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This study assesses in detail the effects of heterogeneous chemistryon the particle surface and gas-phase composition by modeling thereversible co-adsorption of O3, NO2, and H2O on soot coatedwith benzo[a]pyrene (BaP) for an urban plume scenario over a periodof five days. By coupling the Pöschl-Rudich-Ammann (PRA) kineticframework for aerosols (Pöschl et al., 2007) to a boxmodel version of the gas phase mechanism RADM2, we are able to trackindividual concentrations of gas-phase and surface species over thecourse of several days. The flux-based PRA formulation takes intoaccount changes in the uptake kinetics due to changes in thechemical gas-phase and particle surface compositions. This dynamicuptake coefficient approach is employed for the first time in abroader atmospheric context of an urban plume scenario. Our model scenarios include one to three adsorbents andthree to five coupled surface reactions. The results show avariation of the O3 and NO2 uptake coefficients of more thanfive orders of magnitude over the course of the simulation time and adecrease in the uptake coefficients in the various scenarios by morethan three orders of magnitude within the first six hours.Thereafter, periodic peaks of the uptake coefficients follow thediurnal cycle of gas-phase O3-NOx reactions. Physisorption ofwater vapor reduces the half-life of the coating substance BaPby up to a factor of seven by permanently occupying ~75% ofthe soot surface. Soot emissions modeled by replenishingreactive surface sites lead to maximum gas-phase O3 depletions of41 ppbv and 7.8 ppbv for an hourly and six-hourly replenishmentcycle, respectively. This conceptual study highlights theinterdependence of co-adsorbing species and their non-lineargas-phase feedback. It yields further insight into theatmospheric importance of the chemical oxidation of particles andemphasizes the necessity to implement detailed heterogeneouskinetics in future modeling studies

atmospheric chemistry and physics

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