Effective Density and Mixing State of Aerosol Particles in a Near-Traffic Urban Environment

Abstract

In urban environments, airborne particles are continuously emitted, followed by atmospheric aging. Also, particles emitted elsewhere, transported by winds, contribute to the urban aerosol. We studied the effective density (mass-mobility relationship) and mixing state with respect to the density of particles in central Copenhagen, in wintertime. The results are related to particle origin, morphology, and aging. Using a differential mobility analyzer-aerosol particle mass analyzer (DMA-APM), we determined that particles in the diameter range of 50-400 nm were of two groups: porous soot aggregates and more dense particles. Both groups were present at each size in varying proportions. Two types of temporal variability in the relative number fraction of the two groups were found: soot correlated with intense traffic in a diel pattern and dense particles increased during episodes with long-range transport from polluted continental areas. The effective density of each group was relatively stable over time, especially of the soot aggregates, which had effective densities similar to those observed in laboratory studies of fresh diesel exhaust emissions. When heated to 300 °C, the soot aggregate volatile mass fraction was ∼10%. For the dense particles, the volatile mass fraction varied from ∼80% to nearly 100%.

Morphological transformation of soot: investigation of microphysical processes during the condensation of sulfuric acid and limonene ozonolysis product vapors

“…Similarly, Rissler et al (2013) obtained, via TEM analysis, values of 24, 27, 28, 11, and 13 nm, for particles (geometric mean diameter: 50 nm) associated with a heavy-duty transient diesel engine, heavy-duty idling diesel engine, light-duty idling diesel engine, candle, and propane flame soot, respectively. Our d pp (i.e., 28 nm) is similar to that obtained from field measurements performed by Rissler et al (2014), indicating that the soot agglomerates considered in this study are similar to real-world soot particles. According to the Sorensen model, the d pp determines the void fraction in 25 the agglomerate.…”

Morphological transformation of soot: investigation of microphysical processes during the condensation of sulfuric acid and limonene ozonolysis product vapors

“…(12) and (13) (2013) obtained, via TEM analysis, values of 24, 27, 28, 11, and 13 nm, for particles (geometric mean diameter: 50 nm) associated with a heavy-duty transient diesel engine, heavy-duty idling diesel engine, light-duty idling diesel engine, candle, and propane flame soot, respectively. Our d pp (i.e., 28 nm) is similar to that obtained from field measurements performed by Rissler et al (2014), indicating that the soot aggregates considered in this study are similar to realworld soot particles. According to the Sorensen model, the d pp determines the void fraction in the aggregate.…”

A Set-up for Respiratory Tract Deposition Efficiency Measurements (15-5000 nm) and First Results for a Group of Children and Adults

“…For the purpose of illustrating the effect of individual variability in DF on TDF and Drate, we applied the measured DF to two model aerosols. The model aerosols had particle size distributions identical to those found at: (i) a busy street in central Copenhagen, Denmark (referred to as Model Aerosol 1), and (ii) a rural site in Scania, in southern Sweden (referred to as Model Aerosol 2), see Rissler et al (2014). The aerosol found at the busy street was dominated, at least with respect to number, by ultrafine or nano particles.…”

“…When converted to particle volume (or mass) size distributions, the particles found at the busy street were described by a unimodal size distribution with a GMD of 620 nm (σ g : 2.6) and the rural site particles by a distribution with a GMD of 304 nm (σ g : 1.6). More information about the aerosols can be found in Rissler et al (2014).…”