Effects of Coating of Dicarboxylic Acids on the Mass−Mobility Relationship of Soot Particles

Abstract

Atandem differential mobility analyzer (TDMA) and a differential mobility analyzer-aerosol particle mass analyzer (DMA-APM) have been employed to study morphology and hygroscopicity of soot aerosol internally mixed with dicarboxylic acids. The effective densities, fractal dimensions, and dynamic shape factors of soot particles before and after coating with succinic and glutaric acids are determined. Coating of soot with succinic acid results in a significant increase in the particle mobility diameter, mass, and effective density, but these properties recover to their initial values once succinic acid is removed by heating, suggesting that no restructuring of the soot core occurs. This conclusion is also supported from the observation of similar fractal dimensions and dynamic shape factors for fresh and coated/heated soot aggregates. Also, no change is observed when succinic acid-coated aggregates are cycled through elevated relative humidity (5% to 90% to 5% RH) below the succinic acid deliquescence point. When soot is coated with glutaric acid, the particle mass increases, but the mobility diameter shrinks by 10-40%. Cycling the soot aerosol coated with glutaric acid through elevated relative humidity leads to an additional mass increase, indicating that condensed water remains within the coating even at low RH. The fractal dimension of soot particles increases after coating and remains high when glutaric acid is removed by heating. The dynamic shape factor of glutaric acid-coated and heated soot is significantly lower than that of fresh soot, suggesting a significant restructuring of the soot agglomerates by glutaric acid. The results imply that internal mixing of soot aerosol during atmospheric aging leads to changes in hygroscopicity, morphology, and effective density, which likely modify their effects on direct and indirect climate forcing and deposition in the human respiratory system.

Interpretation of Secondary Organic Aerosol Formation from Diesel Exhaust Photooxidation in an Environmental Chamber

“…The APM is located upstream of the SMPS for improved time resolution (∼1 min) over the more common configuration of the differential mobility analyzer (DMA)-APM (McMurry et al 2002;Khalizov et al 2009;Xue et al 2009). A detailed description of the APM-SMPS system and data algorithms are described elsewhere (Malloy et al 2009).…”

“…In this study, the APM setting was programmed to select 3-5 different particle masses (typically in 20 min) to obtain particle density as a function of particle mass. Fractal-like dimension was obtained by fitting the effective density versus size relationship into a power function (Park et al 2003;Xue et al 2009): where ρ eff is the effective density of particles, C is a constant, d m is the mobility diameter of particles, and D f is the fractal-like dimension.…”

Markedly enhanced absorption and direct radiative forcing of black carbon under polluted urban environments

“…BC aging leads to a large variation in the particle morphology, depicted in the evolutions of the effective density (ρ eff ) and dynamic shape factor (DSF) ( , and 0.25 g·cm −3 and 2.2, 2.5, and 2.8, respectively, indicating fractal aggregates with chain-like branches (10,11,(20)(21)(22) and a more fractal morphology for a larger size. Our estimated fractal dimension of 2.25 for fresh BC particles is similar to those in the previous studies (13,22,23).…”

Key role of organic carbon in the sunlight-enhanced atmospheric aging of soot by O2

“…Zhang and colleagues (50,51) found that soot can reduce the photolysis frequencies of O 3 and NO 2 by absorbing sunlight, leading to a reduction in the concentration of HOx and O 3 . However, the optical properties of soot greatly depend upon its morphology, composition, and structure (21,22,52,53). Thus modification of soot during the photochemical aging process by O 2 may significantly alter its optical properties, resulting in changes in the effects of soot on the photochemistry of some atmospheric oxidants.…”