Stratospheric profiles

The Earth's atmosphere can be divided in several layers. The lowest layer is the troposphere. The Earth's surface forms the lower boundary of this layer and thus life is within this layer, but also all weather phenomena occur in here. The troposphere is characterized by decreasing temperature with increasing altitude. The altitude where this temperature decrease by altitude changes in an increase, is the upper boundary of the troposphere. This boundary is called the tropopause and is typically 8 km above sea level in polar regions and slowly increasing to 17 km towards tropical regions.

The next layer is the stratosphere and runs up to 50 km. In this layer the temperature increases with altitude and subsequently the atmospheric dynamics are compeletely different from the troposphere. For instance, vertical mixing of air occurs at a much lower rate than in the troposphere and the air is more or less layered or stratified, hence its
name.

Despite its altitude, and henceforward its low pressure, the stratosphere is of importance for us surface dwellers as it contains the ozone layer, which protects us against aggressive solar UV radiation. By complex chemical cycles stratospheric ozone can be destroyed by certain species that contain chlorine. Chlorine enters the stratosphere in the form of chlorofluorocarbons (CFCs) amongst others. Due to recent regularizations the emitted amount of CFCs has been decreased and it is therefore expected that the concentrations in the stratosphere will also drop. To monitor this decline, measurements of these trace gases in the stratosphere are necessary. As ozone is not equally distributed over altitudes it is not only of importance how much chlorine is in the stratosphere, but also at which altitudes. Such an altitude distribution is called a (stratospheric) profile.

The TErahertz and submillimeter LImb Sounder (TELIS) is a balloon-borne intsrument that measures profiles of several trace gases in the stratosphere. The instrument consists of three channels of which one is developed here at SRON. With respect to chlorine chemistry, TELIS is capable of measuring HCl, ClO, and HOCl.

But TELIS can measure a whole suit of trace gases: OH, H₂O (+ isotopomers), HO₂, H₂O₂, O₂, O₃ (+ isotopomers), HNO₃, NO, NO₂, N₂O, HNO₃, CO, and BrO. These gases can be used to address several science cases. E.g. water isotopomers can be used to investigate the entrance of tropospheric air into the stratosphere; a process that still is not fully understood. OH and HO₂ are involved in an other catalytic ozone destruction cycle. BrO can destroy ozone in a similar way to ClO, but the exact concentrations are not fully understood and might imply hidden processes. All in all, TELIS can contribute to a wide variety of science questions.