The complexity of aerosol production from bubble bursting

For La < 10⁴, Jiang et al. (1) correctly state that their 73-, 137-, and 199-micron bubbles would produce daughter bubbles whose jet droplets would yield particles of 24, 52, and 83 nm, respectively. However, in contrast with the general inconsistency claimed by Jiang et al. for jet droplets, these values agree with their experimental peaks at about 35, 50, and 80 nm (ref. 1, figure 2).

Fig. 1 shows additional published data for bubble jetting. Since Jiang et al. (1) cannot experimentally discriminate the mechanism producing their aerosols, their measurements should reproduce the number of jet droplets that others report for La < 10⁴ (4–6). However, Jiang et al.’s values for La < 10⁴ are at least 30 times smaller. This major experimental inconsistency suggests a possible underperformance of their scanning mobility particle sizer and aerodynamic particle sizer equipment or the inadequate measurement of bubble sizes actually bursting at the water surface. In effect, complex mechanisms involving water supersaturation with air, bubble coalescence, and daughter formation at the water surface (6–8) cannot be ruled out. Hence, the bubble size distribution actually bursting at the surface (7, 8) for their La > 10⁴ range may contain an indeterminate but significant fraction of bubbles in the actual range La < 10⁴.