Effects of oligomerization and decomposition on the nanoparticle growth: a model study

Arto Heitto,Felipe Lopez-Hilfiker,Taina Yli-Juuti,Kari Lehtinen,Markku Kulmala,Joel A Thornton,Tuukka Petäjä

doi:10.5194/acp-22-155-2022

Abstract

Abstract. The rate at which freshly formed secondary aerosol particles grow is an important factor in determining their climate impacts. The growth rate of atmospheric nanoparticles may be affected by particle-phase oligomerization and decomposition of condensing organic molecules. We used the Model for Oligomerization and Decomposition in Nanoparticle Growth (MODNAG) to investigate the potential atmospheric significance of these effects. This was done by conducting multiple simulations with varying reaction-related parameters (volatilities of the involved compounds and reaction rates) using both artificial and ambient measured gas-phase concentrations of organic vapors to define the condensing vapors. While our study does not aim at providing information on any specific reaction, our results indicate that particle-phase reactions have significant potential to affect the nanoparticle growth. In simulations in which one-third of a volatility basis set bin was allowed to go through particle-phase reactions, the maximum increase in growth rates was 71 % and the decrease 26 % compared to the base case in which no particle-phase reactions were assumed to take place. These results highlight the importance of investigating and increasing our understanding of particle-phase reactions.

Highlights

Aerosols are ubiquitous in the atmosphere, and they affect our climate in multiple ways
The three condensing groups (I–III) all include seven organic compounds which are defined by their saturation concentration (C∗) using volatility basis set (VBS; Donahue et al, 2011), in which the volatility bins range from C∗ = 10−4 μg m−3 to C∗ = 102 μg m−3
A wide range of model simulations were conducted to study the effect of particle-phase oligomerization and decomposition on the nanoparticle growth

Summary

Introduction

Aerosols are ubiquitous in the atmosphere, and they affect our climate in multiple ways They can affect the radiative forcing by reflecting, refracting and absorbing sunlight and indirectly by acting as cloud condensation nuclei (CCN) and forming clouds (Boucher et al, 2013). For an aerosol particle to act as CCN, it needs to be large enough in size, at least some tens of nanometers in diameter (Pierce and Adams, 2007; Reddington et al, 2017). This can be, on one hand, a limiting factor for climate impacts of small primary aerosols as Aitken-mode-sized primary particles such as soot particles are quite often non-hygroscopic, which hinders their activation as CCN (e.g., Zhang et al, 2008). Regardless, it is estimated that approximately half of the particles acting as CCN are formed in the atmosphere by nucleation from atmospheric gases (Merikanto et al, 2009; Paramonov et al, 2015)

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