  We investigate mucosalivary dispersal and deposition on horizontal surfaces
corresponding to human exhalations with physical experiments under still-air
conditions. Synthetic fluorescence tagged sprays with size and speed
distributions comparable to human sneezes are observed with high-speed imaging.
We show that while some larger droplets follow parabolic trajectories, smaller
droplets stay aloft for several seconds and settle slowly with speeds
consistent with a buoyant cloud dynamics model. The net deposition distribution
is observed to become correspondingly broader as the source height $H$ is
increased, ranging from sitting at a table to standing upright. We find that
the deposited mucosaliva decays exponentially in front of the source, after
peaking at distance $x = 0.71$\,m when $H = 0.5$\,m, and $x = 0.56$\,m when
$H=1.5$\,m, with standard deviations $\approx 0.5$\,m. Greater than 99\% of the
mucosaliva is deposited within $x = 2$\,m, with faster landing times {\em
further} from the source. We then demonstrate that a standard nose and mouth
mask reduces the mucosaliva dispersed by a factor of at least a hundred
compared to the peaks recorded when unmasked.
