Abstract
Abstract. Typical tropospheric temperatures render possible phase states of amorphous organic aerosol (OA) particles of solid, semisolid, and liquid. This will affect the multiphase oxidation kinetics involving the organic condensed-phase and gaseous oxidants and radicals. To quantify this effect, we determined the reactive uptake coefficients (γ) of O3, NO3, and OH by substrate films composed of single and binary OA surrogate species under dry conditions for temperatures from 213 to 313 K. A temperature-controlled coated-wall flow reactor coupled to a chemical ionization mass spectrometer was applied to determine γ with consideration of gas diffusion transport limitation and gas flow entrance effects, which can impact heterogeneous reaction kinetics. The phase state of the organic substrates was probed via the poke-flow technique, allowing the estimation of the substrates' glass transition temperatures. γ values for O3 and OH uptake to a canola oil substrate, NO3 uptake to a levoglucosan and a levoglucosan / xylitol substrate, and OH uptake to a glucose and glucose / 1,2,6-hexanetriol substrate have been determined as a function of temperature. We observed the greatest changes in γ with temperature for substrates that experienced the largest changes in viscosity as a result of a solid-to-liquid phase transition. Organic substrates that maintain a semisolid or solid phase state and as such a relatively higher viscosity do not display large variations in heterogeneous reactivity. From 213 to 293 K, γ values of O3 with canola oil, of NO3 with a levoglucosan / xylitol mixture, and of OH with a glucose / 1,2,6-hexanetriol mixture and canola oil, increase by about a factor of 34, 3, 2, and 5, respectively, due to a solid-to-liquid phase transition of the substrate. These results demonstrate that the surface and bulk lifetime of the OA surrogate species can significantly increase due to the slowed heterogeneous kinetics when OA species are solid or highly viscous in the middle and upper troposphere. This experimental study will further our understanding of the chemical evolution of OA particles with subsequent important consequences for source apportionment, air quality, and climate.
Highlights
IntroductionOrganic aerosol (OA) particles are ubiquitous and can represent 20 %–90 % of the mass fraction of the submicron aerosol (particles ≤ 1 μm in diameter) in the atmosphere
Organic aerosol (OA) particles are ubiquitous and can represent 20 %–90 % of the mass fraction of the submicron aerosol in the atmosphere
The phase states of the organic substrate films were examined using the poke-flow technique, allowing for an estimation of Tg and substrate flow characteristics to constrain the magnitude of the substrate viscosity at different temperatures using the VTF equation
Summary
Organic aerosol (OA) particles are ubiquitous and can represent 20 %–90 % of the mass fraction of the submicron aerosol (particles ≤ 1 μm in diameter) in the atmosphere. The significance of OA has long been established, influencing air quality, human health, cloud formation processes, and the radiative budget, on a regional and global scale, and climate (Hallquist et al, 2009; Jimenez et al, 2009; Seinfeld and Pandis, 2016; Stocker et al, 2013; Knopf et al, 2018; Abbatt et al, 2019; Shiraiwa et al, 2017b; Kanakidou et al, 2005; Pachauri et al, 2014; Pöschl and Shiraiwa, 2015) Characterizing these impacts crucially depends on our ability to determine and quantify aerosol sources and strengths (Bai et al, 2013; Robinson et al, 2006; McFiggans et al, 2019; Hopke, 2016) and to understand the physical and chemical transformation of aerosol particles during atmospheric transport by multiphase chemical processes (George and Abbatt, 2010; Rudich et al, 2007; Laskin et al, 2015; Springmann et al, 2009; Kaiser et al, 2011; Ervens et al, 2011; Zhou et al, 2019; Moise et al, 2015). Li et al.: Heterogeneous oxidation of amorphous organic aerosol surrogates their chemical lifetime, optical properties, and ice nucleating ability (Jimenez et al, 2009; Kroll et al, 2015; Katrib et al, 2005b; Knopf et al, 2018; Slade et al, 2017; Robinson et al, 2007; Shiraiwa et al, 2012, 2017a; Moise et al, 2015; Murray et al, 2010; Wang et al, 2012)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
