Distribution and budget of O 3 in the troposphere calculated with a chemistry general circulation model (original) (raw)

1995, Journal of Geophysical Research

We present results of global tropospheric chemistry simulations with the coupled chemistry/atmospheric general circulation model ECHAM. Ultimately, the model will be used to study climate changes induced by anthropogenic influences on the chemistry of the atmosphere; meteorological parameters that are important for the chemistry, such as temperature, humidity, air motions, cloud and rain characteristics, and mixing processes are calculated on-line. The chemical part of the model describes background tropospheric CH4-CO-NOx-HOx photochemistry. Emissions of NO and CO, surface concentrations of CH4, and stratospheric concentrations of 03 and NOy are prescribed as boundary conditions. Calculations of the tropospheric 03 budget indicate that seasonal variabilities of the photochemical production and of injection from the stratosphere are represented realistically, although some aspects of the model still need improvement. Comparisons of calculated 03 surface concentrations and 03 profiles with available measurements show that the model reproduces 03 distributions in remote tropical and midlatitudinal sites. Also, the model matches typical profiles connected with deep convection in the Intertropical Convergence Zone (ITCZ). However, the model tends to underestimate 0 3 concentrations at the poles and in relatively polluted regions. These underestimates are caused by the poor representation of tropopause foldings in midlatitudes, which form a significant source of tropospheric 03 from the stratosphere, too weak transport to the poles, and the neglect of higher hydrocarbon chemistry. Also, mixing of polluted continental boundary layer air into the free troposphere may be underestimated. We discuss how these model deficiencies will be improved in the future. 20,983 20,984 ROELOFS AND LELIEVELD: TROPOSPHERIC O3 IN A CHEMISTRY GCM Institute for Meteorology in Hamburg, Germany [Roeckner et al. , 1992]. All meteorological data needed to evaluate chemical tracer concentrations in the atmosphere are calculated on-line by ECHAM with a time resolution of 40 min. As a result of the meteorology calculations, more CPU time is required than with an off-line model with the same spatial resolution and chemistry. In our model the calculations associated with chemical species (i.e., the processes described in section 2 and transport in the atmosphere) need approximately the same amount of CPU time as the meteorology calculations. However, the use of an off-line model requires substantial CPU time and memory to read and store data for the calculation of transport and the complex interactions between meteorological and chemical processes, whereas a large amount of data may be needed to cover different model resolutions. Further, a chemistry GCM interactively calculates concentrations of radiatively active species such as 03 that directly drive the radiation scheme and the GCM meteorology. When fully developed and tested, a coupled chemistry GCM is a powerful tool in the study of the intricate interactions between atmospheric chemistry and global climate.