Influence of the dry aerosol particle size distribution and morphology on the cloud condensation nuclei activation. An experimental and theoretical investigation

Abstract

Combustion and other high-temperature processes frequently result in the emission of aerosols in the form of polydisperse fractal-like aggregates made of condensedphase nanoparticles (soot for instance). If certain conditions are met, the emitted aerosol particles are known to evolve into important cloud condensation nuclei (CCN) in the atmosphere. In this work, the hygroscopic parameter κ of complex morphology aggregates is calculated from the supersaturation-dependent activated fraction F a = F a (SS) in the frame of κ-Köhler theory. The particle size distribution is approximated with the morphology-corrected volume equivalent diameter calculated from the electrical mobility diameter by taking into account the diameter of the primary particle and the fractal dimension of the aggregate experimentally obtained from transmission electron microscopy measurements. Activation experiments are performed in water supersaturation conditions using a commercial CCN-100 condensation nuclei counter. The model is tested in closeto-ideal conditions of size-selected, isolated spherical particles (ammonium sulfate nanoparticles dispersed in nitrogen), then with complex polydisperse fractal-like aggregates (soot particles activated by exposure to ozone with κ as low as 5 × 10 −5 ) that represent realistic anthropogenic emissions in the atmosphere.

The Mechanical Alignment of Dust (MAD) I: On the spin-up process of fractal grains by a gas-dust drift

“…Kozasa et al 1992;Shen et al 2008). However, laboratory data suggests that a plethora of different materials form fractal aggregates composed of monomers with variable sizes (Chakrabarty et al 2007;Slobodrian et al 2011;Kandilian et al 2015;Baric et al 2018;Kelesidis et al 2018;Salameh et al 2017;Wu et al 2020;Zhang et al 2020;Kim et al 2021). The size distribution of the monomers itself may follow a log-normal distribution…”

Hydrophilic properties of soot particles exposed to OH radicals: A possible new mechanism involved in the contrail formation

“…In order to determine the hygroscopicity parameter , an extension of -Köhler theory [16] that takes into account the effect of the dry particle size distribution [25], the complex morphology of soot [17] and a distribution of  values [26] is used. This model [16] is applied here to fit the activation curves ( §4.2.1).…”

“…Being soot particles fractal-like objects, it is necessary to consider an equivalent diameter in alternative to d p . A morphology-corrected volume equivalent diameter d ve can be calculated [17,27] from the electrical mobility d m , the diameter of primary particles d pp , the number of primary particles per aggregate N pp and the aggregate fractal dimension D f (see Table 1), following the conversion model proposed by Yon et al [27]. The only two free parameters of the fitting are the geometric mean and standard deviation of the  distribution  ,geo and   , geo .…”

“…3b shows p() of kerosene soot measured at different OH exposure. According to the model sensitivity study [17],  ,geo is set as a free parameter while  ,geo = 1.6 is kept fixed and is calculated from the average of the four curves at higher exposure (the curves that reach the plateau at F a = 1 allow for more accurate fits). Fig.…”

“…For different OH exposures, soot activation is measured in water supersaturation conditions using a commercial cloud condensation nuclei counter (CCNc). According to -Köhler theory [16], the hygroscopicity parameter  is calculated following a theoretical approach that we recently proposed [17]. In the final section of this work, the experimental results are used to determine if the soot aging in the turbine of an aeronautical engine would be sufficient to activate the emitted soot particles.…”