Combined theoretical and experimental investigations of peroxy radical uptake on organic aerosols

Antoine Roose (1, 2) , Sébastien Dusanter (1) , Céline Toubin (2) , Denis Duflot (2) , Véronique Riffault (1)

1 CERI EE - IMT Nord Europe - Centre for Energy and Environment
2 PCMT - Physico-Chimie Moléculaire Théorique

Significant uncertainties are still associated to chemical reaction mechanisms used in atmospheric models, in particular for ROx radicals (OH, HO₂, RO₂). Recent measurements of radicals in forested areas characterized by low NO_x (NO₂, NO) concentrations indicate that models can significantly overestimate peroxy radical concentrations.^1,2 These results question the ability of models to correctly simulate the oxidative capacity of the troposphere since peroxy radicals are a main source of the hydroxyl radical (OH), one of the most important oxidative species in the atmosphere.3 One possible explanation is the occurrence of heterogeneous processes (uptake of radicals) on the surface of aerosols that are either misrepresented or not included in models. While recent studies have reported uptake coefficients of HO₂ on different types of aerosols, uptakes of RO₂ radicals have yet to be investigated and the process is not completely understood yet. Both theoretical and experimental tools have been used to study HO₂ uptake on organic aerosols. A PERCA (Peroxy Radical Chemical Amplifier) instrument capable of measuring HO₂ and RO₂ radical concentrations has been coupled to an aerosol flow tube to quantify HO₂ uptakes on glutaric acid aerosols at different relative humidities. In complement to this experimental work, molecular dynamics combined with ab-initio calculations has been used to model a nanometer size aerosol particle and the sticking process of HO₂ on the organic particle. These theoretical calculations provide insight into the uptake process at the molecular scale. In this presentation, we will emphasize the advantage of using a dual experimental/theoretical approach to investigate the uptake of radical species on atmospheric aerosols. This work is supported by the CaPPA project (Chemical and Physical Properties of the Atmosphere), funded by the French National Research Agency (ANR) through the PIA (Programme d’investissement d’avenir) and by the regional council “Hauts-de-France”. The authors also thank CPER Climibio and FEDER for their financial support. Calculations were performed using HPC resources from GENCI-TGCC (Grant 2017-A0010806820). References [1] P. T. Griffith et al., Atmos. Chem. Phys. 13, 5403 (2013) [2] J. Mao et al., Atmos. Chem. Phys. 12, 8009 (2012) [3] D. Stone et al., Chem. Soc. Rev. 41, 6348 (2012)

Domaines: Chimie théorique et/ou physique; Chimie-Physique [physics.chem-ph]

Antoine Roose, Sébastien Dusanter, Céline Toubin, Denis Duflot, Véronique Riffault. Combined theoretical and experimental investigations of peroxy radical uptake on organic aerosols. EGU General Assembly 2019, Apr 2019, Vienna, Austria. ⟨hal-02161228⟩