MOGUNTIA has a rather coarse resolution of 10-10 degrees and 10 vertical levels. The model uses pressure coordinates that range from 1000 hPa (roughly the earth surface) to 100 hPa (about 16 km). These pressure levels define the troposphere (and a part of the stratosphere). The mixing is much more efficient in the troposphere than in the overlying stratosphere. Chemically speaking, there are also big differences between the stratosphere and the troposphere. Due to the presence of the ozone layer in the stratosphere, much less radiation reaches the troposphere and the photochemistry is markedly different. Water vapor is also much more abundant in the troposphere.