This project proposes laboratory investigations of alternate materials with properties that may make them more suitable candidates for stratospheric SRM. Specifically, the project proposes studies that address direct physical risks associated with SRM, i.e., effects on stratospheric ozone and temperature, and consequences when particles settle through the lower stratosphere into the troposphere, i.e. impacts on tropospheric chemistry, composition and radiation. This only represents one vignette of the risks associated with stratospheric SRM, but it is critical to quantify these risks as soon as possible to help evaluate the efficacy and risks of different stratospheric SRM strategies. These studies can rule out materials found to have clearly unsuitable properties, but field tests are required for materials that “pass” the laboratory stage, to quantify the risks in the actual environment.