Abstract
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 (PM2.5). 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 BetaPlus particulate monitor was used to collect PM2.5 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 PM10 (particles < 10 µm in aerodynamic diameter) pre-impactors and PM2.5 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.
Highlights
When primary particles collide and stick together, agglomerates or aggregates can form, creating complex structures (Kulkarni et al, 2011a)
The instrument used at PEAV was located at the lowerelevation site (UNRG) with another Teledyne Advanced Pollution Instrumentation (TAPI) instrument, before and after it was located at PEAV
Correlation between this instrument and the TAPI instrument located at UNRG was high before (r2 = 0.80, p < 0.05, n = 6) and after (r2 = 0.88, p < 0.05, n = 71) it was located at PEAV, indicating that the two instruments were operating (Pierce and Gustin, 2017)
Summary
When primary particles collide and stick together, agglomerates or aggregates can form, creating complex structures (Kulkarni et al, 2011a). Agglomerate particles can be categorized as branched-chain or compact aggregates (Kulkarni et al, 2011a). Large-scale, turbulent fires provide vortices where soot aggregates (∼ 100 s of monomers) can be trapped in a high particle to volume area, creating superaggregates consisting of thousands of monomers (Chakrabarty et al, 2014; Kearney and Pierce, 2012; Kulkarni et al, 2011a). One Teledyne Advanced Pollution Instrumentation (TAPI) 602 BetaPlus particulate monitor was located at a high-elevation site on Peavine Peak, NV, USA (PEAV) and another TAPI was located at a lower-elevation site ∼ 12 km southeast in Reno, NV, USA (UNRG), to collect particles < 2.5 μm in aerodynamic diameter (PM2.5).
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