Ground-based detection of stratospheric ClO and average column density measurement over 17 days of observation

A very sensitive mm-wave heterodyne receiver of a type originally developed for radio astronomy is used in combination with a broadband filter bank spectrometer to detect and measure the 204-GHz rotational transition of stratospheric ClO. Data is acquired in the form of a dimensionless ratio and is converted to units expressing signal intensity. Computed line shapes are matched against the data for a comparison with theoretical stratospheric models and previous measurements. The ClO distribution in the stratosphere measured at 42 deg N latitude in early spring is significantly different from that expected based on existing theoretical models. There is much less ClO at latitudes below about 36 km than predicted, and average ClO column density found for 42 deg N is 20-30% less than that from existing balloon flight measurements at 32 deg N.