Bromine Chemistry in the Tropical UTLS during the 2011, 2013 and 2014 ATTREX Experiments

Abstract:

Bromine chemistry impacts the levels of ozone in the upper troposphere and the stratosphere. An accurate quantitative understanding of the sources, sinks, and chemical transformation of bromine species is thus important to understand the bromine budget in the upper troposphere and lower stratosphere (UTLS), which also serves as a gate to the stratosphere. Vertical transport of very short-lived organic bromine precursors, such as CHBr₃, CH₂Br₂ and inorganic product gases has been identified as the main source of bromine in the UTLS. However, the contribution of inorganic vs. organic compounds is not well quantified, particularly in the tropical UTLS. A number of chemical processes, including the role of ice particles for the transformation and cycling of inorganic bromine species are also poorly understood.

A limb scanning Differential Optical Absorption Spectroscopy Instrument was deployed on-board NASA’s unmanned high-altitude Global Hawk aircraft during the 2011, 2013, and 2014 NASA Airborne Tropical TRopopause EXperiment (ATTREX). Flights in the eastern and western Pacific were performed to study, among other topics, the chemistry of bromine and ozone in the subtropical and tropical UTLS. Here we will present observations of BrO, NO₂ and other trace species made by this instrument at altitudes between 15 – 20 km. The measurement methodology as well as the procedure to retrieve vertical trace gas concentration profiles will be briefly presented. The combination of those observations with the measurements of organic bromine species from the University of Miami’s Whole Air Sampler (GWAS) will be used to determine and interpret the bromine budget in the UTLS.