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Aircraft-borne DOAS limb observations of UV/visible absorbing trace gas species over Borneo: Implications for the photochemistry of iodine, volatile organic oxide degradation, and lightning-produced radicals

Großmann, Katja

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Abstract

Tropical deep convection is one of the major mechanisms for transporting trace gases from the lower to the upper troposphere and tropical tropopause layer (TTL). From there, they further ascend to the lowermost stratosphere by diabatic heating. Within this thesis, airborne spectroscopic measurements were carried out during the SHIVA (Stratospheric ozone: Halogen Impacts in a Varying Atmosphere) campaign at Malaysian Borneo in November and December 2011 in order to study the abundance and transport of trace gases in the lower atmosphere. Sixteen flights were performed with the research aircraft DLR-Falcon covering legs near the surface as well as in the free troposphere up to an altitude of 13 km. The measurements were evaluated using the Differential Optical Absorption Spectroscopy (DOAS) technique in limb geometry, which supports observations of UV/visible absorbing trace gases, such as O4, BrO, IO, NO2, HCHO, CHOCHO, HONO and H2O. Inferred vertical profiles of IO show mixing ratios of 0.5-1.5 ppt in the marine boundary layer decreasing to 0.1-0.3 ppt in the free troposphere. Thus, the main IO sources originate from near or at the surface. Enhanced IO concentrations occasionally occurred in the mid-troposphere, sometimes in coincidence with elevated concentrations of CO, suggesting rapid vertical transport by shallow to medium strong convection. Due to low concentrations of IO in the mid-troposphere over land together with short time scales for vertical and horizontal transport, it is concluded that efficient IO loss processes exist, preventing IO from reaching the TTL and stratosphere. BrO did not exceed the detection limit of approximately 2 ppt since in the terrestrial tropical atmosphere around Borneo the chemistry of volatile organic compounds (VOCs) acts as a large sink for reactive bromine species. CHOCHO and HCHO frequently exceeded Background concentrations. These observations indicate efficient VOC photochemistry, since CHOCHO and HCHO are mainly produced through the oxidation of VOCs emitted from the tropical rain forest of Borneo and from distinct anthropogenic sources. Signatures of HONO, HCHO, and NO2 in the outflow of convective clouds indicate a rapid transport of HCHO and NO2 from polluted near surface air into the upper troposphere as well as lightning-induced production of HONO and NOx.

Item Type: Dissertation
Supervisor: Pfeilsticker, Prof. Dr. Klaus
Date of thesis defense: 10 December 2014
Date Deposited: 18 Dec 2014 07:39
Date: 2014
Faculties / Institutes: The Faculty of Physics and Astronomy > Institute of Environmental Physics
Subjects: 530 Physics
Controlled Keywords: Physics
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