contact:Martin G. Schultz

Max Planck Inst. f. MeteorologyBundesstr. 55

D−20146 Hamburg, Germanymartin.schultz@dkrz.de

Atmospheric Chemistry and Global ChangeMartin G. Schultz, Guy P. Brasseur, Johann Feichter, Claire Granier,

Judith J. Hoelzemann, Ulrike Niemeier, and Philip Stier

Ein Institut der Max−Planck GesellschaftAn institute of the Max Planck Society

Max−Planck Institut für MeteorologieMax Planck Institute for Meteorology

Motivation for global atmospheric chemistry modeling

The world increase in population and energy use,especially since the 1950’s, has led to significantconcentration changes of atmospheric pollutantsand aerosols. Concentrations of near surface ozone,NOx, and volatile organic compounds (VOC) have reached levels that are adverse to human health andfood production in various regions around the globe.

The deposition rates of species that are chemicallyproduced in the atmosphere, such as HNO3, NH3,and aldehydes, have increased due to the rise in precursor concentrations with consequences forfood production, ecosystem health, and water quality.

Changes in near surface pollutant concentrations canaffect the growth rate and the speciation of terrestrialvegetation, possibly amplifying the effects of globalwarming. This might change VOC emissions from the biosphere, and it could lead to migration of animalsand humans as well as the increased spread of diseases.

Gas−phase and aerosol species can often be trans−ported over long distances, so that regional pollution becomes a problem on the continental or global scale.

Radiatively active gases (ozone, methane, CO2) reaching the upper troposphere or lower stratosphere contribute to global warming. Increased aerosol loadings effect the Earth’s radiative budget in several ways; the overall effect is still not known.

Stratospheric ozone has decreased over the last two decades with direct consequences for UV radiation at the Earth surface and implications for the frequency of skin cancer and crop damage. There are feedbacks between stratospheric ozone levels and stratospheric cooling which need to be quantified.

Because of the sparsity of observations and the need toobtain a coherent view of the atmospheric chemicalcomposition on the global scale, we need to build andrun numerical models simulating the emissions, transport, chemical transformations, and loss processes of several gas−phase and aerosol compounds. Due to the complexity of the underlying issues and the inhomo−geneity of sources and meteorological parameters, such models need to provide a sufficient level of detail and spatial resolution.

At the MPIfM, Hamburg, we employ two different global models with different degrees of complexity with respect to meteorology and chemistry:

MOZART2 is a chemistry−transport model originallydeveloped at the National Center of Atmospheric Research in Boulder, USA. The model is driven withmeteorological fields from ECMWF, NCEP, or fromclimate simulations and offers a flexible scheme fordescribing the emissions and chemical transformationsof trace species. In the standard version of MOZART,52 tracers are carried through the model and theyreact in over 100 reactions.

ECHAM5 is a general circulation model which was originally based on the forecast model of the ECMWF. Several modules for individual tracer studies have been developed for an older version of the ECHAM model and are currently implemented into the new version. Within the next year, we plan to integrate the chemistry from the MOZART model into the ECHAM model in order to study interactive feedbacks between climate and chemistry, and to provide a common framework for global atmospheric chemistry modeling at the MPIfM and in other German research institutions.

Recent and ongoing activities with these models include:

forecasting of carbon monoxide concentrations for the planning of airborne field experiments (BIBLE, TRACE−P, MINOS) and analysis of the observed concentration patterns and trace gas budgets

investigation of the sources of ozone over Europe and assessment of the model’s ability to simulate ozone at individual measurement stations in Europe

analysis of the variability of the tropospheric chemical composition due to ENSO weather patterns

investigation of the interannual variability of the emissions from vegetation fires and their effect on the tropospheric chemical composition

investigation of the direct and indirect aerosol effect with a size−resolved aerosol model

investigation of the budget of nitrogen oxides in the upper troposphere

development of suitable evaluation strategies for satellite observations of the tropospheric chemical composition

Models and ongoing modeling studies

Figure 1

Processes affecting the concentration of trace gases and aerosol in the atmosphere

Figure 2

Spatial and temporal scales of relevance for atmospheric chemistry

Figure 3

Simplified scheme of the tropospheric ozone chemistry in a polluted atmosphere with focus on the HOx cycle and its coupling to the NOx cycle