OH column abundance over Table Mountain Facility, California: Annual average 1997-2000

The column abundance of OH over Table Mountain Facility, California, (TMF) has been measured regularly since July 1997 using the Fourier‐transform Ultraviolet Spectrometer. The annual average OH column observed for 1998–2000 is 10–20% larger than that observed by another group over Tokyo for 1992–1995; 30–65% smaller than that observed by other groups over Colorado and New Mexico for 1980–1996; and 15–30% smaller than calculated by photochemical models. The Tokyo annual average and model estimates are within the range of geophysical variability for the OH column observed over TMF but the Colorado and New Mexico annual averages are not. This suggests the possibility of systematic errors in one or more of the data sets.