Search

Clustering of gaseous sulfuric acid (SA) enhanced by dimethylamine (DMA) is a major mechanism for new particle formation (NPF) in polluted atmospheres. However, uncertainty remains regarding the SA-DMA nucleation parameterization that reasonably represents cluster dynamics and is applicable across various atmospheric conditions. This uncertainty hinders accurate three-dimensional (3-D) modeling of NPF and subsequent assessment of its environmental and climatic impacts. Here we extensively compare different cluster dynamics-based parameterizations for SA-DMA nucleation and identify the most reliable one through a combination of box-model simulations, 3-D modeling, and in-situ observations. Results show that the parameterization derived from Atmospheric Cluster Dynamic Code (ACDC) simulations, incorporating the latest theoretical insights (DLPNO-CCSD(T)/aug-cc-pVTZ//ωB97X-D/6-311++G(3df,3pd) level of theory) and adequate representation of cluster dynamics, exhibits dependable performance in 3-D NPF simulation for both winter and summer conditions in Beijing and shows promise for application in diverse atmospheric conditions. Another ACDC-derived parameterization, replacing the level of theory with RI-CC2/aug-cc-pV(T+d)Z//M06-2X/6–311++G(3df,3pd), also performs well in NPF modeling at relatively low temperatures around 280 K but exhibits limitations at higher temperatures due to inappropriate representation of SA-DMA cluster thermodynamics. Additionally, a previously reported parameterization incorporating simplifications is applicable for simulating NPF in polluted atmospheres but tends to overestimate particle formation rates under conditions of elevated temperature (> ~300 K) and low condensation sink (< ~3×10-3 s-1). Our findings highlight the applicability of the new ACDC-derived parameterization, which couples the latest SA-DMA nucleation theory and holistic cluster dynamics, in 3-D NPF modeling. The ACDC-derived parameterization framework provides valuable reference for developing parameterizations for other nucleation systems. [ABSTRACT FROM AUTHOR]

Marine new particle formation (NPF) can affect cloud condensation nuclei (CCN) in the global atmosphere. Recently, iodic acid (IA) has been identified as a critical driver for marine NPF. However, atmospheric observations of IA cannot be associated with predicted particle formation rates. Given the complexity of atmospheric components, other species may promote IA particle formation. As an efficient stabilizer for acidic precursors, dimethylamine (DMA) has a wide distribution over the oceans. Hence, we investigated the nucleation process of DMA and IA under different atmospheric conditions and uncovered the corresponding nucleating mechanism using a quantum chemical approach and Atmospheric Cluster Dynamics Code (ACDC). The findings show that DMA can structurally stabilize IA via hydrogen and halogen bonds, and the clustering process is energy barrierless. Moreover, DMA can enhance the formation rate of IA clusters by five orders of magnitude, and its efficiency in promoting IA cluster formation is much higher than that of NH3. Compared to the nucleation via sequential addition of IA, the IA-DMA nucleation plays a more dominant role in nucleation kinetic. Thus, the effect of DMA on enhancing IA cluster stability and formation rate cannot be ignored, especially in the regions near the source of IA and DMA emissions. Broadly, the proposed IA-DMA nucleation mechanism may help to explain some missing sources of particles and, thus intensive marine NPF events. [ABSTRACT FROM AUTHOR]

Transformation of low-volatility gaseous precursors to new particles affects aerosol number concentration, cloud formation and hence the climate. The clustering of acid and base molecules is a major mechanism driving fast nucleation and initial growth of new particles in the atmosphere. However, the acid–base cluster composition, measured using state-of-the-art mass spectrometers, cannot explain the measured high formation rate of new particles. Here we present strong evidence for the existence of base molecules such as amines in the smallest atmospheric sulfuric acid clusters prior to their detection by mass spectrometers. We demonstrate that forming (H2SO4)1(amine)1 is the rate-limiting step in atmospheric H2SO4-amine nucleation and the uptake of (H2SO4)1(amine)1 is a major pathway for the initial growth of H2SO4 clusters. The proposed mechanism is very consistent with measured new particle formation in urban Beijing, in which dimethylamine is the key base for H2SO4 nucleation while other bases such as ammonia may contribute to the growth of larger clusters. Our findings further underline the fact that strong amines, even at low concentrations and when undetected in the smallest clusters, can be crucial to particle formation in the planetary boundary layer. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Sulfuric acid (SA)‐dimethylamine (DMA)‐H2O cluster formation has been proven to be responsible for a significant part of new particle formation (NPF) in a Chinese megacity. However, the possible involvement of common atmospheric acids in the subsequent growth of SA‐DMA clusters remains elusive. We simulated formation and growth of clusters using atmospheric relevant concentrations of SA, DMA, and trifluoroacetic acid (TFA), a commonly observed atmospheric perfluorocarboxylic acid, using Density Functional Theory combined with Atmospheric Cluster Dynamics Code. The presence of TFA leads to complex cluster formation routes and an enhancement of NPF rates by up to 2.3 ([TFA] = 5.0 × 106 molecules cm−3, [SA] = 1.0 × 106 molecules cm−3, and [DMA] = 1.5 × 109 molecules cm−3). The agreement of (SA)1·(DMA)1‐2·(TFA)1 concentrations between simulations and ambient measurements during NPF events validates model predictions and implies that perfluorocarboxylic acids could potentially boost atmospheric SA‐DMA NPF rates. Plain Language Summary: Atmospheric nucleation is the earliest step to form new aerosol particles, which includes a complex transformation from gaseous molecules to small clusters, then to critical clusters, and finally to freshly nucleated nanoparticles. Sulfuric acid and dimethylamine have been proved to explain atmospheric nucleation events in urban China. However, whether other atmospheric acidic species could participate in this nucleation process remains elusive. Herein, we report a sulfuric acid‐dimethylamine based nucleation mechanism with the participation of trifluoroacetic acid, a commonly observed strong acid in the atmosphere, using theoretical calculation methods. The model predictions are then validated by ambient measurements in urban Shanghai. Our results suggest that perfluorocarboxylic acids could potentially boost the formation of nanoparticles. Key Points: Theoretical simulations indicate complex atmospheric new particle formation mechanisms involving sulfuric acid, dimethylamine, and trifluoroacetic acidGood agreement of key cluster concentrations between simulations and ambient measurements during new particle formation events is obtainedTrifluoroacetic acid can participate in the growth of sulfuric acid‐dimethylamine clusters and enhance the nucleation rates [ABSTRACT FROM AUTHOR]

It is well established that oxidation products of volatile organic compounds (VOCs) play a major role in atmospheric new-particle formation (NPF). However, the mechanism of their effect and the corresponding influence under various atmospheric conditions remain unclear. Meanwhile, considering the difficulty of experiment in determining the water content of the cluster and performing at low temperature, we combine Density Functional Theory (DFT) and Atmospheric Clusters Dynamic Code (ACDC) model to investigate a multicomponent system involving lactic acid ( LA ) and atmospheric nucleation precursors (sulfuric acid ( SA ), dimethylamine ( DMA ), water ( W )) under a wide range of atmospheric conditions (relative humidity ( RH ) from 20% to 100%, temperature ( T ) from 220 K to 300 K). Conformational analysis shows that LA could enhance NPF in two direction due to its two highly oxidized function groups. Then, the results from ACDC simulation present a direct evidence of its enhancement effect on NPF when the concentration of LA is larger than 10 10 molecules cm − 3 . The corresponding enhancement strength presents a positive dependence on its concentrations and a negative dependence on RH and T , respectively. Besides, LA ·n W (n = 0–1) reflect their enhancement effect on the cluster growth paths by acting as “bridge”, which contributes to pure SA - DMA - W -based clusters by evaporating LA contained clusters. The corresponding contribution presents a positive dependence on the concentration of LA , RH and T , respectively. We hope our study could provide theoretical clues to better understand the characteristic of NPF in polluted area, where NPF commonly involves oxidized organics, sulfuric acid, amine and water. [ABSTRACT FROM AUTHOR]

A recent quantitative measurement of rates of new particle formation (NPF) in urban Shanghai showed that the high rates of NPF can be largely attributed to the sulfuric acid (SA)-dimethylamine (DMA) nucleation due to relatively high DMA concentration in urban atmosphere (Yao et al., Science. 2018 , 361 , 278). In certain atmospheric conditions, the release of DMA is accompanied with the emission of high concentration of ammonia. As a result, the ammonia (A) may participate in SA-DMA-based NPF. However, the main sources of DMA and A can be different, thereby leading to different mechanism for the SA-DMA-A-based nucleation under different atmospheric conditions. Near industrial sources with relatively high DMA concentration of 108 molecules cm−3, the contribution of binary SA-DMA nucleation to cluster formation is 61% at 278 K, representing a dominant pathway for NPF. However, in the region not too close to major source of DMA emission, e.g., near agriculture farmland, the routes involving ternary SA-DMA-A nucleation make a 64% contribution at 278 K with DMA concentration of 107 molecules cm−3, showing that A has marked impact on the cluster formation. Under such a condition, we predict that coexisting DMA and A could be detected in the process of NPF. Moreover, at winter temperatures or at higher altitudes, our calculations suggest that the clustering of initial clusters likely involve ternary SA-DMA-A clusters rather than binary SA-DMA clusters. These new insights may be helpful to analyze and predict atmospheric-condition-dependent NFP in either urban or rural regions and/or in different season of the year. Image 1 • Near industrial sources with high [DMA], the binary SA-DMA nucleation is predominant. • Near agriculture farmland, high [A] can have marked impact on the cluster formation. • At relatively low temperature, the particle formation more likely involves molecule A. • This paper can provide a better understanding of atmospheric-condition-dependent NPF. [ABSTRACT FROM AUTHOR]