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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.

Recent experiments have revealed a vital nucleation process of iodic acid (HIO 3) and iodous acid (HIO 2) under marine boundary layer conditions. However, HIO 3 –HIO 2 nucleation may not effectively drive the observed rapid new particle formation (NPF) in certain coastal regions influenced by urban air masses. Dimethylamine (DMA) is a promising basic precursor to enhance nucleation considering its strong ability to stabilize acidic clusters and the wide distribution in marine atmosphere, while its role in HIO 3 –HIO 2 nucleation remains unrevealed. Hence, a method combining quantum chemical calculations and Atmospheric Cluster Dynamics Code (ACDC) simulations was utilized to study the HIO 3 –HIO 2 –DMA nucleation process. We found that DMA can preferentially accept the proton from HIO 3 as a basic precursor in the most stable configurations of HIO 3 –HIO 2 –DMA clusters. Kinetically, the participation of DMA in the cluster formation pathways of the iodine oxoacid system could be significant at the 10 -1 to 1 pptv level of [DMA]. Furthermore, DMA can enhance the cluster formation rates of the HIO 3 –HIO 2 system in marine and polar regions near DMA sources more than 10 3 -fold. Compared to the classical nucleation mechanism, the HIO 3 –HIO 2 –DMA mechanism exhibits strong nucleation ability, worthy of consideration as a promising mechanism in marine and polar regions rich in amine sources. The newly proposed HIO 3 –HIO 2 –DMA ternary mechanism might provide an explanation for some missing fluxes of atmospheric iodine particles. [ABSTRACT FROM AUTHOR]

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]

Iodic acid (HIO 3) and iodous acid (HIO 2) have been identified as nucleating effectively by the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at CERN, yet it may be hard to explain all HIO 3 -induced nucleation. Given the complexity of marine atmosphere, other precursors may be involved. Methanesulfonic acid (MSA), as a widespread precursor over oceans, has been proven to play a vital role in facilitating nucleation. However, its kinetic impacts on the synergistic nucleation of iodine oxoacids remain unclear. Hence, we investigated the MSA-involved HIO 3 –HIO 2 nucleation process at the molecular level using density functional theory (DFT) and the Atmospheric Cluster Dynamics Code (ACDC). Our results show that MSA can form stable molecular clusters with HIO 3 and HIO 2 jointed via hydrogen bonds, halogen bonds, and electrostatic attraction after proton transfer to HIO 2. Thermodynamically, the MSA-involved clustering can occur nearly without a free-energy barrier, following the HIO 2 –MSA binary and HIO 3 –HIO 2 –MSA ternary pathway. Furthermore, our results show that considering MSA will significantly enhance the calculated rate of HIO 3 –HIO 2 -based cluster formation, by up to 104 -fold in cold marine regions containing rich MSA and scarce iodine, such as the polar regions Ny-Ålesund and Marambio. Thus, the proposed more efficient HIO 3 –HIO 2 –MSA nucleation mechanism may provide theoretical evidence for explaining the frequent and intensive bursts of marine iodine particles. [ABSTRACT FROM AUTHOR]

Recent experiment (He et al, 2021, Science) revealed a vital nucleation process of iodic acid (HIO3) and iodous acid (HIO2) under the marine boundary layer conditions. However, HIO3-HIO2 nucleation cannot effectively derive the observed rapid new particle formation (NPF) in broad marine regions. Dimethylamine (DMA) is a promising basic precursor to enhance nucleation considering its strong ability to stabilize acidic clusters and the wide distribution in marine atmosphere, while its role in HIO3-HIO2 nucleation remains unrevealed. Hence, a method combining quantum chemical calculations and Atmospheric Cluster Dynamics Code (ACDC) simulations was utilized to study the HIO3-HIO2-DMA nucleation process. We found that DMA can compete with HIO2 to accept the proton from HIO3 as a basic precursor in the most stable configurations of HIO3-HIO2-DMA clusters. DMA can significantly enhance the cluster formation rates of HIO3-HIO2 kinetically for more than 103-fold in regions with abundant amine and scarce iodine based on combined factors of high nucleation ability and high concentration of DMA. Furthermore, the iodine oxoacids nucleation enhanced by DMA may explain the sources of rapid NPF events under different conditions corresponding to multiple ocean regions, which can provide important inspirations to understand the frequent and intensive NPF events in broad marine regions. [ABSTRACT FROM AUTHOR]

Iodic acid (HIO3) and iodous acid (HIO2) have been identified to nucleate effectively by the Cosmics Leaving OUtdoor Droplets (CLOUD) experiment at CERN (He et al., 2021, Science), yet it may be hard to explain all HIO3-induced nucleation. Given the complexity of marine atmosphere, other precursors may be involved. Methanesulfonic acid (MSA), as a widespread precursor over oceans, has been proven to play a vital role in facilitating nucleation. However, its kinetic impacts on synergistic nucleation of iodine oxoacids remain unclear. Hence, we investigated the MSA-involved HIO3-HIO2 nucleation process at the molecular level using density functional theory (DFT) and Atmospheric Clusters Dynamic Code (ACDC). The results show that MSA can form stable molecular clusters with HIO3 and HIO2 jointly via hydrogen and halogen bonds, as well as electrostatic attraction after proton transfer to HIO2. Thermodynamically, the MSA-involved clustering can occur nearly without free-energy barrier, following HIO2-MSA binary and HIO3-HIO2-MSA ternary pathway. Furthermore, adding MSA significantly enhance the rate of HIO3-HIO2-based cluster formation, even up to 104-fold at cold marine regions with rich MSA and scarce iodine, such as polar Ny-Ålesund and Marambio. Thus, the proposed more efficient HIO3-HIO2-MSA nucleation mechanism may provide theoretical evidence for explaining the frequent and intensive burst of marine iodine particles. [ABSTRACT FROM AUTHOR]

Diiodine trioxide (I2O3) is one of the most common iodine oxides in the marine boundary layer (MBL). Both theoretical and experimental studies have confirmed that they can be quickly formed and are relatively stable under dry conditions. However, there is no report on the field observation of I2O3, which means that I2O3 is likely to be lost in the actual marine atmosphere. But the specific loss pathways and mechanisms are still unclear. Considering that the humidity in the marine regions is generally high and the loss of I2O3 will be affected by some substances in the marine atmosphere, water (H2O, W) and iodic acid (HIO3, IA) were selected as a catalyst to investigate the catalytic hydration mechanisms of I2O3 at DLPNOCCSD(T)//ωB97X-D/aug-cc-pVTZ + aug-cc-pVTZ -PP (for iodine) level of theory. The results show that hydration of I2O3 presents a high energy barrier, but IA can reduce it to 3.76 kcal/mol. Therefore, in the marine atmosphere, I2O3 can be hydrolyzed under the catalysis of IA, and cannot directly participate in the new particle formation process.

By seeding clouds, new particle formation (NPF) has a substantial impact on radiation balance, bio-geochemical cycles and global climate. Over oceans, both methanesulfonic acid (CH3S(O)2OH, MSA) and iodous acid (HIO2) have been reported to be closely associated with NPF events; however, much less is known about whether they can jointly nucleate to form nanoclusters. Hence, quantum chemical calculations and Atmospheric Cluster Dynamics Code (ACDC) simulations were performed to investigate the novel mechanism of MSA–HIO2 binary nucleation. The results indicate that MSA and HIO2 can form stable clusters via multiple interactions including hydrogen bonds, halogen bonds, and electrostatic forces between ion pairs after proton transfer, which are more diverse than those in MSA–iodic acid (HIO3) and MSA–dimethylamine (DMA) clusters. Interestingly, HIO2 can be protonated by MSA exhibiting base-like behavior, but it differs from base nucleation precursors by self-nucleation rather than solely binding to MSA. Due to the greater stability of MSA–HIO2 clusters, the formation rate of MSA–HIO2 clusters can be even higher than that of MSA–DMA clusters, suggesting that MSA–HIO2 nucleation is a non-negligible source of marine NPF. This work proposes a novel mechanism of MSA–HIO2 binary nucleation for marine aerosols and provides deeper insights into the distinctive nucleation characteristics of HIO2, which can help in constructing a more comprehensive sulfur- and iodine-bearing nucleation model for marine NPF. [ABSTRACT FROM AUTHOR]

Multi-stage launch vehicles are currently the primary tool for humans to reach extraterrestrial space. The technology of recovering and reusing rockets can effectively shorten rocket launch cycles and reduce space launch costs. With the development of deep representation learning, reinforcement learning (RL) has become a robust learning framework capable of learning complex policies in high-dimensional environments. In this paper, a deep reinforcement learning-based reusable rocket landing control method is proposed. The mathematical process of reusable rocket landing is modelled by considering the aerodynamic drag, thrust, gravitational force, and Earth's rotation during the landing process. A reward function is designed according to the rewards and penalties derived from mission accomplishment, terminal constraints, and landing performance. Based on this, the Softmax double deep deterministic policy gradient (SD3) deep RL method is applied to build a robust reusable rocket landing control method. In the constructed simulation environment, the proposed method can achieve convergent and robust control results, proving the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]