Size distribution curves
Figure 6 shows the size distribution curves, measured as
electrical mobility diameter and expressed as number of
particulate per cubic centimeter of air, for conditions 1 to 4.
In each condition, sampling was made before welding
operation (indicated in red) and also during welding
(indicated in blue). The existence of deposition/resuspension
phenomena can also be noticed in terms of fine particles size
distribution, as shown in Figure 4: for each condition, binodal
distributions can be observed, corresponding to two welldefined
size ranges: a set of fine particles, clearly within the
nanorange (in these cases, less than 40–50 nm) and another set
somewhat larger (around 180–200 nm). The large number of
particles in the nanorange occurs for condition 1, while the
number of smaller particles for conditions 2, 3 and 4 is
approximately the same. This type of distribution seems to
point out for the existence of other phenomena, apart from
deposition/re-suspension, which could be a consequence of
the aggregation of fine particles that was observed in TEM
images of collected particles.