title: A new real-time method for determining particles' sphericity and density: application to secondary organic aerosol formed by ozonolysis of alpha-pinene.
abstract: Particle volumes are most often obtained by measuring particle mobility size distributions and assuming that the particles are spherical. Particle volumes are then converted to mass loads by using particle densities that are commonly estimated from measured mobility and vacuum aerodynamic diameters, assuming that the particles are spherical. For aspherical particles, these assumptions can introduce significant errors. We present in this work a new method that can be applied to any particle system to determine in real time whether the particles are spherical or not. We use our second-generation single particle mass spectrometer (SPLAT II) to measure with extremely high precision the vacuum aerodynamic size distributions of particles that are classified by differential mobility analyzer and demonstrate that the line shape of these vacuum aerodynamic size distributions provide a way to unambiguously distinguish between spherical and aspherical particles. Moreover, the very same experimental system is used to obtain the size, density, composition, and dynamic shape factors of individual particles. We present an application of this method to secondary organic aerosols that are formed as a result of ozonolysis of alpha-pinene in the presence and absence of an OH scavenger and find these particles to be spherical with densities of 1.198 +/- 0.004 and 1.213 +/- 0.003 g cm(-3), respectively.
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA. alla.zelenyuk@pnl.gov
authors.forename: Alla
authors.initials: A
authors.lastname: Zelenyuk
authors.forename: Juan
authors.initials: J
authors.lastname: Yang
authors.forename: Chen
authors.initials: C
authors.lastname: Song
authors.forename: Rahul A
authors.initials: RA
authors.lastname: Zaveri
authors.forename: Dan
authors.initials: D
authors.lastname: Imre
mesh_terms: D000336:Aerosols / Q000737:chemistry*; D000081008:Bicyclic Monoterpenes; D004051:Diethylhexyl Phthalate / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods*; D039821:Monoterpenes / Q000737:chemistry*; D010126:Ozone / Q000737:chemistry*; D010316:Particle Size; D011137:Polystyrenes / Q000737:chemistry; D011721:Pyrenes / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D013997:Time Factors; D014618:Vacuum
chemical_list: D000336:Aerosols; D000081008:Bicyclic Monoterpenes; D039821:Monoterpenes; D011137:Polystyrenes; D011721:Pyrenes; D012965:Sodium Chloride; D010126:Ozone; C024075:styrofoam; C030984:pyrene; D004051:Diethylhexyl Phthalate; C005451:alpha-pinene