title: Variability in morphology, hygroscopicity, and optical properties of soot aerosols during atmospheric processing.
abstract: The atmospheric effects of soot aerosols include interference with radiative transfer, visibility impairment, and alteration of cloud formation and are highly sensitive to the manner by which soot is internally mixed with other aerosol constituents. We present experimental studies to show that soot particles acquire a large mass fraction of sulfuric acid during atmospheric aging, considerably altering their properties. Soot particles exposed to subsaturated sulfuric acid vapor exhibit a marked change in morphology, characterized by a decreased mobility-based diameter but an increased fractal dimension and effective density. These particles experience large hygroscopic size and mass growth at subsaturated conditions (<90% relative humidity) and act efficiently as cloud-condensation nuclei. Coating with sulfuric acid and subsequent hygroscopic growth enhance the optical properties of soot aerosols, increasing scattering by approximately 10-fold and absorption by nearly 2-fold at 80% relative humidity relative to fresh particles. In addition, condensation of sulfuric acid is shown to occur at a similar rate on ambient aerosols of various types of a given mobility size, regardless of their chemical compositions and microphysical structures. Representing an important mechanism of atmospheric aging, internal mixing of soot with sulfuric acid has profound implications on visibility, human health, and direct and indirect climate forcing.
authors.affiliation: Department of Atmospheric Sciences, Texas A&M University, College Station, TX 77843, USA.
authors.forename: Renyi
authors.initials: R
authors.lastname: Zhang
authors.forename: Alexei F
authors.initials: AF
authors.lastname: Khalizov
authors.forename: Joakim
authors.initials: J
authors.lastname: Pagels
authors.forename: Dan
authors.initials: D
authors.lastname: Zhang
authors.forename: Huaxin
authors.initials: H
authors.lastname: Xue
authors.forename: Peter H
authors.initials: PH
authors.lastname: McMurry
mesh_terms: D000336:Aerosols; D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry; D000397:Air Pollution; D001272:Atmosphere; D002244:Carbon / Q000032:analysis*; D002621:Chemistry / Q000379:methods; D046529:Microscopy, Electron, Transmission; D008956:Models, Chemical; D055095:Optics and Photonics; D010316:Particle Size; D012107:Research Design; D053260:Soot; D013464:Sulfuric Acids / Q000032:analysis*; D013997:Time Factors
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D053260:Soot; D013464:Sulfuric Acids; D002244:Carbon