Detailed heterogeneous chemistry in an urban plume box model: reversible co-adsorption of O<sub>3</sub>, NO<sub>2</sub>, and H<sub>2</sub>O on soot coated with benzo[a]pyrene

Abstract

Abstract. This study assesses in detail the effects of heterogeneous chemistry on the particle surface and gas-phase composition by modeling the reversible co-adsorption of O3, NO2, and H2O on soot coated with benzo[a]pyrene (BaP) for an urban plume scenario over a period of five days. By coupling the Pöschl-Rudich-Ammann (PRA) kinetic framework for aerosols (Pöschl et al., 2007) to a box model version of the gas phase mechanism RADM2, we are able to track individual concentrations of gas-phase and surface species over the course of several days. The flux-based PRA formulation takes into account changes in the uptake kinetics due to changes in the chemical gas-phase and particle surface compositions. This dynamic uptake coefficient approach is employed for the first time in a broader atmospheric context of an urban plume scenario. Our model scenarios include one to three adsorbents and three to five coupled surface reactions. The results show a variation of the O3 and NO2 uptake coefficients of more than five orders of magnitude over the course of simulation time and a decrease in the uptake coefficients in the various scenarios by more than three orders of magnitude within the first six hours. Thereafter, periodic peaks of the uptake coefficients follow the diurnal cycle of gas-phase O3-NOx reactions. Physisorption of water vapor delays the half-life of the coating substance BaP by up to a factor of seven by permanently occupying ~75% of the soot surface. Soot emissions modeled by replenishing reactive surface sites lead to maximum gas-phase O3 depletions of 41 ppbv for an hourly and 7.8 ppbv for a six-hourly replenishment cycle. This conceptual study highlights the interdependence of co-adsorbing species and their non-linear gas-phase feedback. It yields further insight into the atmospheric importance of the chemical oxidation of particles and guides future modeling and experimental investigations of the heterogeneous chemistry and chemical aging of aerosols.

Chemical aging of single and multicomponent biomass burning aerosol surrogate particles by OH: implications for cloud condensation nucleus activity

“…At RH > 15 %, MNC is less reactive with OH, exhibiting γ < 0.07 due to competitive co-adsorption of water and OH (Slade and Knopf, 2014). Similar suppressions in gas uptake, due to competitive adsorption processes, have been observed in the case of OH and NO 3 uptake by BBA surrogate films (Slade and Knopf, 2013;Knopf et al, 2011), O 3 uptake by benzo [a]pyrene in the presence of water vapor (Pöschl et al, 2001), and O 3 and NO 2 uptake by benzo[a]pyrenecoated soot (Springmann et al, 2009;Kaiser et al, 2011 The presence of higher [O 3 ] may further decrease the OH reactivity of OA (Renbaum and Smith, 2011). Under the applied experimental conditions, the multiphase reaction kinetics involving highly viscous organic material are likely limited by surface-bulk exchange (Arangio et al, 2015;Slade and Knopf, 2014).…”

Heterogeneous ice nucleation and water uptake by field‐collected atmospheric particles below 273 K

“…When exposed to low temperatures, aqueous organic particles can form glasses which are disordered amorphous solids [ Murray , 2008; Zobrist et al , 2008, 2011; Koop et al , 2011]. During transport, aerosol particles can undergo various atmospheric aging processes including, but not limited to: (1) condensation of SOA due to photochemical processing of VOCs [ Seinfeld and Pandis , 1998; Kanakidou et al , 2005], (2) heterogeneous oxidation by atmospheric trace gases such as O 3 , NO 3 , and OH which can lead to the formation of hydrophilic functional groups on the particle surfaces [ Akhter et al , 1985; Smith et al , 1988; Chughtai et al , 1991; Kanakidou et al , 2005; Zuberi et al , 2005; Knopf et al , 2006; Rudich et al , 2007; Daly and Horn , 2009; Springmann et al , 2009; George and Abbatt , 2010; Knopf et al , 2011a; Kaiser et al , 2011], and (3), condensation of hydrophilic material such as inorganic acids, i.e., H 2 SO 4 and HNO 3 [ Jang et al , 2002; Riemer et al , 2004; George and Abbatt , 2010]. Modifications of surface chemistry can affect the particles' hygroscopicities and ice nucleation efficiencies.…”

Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2-SURF): Degradation of polycyclic aromatic hydrocarbons exposed to O&lt;sub&gt;3&lt;/sub&gt;, NO&lt;sub&gt;2&lt;/sub&gt;, H&lt;sub&gt;2&lt;/sub&gt;O, OH and NO&lt;sub&gt;3&lt;/sub&gt;

“…Recently, Springmann et al (2009) have demonstrated the applicability and usefulness of the PRA framework Pöschl et al, 2007) for atmospheric modeling of the degradation of benzo[a]pyrene on soot by ozone and nitrogen dioxide. In this study we show that the PRA model approach can be efficiently extended to other PAHs and photo-oxidants.…”