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Accurate quasar classifications and redshift measurements are increasinglyimportant to precision cosmology experiments. Broad absorption line (BAL)features are present in 15-20\% of all quasars, and these features canintroduce systematic redshift errors, and in extreme cases producemisclassifications. We quantitatively investigate the impact of BAL features onquasar classifications and redshift measurements with synthetic spectra thatwere designed to match observations by the Dark Energy Spectroscopic Instrument(DESI) survey. Over the course of five years, DESI aims to measure spectra for40 million galaxies and quasars, including nearly three million quasars. Oursynthetic quasar spectra match the signal-to-noise ratio and redshiftdistributions of the first year of DESI observations, and include the samesynthetic quasar spectra both with and without BAL features. We demonstratethat masking the locations of the BAL features decreases the redshift errors byabout 1\% and reduces the number of catastrophic redshift errors by about 80\%.We conclude that identifying and masking BAL troughs should be a standard partof the redshift determination step for DESI and other large-scale spectroscopicsurveys of quasars.

Analysis of the impact of broad absorption lines on quasar redshift measurements with synthetic observations