This presentation consists of two parts. The first examines whether the meteoric metal layers are sensitive indicators of long-term changes in the upper mesosphere. Output from the Whole Atmosphere Community Climate Model (WACCM) is used to assess the response of the Na, K and Fe layers across a 50-year period (1955-2005), while both model and observational data is used to assess the response of the Na and K layers to the 11-year solar cycle. K displays a much more pronounced response to atmospheric changes on a 50-yr time scale than either Na or Fe, with a predicted increase in column density of 3.5±0.4% decade^-1, mostly arising from the modelled cooling trend of -0.2 to -0.5 K decade^-1 between 80 and 100 km.

The second part examines the removal of the potent greenhouse gases SF₆, NF₃ and CFC-115 in the middle atmosphere. The D region electron concentration is determined using a new version of WACCM with over 300 ion-molecule reactions from the Sodankylä Ion and Neutral Chemistry model. Electron attachment is the major route for SF₆ removal, while photolysis and reaction with O(¹D) largely remove NF₃ and CFC-115. The SF₆ lifetime is (1305 ± 143) years, much shorter than the currently recommended value of 3200 years. The lifetime of NF₃ is (616 ± 34) years, and that of CFC-115 is (492 ± 22) years. Their 100-year global warming potentials are then 22,800, 20,100 and 7630, respectively.