Detailed heterogeneous oxidation of soot surfaces in a particle-resolved aerosol model

Abstract

Abstract.Using the particle-resolved aerosol model PartMC-MOSAIC, we simulate the heterogeneous oxidation of a monolayer of polycyclic aromatic hydrocarbons (PAHs) on soot particles in an urban atmosphere. We focus on the interaction of the major atmospheric oxidants (O 3 , NO 2 , OH, and NO 3 ) with PAHs and include competitive co-adsorption of water vapour for a range of atmospheric conditions. For the first time detailed heterogeneous chemistry based on the Pöschl-Rudich-Ammann (PRA) framework is modelled on soot particles with a realistic size distribution and a continuous range of chemical ages. We find PAH half-lives, τ 1/2 , on the order of seconds during the night, when the PAHs are rapidly oxidised by the gas-surface reaction with NO 3 . During the day, τ 1/2 is on the order of minutes and determined mostly by the surface layer reaction of PAHs with adsorbed O 3 . Such short half-lives of surface-bound PAHs may lead to efficient conversion of hydrophobic soot into more hygroscopic particles, thus increasing the particles' aerosol-cloud interaction potential. Despite its high reactivity OH appears to have a negligible effect on PAH degradation which can be explained by its very low concentration in the atmosphere. An increase of relative humidity (RH) from 30 % to 80 % increases PAH half-lives by up to 50 % for daytime degradation and by up to 100 % or more for nighttime degradation. Uptake coefficients, averaged over the particle population, are found to be relatively constant over time for O 3 (∼ 2 × 10 −7 to ∼ 2×10 −6 ) and NO 2 (∼ 5×10 −6 to ∼ 10 −5 ) at the different levels of NO x emissions and RH considered in this study. In contrast, those for OH and NO 3 depend strongly on the surface concentration of PAHs. We do not find a significantCorrespondence to: N. Riemer (nriemer@illinois.edu) influence of heterogeneous reactions on soot particles on the gas phase composition. The derived half-lives of surfacebound PAHs and the time and particle population averaged uptake coefficients for O 3 and NO 2 presented in this paper can be used as parameterisations for the treatment of heterogeneous chemistry in large-scale atmospheric chemistry models.

Modeling the evolution of aerosol particles in a ship plume using PartMC-MOSAIC

“…This model explicitly resolves the composition of individual particles in a given aerosol population and is therefore uniquely suited to investigate the evolution of particle mixing states and the associated particle properties. PartMC-MOSAIC has been used for detailed studies on the particle level, for example to derive aging time-scales of black carbon aerosol (Riemer et al, 2010), to investigate the heterogeneous oxidation of soot surfaces (Kaiser et al, 2011), to quantify the impacts of black carbon mixing state on black carbon nucleation scavenging (Ching et al, 2012), and to explore the sensitivity of cloud condensation nuclei activity to particle characteristics at emission (Fierce et al, 2013). It was also used as a modeling tool to explain the diurnal variations of aerosol hygroscopicity and the mixing state of light-absorbing carbonaceous material in the North China Plain (Liu et al, 2011;Ma et al, 2012).…”

Kinetic multi-layer model of gas-particle interactions in aerosols and clouds (KM-GAP): linking condensation, evaporation and chemical reactions of organics, oxidants and water

“…Using K2-SURF Shiraiwa et al (2011b) showed that long-lived reactive oxygen intermediates are formed in the reaction of ozone with aerosol particles. Springmann et al (2009) and Kaiser et al (2011) demonstrated the applicability and usefulness of the PRA framework in an urban plume box model of the degradation of benzo [a]pyrene on soot by ozone and nitrogen dioxide. Pfrang et al (2010) developed a kinetic double-layer model coupling aerosol surface and bulk chemistry (K2-SUB), in which mass transport and chemical reactions in the bulk are not explicitly resolved but represented by a reacto-diffusive flux analogous to traditional resistormodel formulations.…”

Review response

“…The synthesis of monofunctional alkyl nitrates can be performed via several methods (Boschan et al, 1955), including nitration of alkyl halides with silver nitrate, direct nitration of alcohols or alkanes with nitric acid (Luxenhofer et al, 1996;Woidich et al, 1999), or treatment of alcohols with dinitrogen pentoxide (Kames et al, 1993). Techniques for the synthesis of multifunctional nitrates (in particular, hydroxynitrates) have been described in previous reports (Muthuramu et al, 1993;Kastler and Ballschmiter, 1998;Werner et al, 1999;Treves et al, 2000).…”