DOAS (Differential Optical Absorption Spectroscopy) Measurements during CONTRAST (CONvective Transport of Active Species in the Tropics)

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As part of the larger CONTRAST (Convective Transport of Active Species in the Tropics) measurement campaign, which has the main objective of measuring the transport of reactive chemical species into the topical Tropopause Transition Layer (TTL) over the western Pacific warm pool, University of Colorado-Boulder researchers seek to measure the column abundances of a number of trace halogen compounds e.g., bromine oxide (BrO), iodine oxide (IO), chlorine dioxide (OClO) along with other trace gas species.During northern winter, surface tropospheric air masses containing these reactive gases may be preferentially transported by intense tropical convection high into the TTL lower stratosphere over the region of the Pacific warm pool. Here they may impact the chemistry of the lower stratosphere, including its ozone chemistry. The unique low-ozone environments in the upper troposphere are expected to result in very small levels of OH radicals, which can be expected to increase the lifetime of reactive gases whose main loss is through hydroxyl (OH) radical oxidation. The simultaneous occurrence of deep convection and prolonged lifetime of organic compounds in the TTL can have significant impact on the stratospheric halogen budget.The timing of the CONTRAST experiment has been designed to take advantage of collaborations with two international airborne studies planned for the same time and geographic location. These are the NASA EV1 project ATTREX (Airborne Tropical Tropopause Experiment) and the European CAST (Coordinated Airborne Studies in the Tropics). With complementary instrument payloads, coordinated flights of the NSF GV, the NASA Global Hawk and the UK BAE146 will provide an unprecedented examination of the full atmospheric column, from surface to 19 km, in the Tropical Western Pacific.