Preview

PDF, English Download (18MB) | Terms of use

Abstract

The present thesis reports on the world's first measurements of the second most important ozone-depleting halogen bromine at the entrance to the stratosphere (14 - 18.5 km, theta = 330 - 400 K) over the East and Central Pacific in late winter 2013. The measurements were performed within the NASA-ATTREX project from aboard the unmanned aerial vehicle Global Hawk. For the interpretation of the remote-sensing DOAS measurements of O3, NO2 and BrO, use of complementary measurements of brominated source gases (SGs) and dynamical tracers (e.g. CH3Br, halons, very short-lived species (VSLS), CH4) and model simulations of the chemical transport model (CTM) SLIMCAT/TOMCAT, is made. The agreement of measured and modelled CH4, O3, and NO2 shows that the major dynamicaland photochemical processes are represented well in the CTM. Considering surface concentrations of the brominated organic SGs of in total 20.5 ppt, the measured BrO mixing ratios (0.5 - 9.0 ppt) are well explained. An exception are regions where the contribution of the short-lived CH2Br2 or the partitioning of BrONO2 plays an important role. The present observations confirm previous findings on the formation of BrONO2 of our workgroup. Depending on the flight, a total bromine budget (Bry) in the tropical tropopause layer (TTL) of 20.3 ppt to 22.3 ppt is inferred. For each fligh the contribution to total bromine of the long-lived brominated SGs stays constant (CH3Br + halons = 14.6 ppt), while the amount of VSLS and inorganic bromine varies between 5.7 ppt and 7.7 ppt. Thus, the present observations set a tighter constraint on the role of bromine for ozone depletion in the TTL than previous studies.