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

Abstract

Highlights:1. Morphological transformation occurs via two key complementary and sequential processes, i.e., void filling in the particle and its diameter growth 15 2. A framework was developed for quantifying the state of morphological transformation of soot, i.e., the utilization of material for filling and growth during the condensation processes 3. A method was developed for (i) quantifying the fraction of internal voids and open voids in the soot agglomerate, (ii) deriving the volume equivalent diameter (inclusive of internal voids), and (iii) estimating the in-situ dynamic shape factor 20 Abstract.The morphological transformation of soot particles via condensation of low-volatility materials constitutes a dominant atmospheric process with serious implications for the optical and hygroscopic properties, and atmospheric lifetime of the soot. We consider the morphological transformation of soot agglomerates under the influence of condensation of vapors of sulfuric acid, and/or limonene ozonolysis products. This influence was systematically investigated using a Differential 25Mobility Analyzer-Aerosol Particle Mass Analyzer (DMA-APM) and the Tandem DMA techniques integrated with a laminar flow-tube system. We discovered that the morphology transformation of soot results (in general) from a two-step process, i.e., (i) filling of void space within the agglomerate; (ii) growth of the particle diameter. Initially, the transformation was dominated by the filling process followed by growth, which led to the accumulation of sufficient material that exerted surface forces, which eventually facilitating further filling. The filling of void space was constrained by the initial 30 morphology of the fresh soot as well as the nature and the amount of condensed material. This process continued in several sequential steps until all void space within the soot agglomerate was filled. And then "Growth" of a spherical particle continued as long as vapors condensed on it. We developed a framework for quantifying the microphysical transformation of Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-769 Manuscript under review for journal Atmos. Chem. Phys. Discussion started: 27 October 2017 c Author(s) 2017. CC BY 4.0 License. 2 soot upon the condensation of various materials. This framework used experimental data and the hypothesis of 'ideal sphere growth' and void filling to quantify the distribution of condensed materials in the complementary filling and growth processes. Using this framework, we quantified the percentage of material consumed by these processes at each step of the transformation. We also used the framework to estimate the fraction of internal voids and open voids. This information was then used to derive the volume equivalent diameter of the soot agglomerate containing internal voids and to calculate the in-5 situ dynamic shape factor. The dynamic shape factor estimated based on the traditional assumption (of no internal voids) differed significantly from the value obtained in this study. Internal vo...

More Than Emissions and Chemistry: Fire Size, Dilution, and Background Aerosol Also Greatly Influence Near‐Field Biomass Burning Aerosol Aging

“…Our rationale for using a fixed refractive index is to isolate how the changes in the aerosol size and number affect extinction. The particle extinction is also a function of potentially evolving particle morphology and refractive index in the plume during aging (Pei et al, ), but we do not attempt to address these changes here with justification given in the next paragraph.…”

Calculation of optical properties of light-absorbing carbon with weakly absorbing coating: A model with tunable transition from film-coating to spherical-shell coating

“…The rapid-transition model is further motivated by recent laboratory measurements reported in [31], where the morphological changes of soot particles during the process of condensation of coating material are investigated. They observed that a gradual increase of the amount of coating material first had a negligible effect on the particles' mobility diameter, followed by a sudden sharp increase in diameter.…”

Ice nucleation activities of soot particles internally mixed with sulphuric acid at cirrus cloud conditions

“…2. The coating mechanism is attributed to two pathways, including the direct condensation of supersaturated H2SO4 vapor and the adsorption of small H2SO4 particles formed by homogeneous nucleation (Bambha et al, 2013;Pei et al, 2018). The aerosol sample flow used to generate H2SO4 vapor is heated in an aluminium heating block before going through a flask containing 50 ml pure H2SO4 (Sigma-Aldrich, 95.0-97.0 %) mounted on another aluminium heating block.…”

“…For example, fractal soot agglomerates can be compacted by the condensation of ozonolysis products of α-pinene secondary organic aerosol (SOA) with the bare soot particle serving as a nucleation centre (Saathoff et al, 2003). Khalizov et al (2009) also pointed out that small soot-aggregates gain size growth but larger aggregates show a dramatic size shrinkage due to structure compaction after being exposed to gaseous H2SO4 for more than 10 s. Most recently, Pei et al (2018) investigated the morphological changes of soot particles after H2SO4 or limonene ozonolysis SOA coating, and suggested that the coating material will change soot particle nanostructure by a two-step process. Firstly, external coating material will fill into the voids or pores among soot-aggregates.…”

“…In addition, the coating process can alter soot particle morphology and influence the availability of potential pores for PCF at cirrus cloud conditions. It is reported that external material coating changes the initial soot particle size, particle internal microstructure and surface texture (Saathoff et al, 2003;Khalizov et al, 2009;Pei et al, 2018;Zhang et al, 2020). The size growth caused by considerable addition of coating material is a possible coating effect and the coating material distribution may further modify the soot-aggregate structure.…”