GBS (Ground-Based Spectrometer)

Eureka Station and Eureka GBS UV-VIS NDACC Metadata
Eureka GBS UV-VIS NDACC Rapid Delivery Data 

For more information about the PEARL FTS please contact Dr. Kimberly Strong

The PEARL Ridge Lab is home to two UV-visible ground-based spectrometer (GBS) instruments that measure scattered sunlight: the University of Toronto GBS (UT-GBS, installed in 1999) and the PEARL-GBS (installed in 2006; Fraser et al., 2009). Both instruments are grating spectrometers that disperse scattered light (much as a prism divides white light into a ‘rainbow’) based on the diffraction grating setting, followed by light detection to produce a spectrum that contains absorption features pertaining to trace gases in the atmosphere. Currently, the UT-GBS and PEARL-GBS gratings are set to measure scattered visible (approx. 1 nm resolution) and scattered UV light (approx. 0.5 nm resolution), respectively. The GBS instruments utilize suntrackers mounted within UV-transparent domes on the roof of the lab to operate in zenith-sky or off-axis viewing geometries. While zenith-sky (i.e., pointing directly upwards) measurements provide good sensitivity to stratospheric absorbers, off-axis (i.e., pointing at various elevation angles) measurements provide good sensitivity to the troposphere.

The UV-transparent dome, housing some of the input optics and suntracker, of the PEARL-GBS is mounted on the roof of the PEARL Ridge Lab. The UT-GBS rooftop configuration is identical.

The differential optical absorption spectroscopy (DOAS) method is used to convert raw spectra to differential slant column densities (dSCDs) of various trace gases. The UT-GBS provides dSCDs of ozone and NO2 with sensitivity to the stratosphere while the PEARL-GBS provides stratospheric NO2, OClO and BrO dSCDs as well as tropospheric BrO dSCDs. Using additional retrieval software and radiative transfer models, dSCDs can be converted to vertical column densities (VCDs) of ozone and NO2 as well as to vertical profiles of tropospheric BrO. Such long-term measurements have been used to investigate Arctic stratospheric ozone depletion during the spring as well as bromine explosion events which have been linked to severe surface ozone depletion events. Additionally, the measurements contribute to validation studies of satellite measurements from the Atmospheric Chemistry Experiment (ACE), Optical Spectrograph and Infra-Red Imager System (OSIRIS), and more recently, the Tropospheric Monitoring Instrument (TROPOMI). The instruments both measure during the sunlit portion of the year (late February to late March) and are certified instruments within the Network for the Detection of Atmospheric Composition Change (NDACC).

Both GBS instruments operate in zenith-sky (top) and multi- or off-axis (bottom) viewing geometries. Zenith-sky measurements collect scattered sunlight with the instrument input optics pointing in the zenith direction and provide stratospheric sensitivity due to longer optical paths in the stratosphere. Off-axis measurements collect scattered sunlight at various elevation angles and provide tropospheric sensitivity due to enhanced optical paths in the troposphere.