Proposed solar radiation modification (SRM) field experiments are receiving growing scientific and policy attention, with several localized experiments having occurred or under development. While they may be critical for improving technical understanding and reducing uncertainties, SRM field experiments remain controversial and inadequately captured under current legal, ethical, and political frameworks, which often rely on binary “small-scale” or “large-scale” distinctions. In practice, SRM field experiments may vary widely in scale, geography, materials, scientific purpose, and environmental impacts, making uniform governance approaches impractical. Here, we develop a typology of plausible, scientifically motivated SRM field experiments across three leading approaches: stratospheric aerosol injection (SAI), marine cloud brightening (MCB), and cirrus and mixed-phase cloud thinning (CCT/MCT). We identify six SAI, five MCB, and three CCT/MCT experiments across a range of scales, assessing their interaction with existing environmental and legal frameworks, particularly within the EU. The study also addresses governance challenges such as scale perception and stakeholder legitimacy, and highlights procedural tools, including exit ramps and transparency requirements. We introduce a phase-based typology of plausible SRM field experiments: near-phase (technically and regulatorily feasible), intermediate-phase (technically feasible but likely to cross regulatory thresholds), and distant-phase (plausible but requiring comprehensive review and new governance mechanisms). The intermediate-phase highlights that SRM research cannot be reduced to a small-/large-scale binary: many plausible experiments occupy a gray zone where scientific value is high, but governance remains underdeveloped. Recognizing this distinction may help prioritize governance, guide proportionate regulation, and ensure field experiments are evaluated by intent and their regulatory implications.

The open-source Video In Situ Snowfall Sensor (VISSS) is introduced as a novel instrument for the characterization of particle shape and size in snowfall. The VISSS consists of two cameras with LED backlights and telecentric lenses that allow accurate sizing and combine a large observation volume with relatively high pixel resolution and a design that limits wind disturbance. VISSS data products include various particle properties such as maximum extent, cross-sectional area, perimeter, complexity, and sedimentation velocity. Initial analysis shows that the VISSS provides robust statistics based on up to 10000 unique particle observations per minute. Comparison of the VISSS with the collocated PIP (Precipitation Imaging Package) and Parsivel instruments at Hyytiälä, Finland, shows excellent agreement with the Parsivel but reveals some differences for the PIP that are likely related to PIP data processing and limitations of the PIP with respect to observing smaller particles. The open-source nature of the VISSS hardware plans, data acquisition software, and data processing libraries invites the community to contribute to the development of the instrument, which has many potential applications in atmospheric science and beyond.

There are obstacles in better understanding the climate impacts associated with new materials that could be used for Stratospheric Aerosol Injections (SAI), like the lack of an integrated framework that combines climate modeling across scales, laboratory studies and small-scale field experiments. Vattioni et al. (2023, https://doi.org/10.1029/2023gl105889) explored one aspect of using alternative, non-sulfate materials for SAI. They investigated how uncertain the response of stratospheric ozone would be to alumina injections for SAI. In their study, they quantify chlorine activation rates in the presence of alumina, and then cascade these uncertainties into estimates of ozone depletion, concluding that alumina might have less detrimental impacts on stratospheric chemistry than sulfate, but with large uncertainties. Their results provide a useful basis upon which future research endeavors combining indoor and outdoor experiments and modeling may be structured to produce robust assessments of SAI impacts, benefits and uncertainties, together with clarifying what kind of research needs to be prioritized.