First trace gas measurements using Fourier transform infrared solar absorption spectroscopy at the University of Toronto atmospheric observatory.

摘要

A new high-resolution (0.004 cm-1) research-grade Fourier transform spectrometer was installed at the University of Toronto Atmospheric Observatory (TAO), and commissioned in October 2001. TAO fills a coverage gap in North America in the Network for the Detection of Atmospheric Composition Change (NDACC), and was accepted as a Complementary Station in March 2004 as a direct result of work presented in this thesis.; Trace gas concentrations are derived using an existing Optimal Estimation Method (OEM) retrieval algorithm implemented at TAO as part of this work. A set of prior constraints necessary for retrievals of vertical profiles of trace gases using the OEM approach was optimized, and includes a priori volume mixing ratio profiles suited to TAO's location, and the prior and measurement noise covariances. A three-year time series of O3, NO. NO2, HCl, HF, N2O and CH4 (exhibiting the known seasonal cycles) was submitted to the NDACC database for long-terra monitoring, trend detection, and satellite validation purposes. A quantitative retrieval characterization was performed whereby the averaging kernels, weighting functions, measurement, smoothing and temperature error covariances of the retrievals of these seven gases were calculated. The degrees of freedom for signal ranged from 1.10 for NO2 to 4.12 for N2O.; A systematic study showed that the effect of several different layering schemes (implicit retrieval constraints) on the retrieved vertical profile is less than 5% for N2O and HF, and less than 2% for NO, NO 2, CH4 and HCl; however, retrieved profiles of H2O showed differences up to 13% when the layering scheme was varied. A maximum tropospheric layer thickness of 0.8 km is inferred for accurate H2O retrievals.; Finally, the usefulness of Fourier Transform InfraRed (FTIR) observations for studying different regions of the atmosphere was demonstrated by (1) documenting a limited sensitivity of ground-based measurements to mesospheric-lower thermospheric concentrations of NO, (2) correlating anomalously high stratospheric HCl, HF and O3 concentrations derived at TAO with the passage of a polar air filament above Toronto, and (3) showing very good agreement between monthly mean abundances of tropospheric CO between January 2002--September 2003 and spatially coincident MOPITT satellite measurements.