The variables at play are (1) the mass of material added, (2) the level of the atmosphere to which the material is added, (3) the specific chemistry of the material added, and (4) the potential effects (e.g., change in albedo, etc) of those materials as a function of time and concentration. The type and magnitude of effect will scale with the mass and whatever the particular material does, but points 2 and 3 are also important as they control the residence time (i.e., the duration). We could consider something like sulfate aerosols that are injected into the atmosphere during things like large impacts or large volcanic eruptions. Residence time for these depend a lot on the level of the atmosphere the particles are in, e.g., Junium et al., 2022 consider residence times for sulfate related to the Chicxulub impact and highlight that particles injected into the troposphere might last a few days to weeks, whereas those in the stratosphere would linger for months to years. The specific chemistry also matters though, so behavior of one type of particle is not representative for all, i.e., if the particle in question readily reacts with something, the residence time might change. All of this is to highlight the uncertainty, i.e., without dedicated experiments we don't know exactly what the effect will be and it's not necessarily safe to just assume that it will be negligible.