cirrus clouds trap infrared radiation in the atmosphere which leads to warming, in a similar way as greenhouse gases. The first effect exceeds the second, so that the net effect of clouds is a cooling of the planet.

Clouds are a component of the Earth's hydrological cycle, acting as a sort of safety valve to keep the atmospheric burden of water vapor (an important natural greenhouse gas) within limits. Clouds are also directly linked to the biosphere and to surface characteristics. This is because cloud drops grow on aerosol, i.e., tiny particles that originate from natural processes (wind-blown desert dust and sea salt, volcanic eruptions, emssions from vegetation and plankton) and from human activities (fossil fuel burning, agriculture, traffic). The amount of aerosol influences the reflectivity and the potential for rain formation of a cloud.

Changes of the atmospheric composition and/or of the Earth's climate will result in a different occurrance and distribution of clouds and precipitation. In turn, this will directly affect the solar radiation available at the surface, the temperature and the biological activity, thus creating many possibilities for feedback loops within and inbetween different components of the climate system.

In view of the varying time and spatial scales involved in cloud formation, from tenths of micrometers to hundreds of kilometers and from seconds to days, and the multidisciplinarity involving physics, chemistry and biology, the study of clouds and their climate aspects is a very challenging one. Cloud research at IMAU focuses on aerosol-cloud interactions. We employ computer simulation models of varying complexity.

-    the IMAU cloud parcel model; this represents in large detail the cloud microphysical processes, i.e., activation of aerosol to cloud drops, condensational growth, precipitation formation in aqueous phase chemistry. This model is applied in ongoing research and is also highly suitable for student projects.

-    a 1D cloud column model with explicit microphysics, applied in a Ph.D. project.

-    a global climate model with explicit representation of aerosol formation, transformation and removal (ECHAM5-HAM) with a cloud processing parameterization that is developed and implemented by IMAU.



Global greenhouse gas cycling and atmospheric chemistry

-   Carbon Monoxide from Biomass Burning: Estimating the source and variability using SCIAMACHY and MOPITT measurements
    Pim Hooghiemstra