Abstract
Abstract. Ambient measurements combined with theoretical simulations have shown evidence that the tropospheric degradation end-products of Freon alternatives, trifluoroacetic acid (TFA), one of the most important and abundant atmospheric organic substances, can enhance the nucleation process based on sulfuric acid (SA) and dimethylamine (DMA) in urban environments. However, TFA is widespread all over the world under different atmospheric conditions, such as temperature and nucleation precursor concentration, which are the most important factors potentially influencing the atmospheric nucleation process and thus inducing different nucleation mechanisms. Herein, using the density functional theory combined with the Atmospheric Cluster Dynamics Code, the influence of temperature and nucleation precursor concentrations on the role of TFA in the SA–DMA nucleation has been investigated. The results indicate that the growth trends of clusters involving TFA can increase with the decrease in temperature. The enhancement on particle formation rate by TFA and the contributions of the SA–DMA–TFA cluster to the cluster formation pathways can be up to 227-fold and 95 %, respectively, at relatively low temperature, low SA concentration, high TFA concentration, and high DMA concentration, such as in winter, at the relatively high atmospheric boundary layer, or in megacities far away from industrial sources of sulfur-containing pollutants. These results provide the perspective of the realistic role of TFA in different atmospheric environments, revealing the potential influence of the tropospheric degradation of Freon alternatives under a wide range of atmospheric conditions.
Highlights
Atmospheric aerosols have significant adverse impacts on climate and human health (Kulmala et al, 2007; Stevens and Feingold, 2009)
The present study shows the influence of atmospheric conditions on the role of trifluoroacetic acid (TFA) in sulfuric acid (SA)–DMA nucleation by the combination of high-level quantum-chemical calculations with the Atmospheric Cluster Dynamics Code (ACDC) simulations in the typical ranges of atmospheric temperature and nucleation precursor concentration
The enhancement on particle formation rate by TFA and the contributions of the SA–DMA– TFA cluster formation pathway to the main cluster pathways increase with the decrease in temperature, the increase in [DMA] and [TFA], and the decrease in [SA]
Summary
Atmospheric aerosols have significant adverse impacts on climate and human health (Kulmala et al, 2007; Stevens and Feingold, 2009). Understanding the nucleation mechanisms and compositions of nucleation precursors well can help to predict the impacts of NPF events and further provide theoretical clues to reducing the severe atmospheric aerosol pollution, haze. Sulfuric acid has been well recognized as the key nucleation precursor (Doyle, 1961; Kulmala et al, 1995, 2013; Berndt et al, 2005). The sulfuric acid (SA) and dimethylamine (DMA) nucleation mechanism has been observed in various places around the world (Yao et al, 2018; Deng et al, 2020; Brean et al, 2020), there are still a lot of species observed in the atmosphere but not fully assigned molecular formulas because of their chemical complexity. Other species that can potentially enhance the NPF rates and the corresponding nucleation mechanism should still be further explored
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