Ground-based measurements of tropospheric CO, C2H6, and HCN from Australia at 34 S latitude during 1997-1998

High spectral resolution (0.004 cm−1) infrared solar absorption measurements of CO, C2H6, and HCN have been recorded with the Fourier transform spectrometer located at the Network for the Detection of Stratospheric Change complementary station at the University of Wollongong, Australia (34.45°S, 150.88°E, 30 m above sea level). The time series covers March 1997 to February 1998. Profile retrievals with maximum sensitivity in the upper troposphere show distinct seasonal cycles for all three molecules with maxima during October-December 1997. Best fits to the time series of daily averages yield peak 0.03–14 km columns (molecules cm−2) of 1.54×1018 for CO, 8.56×1015 for C2H6, and 6.56×1015 for HCN during austral spring. Mixing ratio profiles of all three molecules during this time show maxima in the upper troposphere. Isentropic back trajectories suggest the elevated CO, C2H6, and HCN columns above Wollongong originated from southern Africa or South America with no significant contribution from the intense tropical Asian emissions during the strong El Niño event of 1997–1998.