Aggregated particles caused by instrument artifact
2018
Abstract. Previous studies have indicated that superaggregates, clusters of aggregates
of soot primary particles, can be formed in large-scale turbulent fires. Due
to lower effective densities, higher porosity, and lower aerodynamic
diameters, superaggregates may pass through inlets designed to remove
particles 2.5 µm in aerodynamic diameter ( PM 2.5 ).
Ambient particulate matter samples were collected at Peavine Peak, NV, USA
(2515 m ) northwest of Reno, NV, USA from June to November 2014. The
Teledyne Advanced Pollution Instrumentation (TAPI) 602 Beta Plus
particulate monitor was used to collect PM 2.5 on two filter types.
During this time, aggregated particles > 2.5 µm in aerodynamic
diameter were collected on 36 out of 158 sample days. On preliminary
analysis, it was thought that these aggregated particles were
superaggregates, depositing past PM 10 (particles
10 µm in aerodynamic diameter) pre-impactors and
PM 2.5 cyclones. However, further analysis revealed that these
aggregated particles were dissimilar to superaggregates observed in previous
studies, both in morphology and in elemental composition. To determine if the
aggregated particles were superaggregates or an instrument artifact, samples
were investigated for the presence of certain elements, the occurrence of
fires, high relative humidity and wind speeds, as well as the use of
generators on site. Samples with aggregated particles, referred to as
aggregates, were analyzed using a scanning electron microscope for size and
shape and energy dispersive X-ray spectroscopy was used for elemental
analysis. It was determined, based on the high amounts of aluminum present in the
aggregate samples, that a sampling artifact associated with the sample inlet
and prolonged, high wind events was the probable reason for the observed
aggregates.
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