Compared with background particle concentrations,
the GMAW process is able to generate high number,
surface area, and MCs of nanoparticles. The size
distribution, morphology, and chemical compositions
of welding particles are significantly different from
indoor and outdoor background particles. A bimodal
size distribution by mass and a unimodal size distribution
by number for welding nanoparticles were
observed. Welding particle’s morphology is dominated
by the cluster of nanoparticles, presented as
chain-like structure. Particle evolution involves three
modes of size distributions, i.e., primary nanoparticles,
agglomeration, and coarse particles. Working
activities, sampling distance from sources, air velocity,
background particles, and engineering control
measures have significant influence on nanoparticle
levels in workplace atmosphere. Number and SACs
are better exposure metrics for exposure assessment of
nanoparticles than MC. It is recommended that a
combination of multiple metrics is measured as part of
a well-designed sampling strategy for airborne nanoparticles.
Key exposure factors, such as particle
agglomeration/aggregation, background particles,
working activities, temporal and spatial distributions,
air velocity, and engineering control measures, should
be evaluated when measuring workplace exposure to
nanoparticles. This study also provides a set of
baseline exposure data for welding nanoparticles that
can be used for further epidemiological investigation
of welding-related diseases. However, a few limitations
should be pointed out: (1) the exposure data for
welding nanoparticles was obtained from static measurements,
and should be carefully interpreted as
estimates of personal exposure; (2) the sampling
design and evaluation of key exposure factors needs to
be further improved, such as paying more attention to
the influence of microclimatic conditions at working