AEROSOL EFFECTS AND CORRECTIONS IN THE HALOGEN OCCULTATION EXPERIMENT

The eruptions of Mt. Pinatubo in June 1991 increased stratospheric aer osol loading by a factor of 30, affecting chemistry, radiative transfe r, and remote measurements of the stratosphere. The Halogen Occultatio n Experiment instrument on board UARS makes measurements globally for inferring profiles of NO2, H2O, O-3, HF, HC1, CH4, NO, and temperature in addition to aerosol extinction at five wavelengths. Understanding and removing the aerosol extinction is essential for obtaining accurat e retrievals from the radiometer channels of NO2, H2O and O-3 in the l ower stratosphere since these measurements are severely affected by co ntaminant aerosol absorption. If ignored, aerosol absorption in the ra diometer measurements is interpreted as additional absorption by the t arget gas, resulting in anomalously large mixing ratios. To correct th e radiometer measurements for aerosol effects, a retrieved aerosol ext inction profile is extrapolated to the radiometer wavelengths and then included as continuum attenuation. The sensitivity of the extrapolati ons to size distribution and composition is small for certain waveleng th combinations, reducing the correction uncertainty. The aerosol corr ections extend the usable range of profiles retrieved from the radiome ter channels to the tropopause with results that agree well with corre lative measurements. In situations of heavy aerosol loading, errors du e to aerosol in the retrieved mixing ratios are reduced to values of a bout 15, 25, and 60% in H2O, O-3, and NO2, respectively, levels that a re much less than the correction magnitude.