Measurements of mid-stratospheric formaldehyde from the Odin/SMR instrument

Measurements of mid-stratospheric formaldehyde (H₂CO) have been obtained from the limb-viewing sub-millimeter radiometer (SMR) instrument aboard the Odin satellite. The analysis is based upon the only weak (8₀₈→7₀₇) rotational transition line of H₂CO that can be measured by Odin/SMR at 576.7083150 GHz in the band dedicated to the measurement of carbon monoxide (CO). The signal-to-noise ratio is increased by averaging about 1000 spectra within 2-km width vertical layers in the stratosphere over periods from 1 to 7 days and within 3 latitude bands: Southern Hemisphere (90°S-45°S), tropics (30°S-30°N), and Northern Hemisphere (45°N-90°N). The faint H₂CO line can then be retrieved using the standard scientific ground-segment developed for the Odin/SMR measurements. The mid-stratospheric H₂CO shows maxima in the tropics for every period considered (January 2006, February 2005, March 2005, and September 2005). The spring-time extra-tropical mid-stratospheric H₂CO is more intense than the fall-time extra-tropical amounts. The simulations from the three-dimensional chemical-transport model Reprobus satisfactorily show these general features.