My talk summarizes recent work on interstellar gas-to-dust ratios at high Galactic latitude (Shull & Panopoulou 2024 ApJ, in press available on [ Ссылка ]). Interstellar dust at high Galactic latitudes can influence astronomical foreground subtraction, produce diffuse scattered light, and soften the ultraviolet spectra of quasars. In 94 sight lines toward quasars at high latitude and low extinction, the “gas-to-dust ratio” N_H / E(B-V) is 50% higher than its mean value 6.0x10^21 cm^-2 mag^-1 in the Galactic plane. Gas-to-dust ratios are especially elevated in sight lines with high-velocity clouds, which contribute N_H but little reddening. Decreases in dust content are expected in low-metallicity gas above the Galactic plane, resulting from grain destruction in shocks, settling to the disk, and thermal sputtering in hot halo gas.
