Microlightning: Avalanche-Driven Blue Emission and Reactive-Species Formation in Charged Microdroplets

Charged microdroplets have recently been observed in experiments performed without a strong externally imposed field to emit flashes of blue light and initiate chemical reactions, a new phenomenon referred to as “<i>microlightning</i>.” This observation adds to a growing body of evidence that charged microdroplets can host redox chemistry not accessible in bulk solution, yet the mechanistic origin and chemical consequences of this emission remain poorly understood.

A fundamental chemical question regarding spontaneous microdroplet reactivity thus naturally arises: can electrostatic energy stored on a microdroplet be converted into chemical activation, including molecular excitation, ionization, and reactive-species formation? Here, we establish a framework that links droplet charging, avalanche dynamics, and the resulting reactive-species and photon production. Under the local-field approximation, Townsend theory establishes analytical scaling for finite avalanches in isolated heavily charged droplets; particle-in-cell Monte Carlo simulations quantify multiplication up to ∼1000 and resolve electron fates via ionization, excitation, and attachment, generating reactive oxygen and hydrogen species (e.g., OH^•, O₂^•–, and H^•) or their precursors relevant to microdroplet-accelerated organic reactions and atmospheric chemistry.