  We present a model for spectrophotometric calibration errors in observations
of quasars from the third generation of the Sloan Digital Sky Survey (SDSS-III)
Baryon Oscillation Spectroscopic Survey (BOSS) and describe the correction
procedure we have developed and applied to this sample. Calibration errors are
primarily due to atmospheric differential refraction and guiding offsets during
each exposure. The corrections potentially reduce the systematics for any
studies of BOSS quasars, including the measurement of baryon acoustic
oscillations using the Lyman-$\alpha$ forest. Our model suggests that, on
average, the observed quasar flux in BOSS is overestimated by $\sim 19\%$ at
3600 \AA\ and underestimated by $\sim 24\%$ at 10,000 \AA. Our corrections for
the entire BOSS quasar sample are publicly available.
