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1. The driving effects of common atmospheric molecules for formation of clusters: the case of sulfuric acid, formic acid, hydrochloric acid, ammonia, and dimethylamine

   https://doi.org/10.1039/D3EA00087G  

   Longsworth, Olivia M.; Bready, Conor J.; Shields, George C. (September 2023, Environmental Science: Atmospheres)

   One of the main sources of uncertainty for understanding global warming is understanding the formation of larger secondary aerosols. 

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2. The driving effects of common atmospheric molecules for formation of prenucleation clusters: the case of sulfuric acid, formic acid, nitric acid, ammonia, and dimethyl amine

   https://doi.org/10.1039/D2EA00087C  

   Bready, Conor J.; Fowler, Vance R.; Juechter, Leah A.; Kurfman, Luke A.; Mazaleski, Grace E.; Shields, George C. (October 2022, Environmental Science: Atmospheres)

   How secondary aerosols form is critical as aerosols' impact on Earth's climate is one of the main sources of uncertainty for understanding global warming. The beginning stages for formation of prenucleation complexes, that lead to larger aerosols, are difficult to decipher experimentally. We present a computational chemistry study of the interactions between three different acid molecules and two different bases. By combining a comprehensive search routine covering many thousands of configurations at the semiempirical level with high level quantum chemical calculations of approximately 1000 clusters for every possible combination of clusters containing a sulfuric acid molecule, a formic acid molecule, a nitric acid molecule, an ammonia molecule, a dimethylamine molecule, and 0–5 water molecules, we have completed an exhaustive search of the DLPNO-CCSD(T)/CBS//ωB97X-D/6-31++G** Gibbs free energy surface for this system. We find that the detailed geometries of each minimum free energy cluster are often more important than traditional acid or base strength. Addition of a water molecule to a dry cluster can enhance stabilization, and we find that the (SA)(NA)(A)(DMA)(W) cluster has special stability. Equilibrium calculations of SA, FA, NA, A, DMA, and water using our quantum chemical Δ G ° values for cluster formation and realistic estimates of the concentrations of these monomers in the atmosphere reveals that nitric acid can drive early stages of particle formation just as efficiently as sulfuric acid. Our results lead us to believe that particle formation in the atmosphere results from the combination of many different molecules that are able to form highly stable complexes with acid molecules such as SA, NA, and FA. 

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3. Substantial contribution of transported emissions to organic aerosol in Beijing

   https://doi.org/10.1038/s41561-024-01493-3  

   Daellenbach, Kaspar R; Cai, Jing; Hakala, Simo; Dada, Lubna; Yan, Chao; Du, Wei; Yao, Lei; Zheng, Feixue; Ma, Jialiang; Ungeheuer, Florian; et al (August 2024, Nature Geoscience)

   Abstract Haze in Beijing is linked to atmospherically formed secondary organic aerosol, which has been shown to be particularly harmful to human health. However, the sources and formation pathways of these secondary aerosols remain largely unknown, hindering effective pollution mitigation. Here we have quantified the sources of organic aerosol via direct near-molecular observations in central Beijing. In winter, organic aerosol pollution arises mainly from fresh solid-fuel emissions and secondary organic aerosols originating from both solid-fuel combustion and aqueous processes, probably involving multiphase chemistry with aromatic compounds. The most severe haze is linked to secondary organic aerosols originating from solid-fuel combustion, transported from the Beijing–Tianjing–Hebei Plain and rural mountainous areas west of Beijing. In summer, the increased fraction of secondary organic aerosol is dominated by aromatic emissions from the Xi’an–Shanghai–Beijing region, while the contribution of biogenic emissions remains relatively small. Overall, we identify the main sources of secondary organic aerosol affecting Beijing, which clearly extend beyond the local emissions in Beijing. Our results suggest that targeting key organic precursor emission sectors regionally may be needed to effectively mitigate organic aerosol pollution. 

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4. Particle formation and surface processes on atmospheric aerosols: A review of applied quantum chemical calculations

   https://doi.org/10.1002/qua.26350  

   Leonardi, Angelina; Ricker, Heather M.; Gale, Ariel G.; Ball, Benjamin T.; Odbadrakh, Tuguldur T.; Shields, George C.; Navea, Juan G. (June 2020, International Journal of Quantum Chemistry)

   Abstract Aerosols significantly influence atmospheric processes such as cloud nucleation, heterogeneous chemistry, and heavy‐metal transport in the troposphere. The chemical and physical complexity of atmospheric aerosols results in large uncertainties in their climate and health effects. In this article, we review recent advances in scientific understanding of aerosol processes achieved by the application of quantum chemical calculations. In particular, we emphasize recent work in two areas: new particle formation and heterogeneous processes. Details in quantum chemical methods are provided, elaborating on computational models for prenucleation, secondary organic aerosol formation, and aerosol interface phenomena. Modeling of relative humidity effects, aerosol surfaces, and chemical kinetics of reaction pathways is discussed. Because of their relevance, quantum chemical calculations and field and laboratory experiments are compared. In addition to describing the atmospheric relevance of the computational models, this article also presents future challenges in quantum chemical calculations applied to aerosols. 

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5. The Effects of Reactant Concentration and Air Flow Rate in the Consumption of Dissolved O2 during the Photochemistry of Aqueous Pyruvic Acid

   https://doi.org/10.3390/molecules24061124  

   Eugene, Alexis; Guzman, Marcelo (March 2019, Molecules)

   The sunlight photochemistry of the organic chromophore pyruvic acid (PA) in water generates ketyl and acetyl radicals that contribute to the production and processing of atmospheric aerosols. The photochemical mechanism is highly sensitive to dissolved oxygen content, [O2(aq)], among other environmental conditions. Thus, herein we investigate the photolysis (λ ≥ 305 nm) of 10–200 mM PA at pH 1.0 in water covering the relevant range 0 ≤ [O2(aq)] ≤ 1.3 mM. The rapid consumption of dissolved oxygen by the intermediate photolytic radicals is monitored in real time with a dissolved oxygen electrode. In addition, the rate of O2(aq) consumption is studied at air flow rates from 30.0 to 900.0 mL min−1. For the range of [PA]0 covered under air saturated conditions and 30 mL min−1 flow of air in this setup, the estimated half-lives of O2(aq) consumed by the photolytic radicalsfall within the interval from 22 to 3 min. Therefore, the corresponding depths of penetration of O2(g) into water (x = 4.3 and 1.6 µm) are determined, suggesting that accumulation and small coarse mode aqueous particles should not be O2-depleted in the presence of sunlight photons impinging this kind of chromophore. These photochemical results are of major tropospheric relevance for understanding the formation and growth of secondary organic aerosol. 

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