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We present 1-mm observations constructed from ALMA [Atacama Large(sub)Millimeter Array] data of SO$_2$, SO and KCl when Io went from sunlightinto eclipse (20 March 2018), and vice versa (2 and 11 September 2018). Thereis clear evidence of volcanic plumes on 20 March and 2 September. The plumesdistort the line profiles, causing high-velocity ($\gtrsim$500 m/s) wings, andred/blue-shifted shoulders in the line profiles. During eclipse ingress, theSO$_2$ flux density dropped exponentially, and the atmosphere reformed in alinear fashion when re-emerging in sunlight, with a "post-eclipse brightening"after $\sim$10 minutes. While both the in-eclipse decrease and in-sunlightincrease in SO was more gradual than for SO$_2$, the fact that SO decreased atall is evidence that self-reactions at the surface are important and fast, andthat in-sunlight photolysis of SO$_2$ is the dominant source of SO.Disk-integrated SO$_2$ in-sunlight flux densities are $\sim$2--3 times higherthan in-eclipse, indicative of a roughly 30--50\% contribution from volcanicsources to the atmosphere. Typical column densities and temperatures are $N\approx (1.5 \pm 0.3) \times 10^{16}$ cm$^{-2}$ and $T \approx 220-320$ K bothin-sunlight and in-eclipse, while the fractional coverage of the gas is 2--3times lower in-eclipse than in-sunlight. The low level SO$_2$ emissions presentduring eclipse may be sourced by stealth volcanism or be evidence of a layer ofnon-condensible gases preventing complete collapse of the SO$_2$ atmosphere.The melt in magma chambers at different volcanoes must differ in composition toexplain the absence of SO and SO$_2$, but simultaneous presence of KCl overUlgen Patera.

ALMA Observations of Io Going into and Coming out of Eclipse