Stratospheric calcite injection uses micro ground limestone and has similar reflectivity and longevity to sulfate aerosols, but does not deplete stratospheric ozone like sulfates. It actually helps to restore lost stratospheric ozone. from the abstract, ” Injecting sulfate aerosol into the stratosphere, the most frequently analyzed proposal for solar geoengineering, may reduce some climate risks, but it would also entail new risks, including ozone loss and heating of the lower tropical stratosphere, which, in turn, would increase water vapor concentration causing additional ozone loss and surface warming. We propose a method for stratospheric aerosol climate modification that uses a solid aerosol composed of alkaline metal salts that will convert hydrogen halides and nitric and sulfuric acids into stable salts to enable stratospheric geoengineering while reducing or reversing ozone depletion. Rather than minimizing reactive effects by reducing surface area using high refractive index materials, this method tailors the chemical reactivity. Specifically, we calculate that injection of calcite (CaCO3) aerosol particles might reduce net radiative forcing while simultaneously increasing column ozone toward its preanthropogenic baseline.”
Keith et al., Stratospheric solar geoengineering without ozone loss, PNAS, December 12, 2016.
https://www.pnas.org/content/pnas/113/52/14910.full.pdf
