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Tracers with chemistry

The effects of chemistry are shown in Figure 5. In the following sections, the expression of effective mean age shall be used for age values derived when chemical loss is included. Scenario S8 has been left out in the figure, as the difference between S7 and S8 is typically smaller than 0.2 y up to 30 km. This value is only exceeded in the polar night where chemical tracers show much higher differences to the observations. The modelled profiles of the different chemistry scenarios are interpolated to the location of observation. Consequently, the information about the neighbourhood is not shown in this plot. Generally, the chemical loss is supposed to be most pronounced for polar winter profiles after the descent of air masses in the polar vortex region, which is clearly seen in Figure 5 for profiles taken in polar winter/spring. But even for tropical profiles, chemical loss is observed for scenario S1. For the comparison with the model tracers including chemistry, only some profiles are selected. The tropical profile P12 shows very good agreement with the observation up to 25 km. Above, the model shows an effective mean age up to one year higher than observed for all chemistry scenarios. For scenario S1, however, the effective mean age is 2.5 years too high. In this scenario a purely destructive attachment reaction is assumed. As no -stabilizing reaction is included, this chemistry scenario gives the maximum loss for a given electron profile. This large difference shows that the possibility of an attachment reaction without reactions reforming can be excluded. For the chemistry scenario S3, also a strong loss is expected, as only the destructive reaction with and the weak version of the charge exchange reaction with are included. This can be seen in the profiles P6 above 25 km and P15 at 27.5 km. Both observations are taken at midlatitudes and exhibit an undisturbed profile above 23 km. Here, S3 and S5 significantly deviate from the observations, but the inert profile and the more stable chemistry profiles are still compatible.