  Bubbles are ubiquitous in many natural and engineering processes, and bubble
bursting aerosols are of particular interest because of their critical role in
mass and momentum transfer across interfaces. All prior studies claim that
bursting of a millimeter-sized bare bubble at an aqueous surface produces jet
drops with a typical size of $\boldsymbol{O}$(100 $\si{\micro\relax}$m), much
larger than film drops of $\boldsymbol{O}$(1 $\si{\micro\relax}$m) from the
disintegration of a bubble cap. Here, we document the hitherto unknown
phenomenon that jet drops can be as small as a few microns when the bursting
bubble is coated by a thin oil layer. We provide evidence that the faster and
smaller jet drops result from the singular dynamics of the oil-coated cavity
collapse. The unique air-oil-water compound interface offers a distinct damping
mechanism to smooth out the precursor capillary waves during cavity collapse,
leading to a more efficient focusing of the dominant wave and thus allowing
singular jets over a much wider parameter space beyond that of a bare bubble.
We develop a theoretical explanation for the parameter limits of the singular
jet regime by considering the interplay among inertia, surface tension, and
viscous effects. As such contaminated bubbles are widely observed, the
previously unrecognized fast and small contaminant-laden jet drops may enhance
bubble-driven flux across the interface, contributing to the aerosolization and
airborne transmission of bulk substances.
