Simultaneous Measurement of the Effective Density and Chemical Composition of Ambient Aerosol Particles

Abstract

Simultaneous measurements of the effective density and chemical composition of individual ambient particles were made in Riverside, California by coupling a differential mobility analyzer (DMA) with an ultrafine aerosol time-of-flight mass spectrometer (UF-ATOFMS). In the summer, chemically diverse particle types (i.e., aged-OC, vanadium-OC-sulfate-nitrate, biomass) all had similar effective densities when measured during the same time period. This result suggests that during the summer study the majority of particle mass for the different particle types was dominated by secondary species (OC, sulfates, nitrates) of the same density, while only a small fraction of the total particle mass is accounted for by the primary particle cores. Also shown herein, the effective density is a dynamic characteristic of the Riverside, CA ambient aerosol, changing by as much as 40% within 16 h. During the summer measurement period, changes in the ambient atmospheric water content correlated with changes in the measured effective densities which ranged from approximately 1.0 to 1.5 g x cm(-3). This correlation is potentially due to evaporation of water from particles in the aerodynamic lens. In contrast, in the fall during a Santa Ana meteorological event, ambient particles with a mobility diameter of 450 nm showed three distinct effective densities, each related to a chemically unique particle class. Particles with effective densities of approximately 0.27 g x cm(-3), 0.87 g x cm(-3), and 0.93 g x cm(-3) were composed mostly of elemental carbon, lubricating oil, and aged organic carbon, respectively. It is interesting to contrast the seasonal differences where in the summer, particle density and mass were determined by high amounts of secondary species, whereas in the fall, relatively clean and dry Santa Ana conditions resulted in freshly emitted particles which retained their distinct source chemistries and densities.

Measurement of aerosol effective density by single particle mass spectrometry

“…The methodology for the determination of effective density by DMA-SPAMS has been described in published literature (Spencer et al, 2007;Zelenyuk et al, 2008 (Moffet and Prather, 2005;Moffet et al, 2008). A well fitted linear relationship (R 2 =0.95) is obtained ( Figure 1) and could be applied to make conversion between measured LSS and PSCS for ambient aerosols.…”

“…The retrieved ρ eff was substituted into eq. (3) to get χ; while the ρ eff obtained by DMA-SPAMS is substituted into the following equation get χ v (DeCarlo et al, 2004;Spencer et al, 2007):…”

“…The development and application of SPMS during the past decades improve insight into gas-particle partitioning, heterogeneous reactions, and par-ticle sources (Creamean et al, 2013;Pratt and Prather, 2012). The SPMS measurement has recently been extended to include the particle size, chemical composition, shape, effective density, refractive index, volatility, and hygroscopicity (Buzorius et al, 2002;Pratt and Prather, 2009;Spencer et al, 2007;Zelenyuk et al, 2008). However, the understanding of the properties of single particles in China is still limited.…”

“…It is necessary to note that multiply charged particles may be selected by the DMA, having the same d m but different d va . (Spencer et al, 2007;Zelenyuk et al, 2005Zelenyuk et al, , 2008. This issue could be addressed through the equation: 4), is shown in Figure 5.…”

High-Volume Aerosol Filtration and Mitigation of Inertial Particle Rebound

“…Scanning electron microscope (SEM) images of NaCl and ISO test aerosols, collected on eBMF, are shown in the online supplemental information, Figures S1 and S2, respectively. Particle densities and shape factors for each particle type are given in Table 3 where NaCl data were taken from the work of Spencer et al (2007) and ISO 12103-1 data were taken from Endo et al (1998). Iso-axial sampling probes were used upstream and downstream of the filter section to collect aerosol samples (Baron and Willeke 2001).…”