Halogen Oxide Measurements by Differential Optical Absorption Spectroscopy
PI: Udo Frieß
Participating Scientists: Udo Frieß, Holger Sihler
Research Website:
http://www.iup.uni-heidelberg.de
Contact:
Dr. Udo Frieß
Institute of Environmental Physics
University of Heidelberg
Im Neuenheimer Feld 229
69120 Heidelberg
Germany
Tel. 0049 - 6221 - 545478
Fax 0049 - 6221 - 546405
Email: udo.friess@iup.uni-heidelberg.de
Objectives:
The objective of our research activities is the experimental investigation of the role of reactive halogen compounds in the chemistry of the polar boundary layer and the free troposphere based on measurements of halogen radicals by Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). Growing evidence has emerged in recent years that the photochemistry of halogens might play an important role in the troposphere on a global scale. The consequences of the presence of re-active halogens in the troposphere are ranging from the destruction of ozone over changes in the bal-ance of important chemical families and the increased deposition of toxic compounds to a potential impact on global climate. However, measurements of halogens in the troposphere are still very sparse. It is therefore of vital importance for a better understanding of tropospheric photochemistry to obtain further insight into the processes reactive halogens are involved in. These processes will be studied during the OASIS 2009 campaign by performing both passive (MAX-DOAS) and active (Long-Path DOAS) measurements of tropospheric halogen compounds
Meaurement Technique:
Differential Optical Absorptions Spectroscopy (DOAS) is a remote sensing technique which allows to detect numerous atmospheric trace gases, such as BrO, IO, NO2, by their individual absorption features, either from spectrally resolved measurements of scattered sunlight (MAX-DOAS) or using artificial light sources (Long-Path DOAS).
Our Long-path DOAS instrument consists of a Newton- telescope, from which light from an arc lamp is sent to a retro reflector array located in a distance of several kilometres. From the spectral analysis of the reflected light, average concentrations of trace gases can be directly inferred.
The Multi-Axis DOAS instruments observe scattered sunlight from several directions between zenith and horizon using a moveable telescope. MAX-DOAS measurements have a very high sensitivity to absorbers located near the ground when observing light from close to the horizon (low elevation angle). By performing measurements at several elevation angles – from the horizon to the zenith – information on the vertical profile of the observed trace gases can be inferred using the variation of the length of the light path through the trace gas layer as a function of elevation angle.
The long-path DOAS telescope onboard the Amundsen ice breaker during the Circumpolar Flaw Lead Study (CFL) campaign in spring 2008.