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Recent research [Wang et al., Nature 581, 184-189 (2020)] indicates nitric acid (NA) can participate in sulfuric acid (SA)-ammonia (NH3) nucleation in the clean and cold upper free troposphere, whereas NA exhibits no obvious effects at the boundary layer with relatively high temperatures. Herein, considering that an SA-dimethylamine (DMA) nucleation mechanism was detected in megacities [Yao et al., Science 361, 278-281 (2018)], the roles of NA in SA-DMA nucleation are investigated. Different from SA-NH3 nucleation, we found that NA can enhance SA-DMA-based particle formation rates in the polluted atmospheric boundary layer, such as Beijing in winter, with the enhancement up to 80-fold. Moreover, we found that NA can promote the number concentrations of nucleation clusters (up to 27-fold) and contribute 76% of cluster formation pathways at 280 K. The enhancements on particle formation by NA are critical for particulate pollution in the polluted boundary layer with relatively high NA and DMA concentrations. [ABSTRACT FROM AUTHOR]

Wet processes, including aqueous phase chemistry, wet scavenging, and wet surface uptakes during dry deposition, are important for global modeling of aerosol precursors and aerosols. In this study, we improved the treatments of these wet processes in the GEOS-Chem v12.6.0, including pH calculation for cloud, rain, and wet surface, fraction of cloud available for aqueous phase chemistry, rainout efficiencies for various types of cloud, empirical washout by rain and snow, and wet surface uptakes during dry deposition. We compared simulated surface mass concentrations of aerosol precursors and aerosols with surface monitoring networks over the United States, Europe, Asia, and Arctic regions, and showed that the model results with the updated wet processes agree better with measurements for most species. With the implementation of these updates, normalized mean biases (NMB) of surface nitric acid, nitrate, and ammonium are reduced from 78 %, 126 %, and 45 % to 13 %, 24 %, and 6.2 % over US sites, from 56 %, 105 %, and 91 % to -20 %, -5.1 %, and 22 % over Europe sites, and from 121 %, 269 %, and 167 % to -18 %, 40 %, and 86 % over Asia sites. Comparison with surface measured SO2, sulfate and black carbon at four Arctic sites indicated that these species simulated with the updated wet processes match well with observations except large underestimation of black carbon at one of the sites. Furthermore, we compared model simulation with aircraft measurement of nitric acid and aerosols during ATom-1 and ATom-2 periods and found seasonal variation and vertical profile of these species have been successfully improved by considering the updated wet processes. The investigation of impacts of updated wet process treatments on surface mass concentrations indicated that the updated wet processes have strong impacts on the global means of nitric acid, sulfate, nitrate, and ammonium and relative small impacts on the global means of sulfur dioxide, dust, sea salt, black carbon, and organic carbon. [ABSTRACT FROM AUTHOR]

Formation of new particles in the atmosphere have important implications for air quality and climate. Recently, we have developed a kinetically-based H2SO4-H2O-NH3-Ions nucleation model which captures well the absolute values of nucleation rates as well as dependencies of nucleation rates on NH3 and H2SO4 concentrations, ionization rates, temperature, and relative humidity observed in the well-controlled Cosmics Leaving OUtdoor Droplets (CLOUD) measurements. Here we employ the aforementioned recently developed kinetic nucleation model to generate nucleation rate look-up tables for H2SO4-H2O binary homogenous nucleation (BHN), H2SO4-H2O-NH3 ternary homogeneous nucleation (THN), H2SO4-H2O-Ions binary ion-mediated nucleation (BIMN), and H2SO4-H2O-NH3-Ions ternary ion-mediated nucleation (TIMN). A comparison of nucleation rates calculated using the lookup tables with CLOUD measurements of BHN, BIMN, THN, and TIMN is presented. The lookup tables cover a wide range of key parameters controlling binary, ternary and ion-mediated nucleation in the Earth's atmosphere, and are a cost-efficient solution for multi-dimensional modeling. The lookup tables and FORTRAN codes, made available through this work, can be readily used for BHN, THN, BIMN, and TIMN simulations in 3-D modeling. The lookup tables can also be used by experimentalists involved in laboratory and field measurements for a quick assessment of nucleation involving H2SO4, H2O, NH3, and Ions. [ABSTRACT FROM AUTHOR]

The classical Kelvin–Thomson (CKT) equation does not consider the interaction of condensing molecules with the ions and hence is not able to treat polar and nonpolar molecules differently. The ion-clustering enthalpy and entropy changes predicted by CKT equation for small ions are known to be significantly less negative than those observed. In this paper, we derive a modified Kelvin–Thomson (MKT) equation, which considers the effect of dipole-ion interaction, by taking into account the kinetic energy change of condensing polar ligands as they approach the ions or the extra energy needed for dipole molecules to escape from the ion cluster. The clustering enthalpies and entropies for protonated clusters (H+Ln, with L=H2O, NH3, CH3OH, and C5H5N) are calculated based on MKT equation and compared with experimental data. Our calculations indicate that enthalpy values given by MKT equation are in very good agreement with experimental results for small ions (n≤5) of all four species investigated. MKT predictions appear to be consistent with observed enthalpies for CH3OH at n>=6 and for H2O at n=14–25, however, MKT equation cannot reproduce the observed discontinuous transition in enthalpy changes at n=6 for NH3 and at n=7–13 for H2O which is probably associated with the formation of inner shell. The stepwise entropy changes for small ions are 5–15 cal mol-1 K-1 more negative when the effect of dipole-ion interaction is considered, which suggests that the ordered structure of the cluster ions can somewhat be accounted for by the dipole-ion interaction term. [ABSTRACT FROM AUTHOR]

The widely used community model GEOS-Chem 12.0.0 and previous versions have been recognized to significantly overestimate the concentrations of gaseous nitric acid, aerosol nitrate, and aerosol ammonium over the United States. The concentrations of nitric acid are also significantly over-predicted in most global models participating a recent model inter-comparison study. In this study, we show that most or all of this overestimation issue appears to be associated with wet scavenging processes. Replacement of constant in-cloud condensation water (ICCW) assumed in GEOS-Chem standard versions with one varying with location and time from the assimilated meteorology significantly reduces mass loadings of nitrate and ammonium during the wintertime, while the employment of an empirical washout rate for nitric acid significantly decreases mass concentrations of nitric acid and ammonium during the summertime. Compared to the standard version, GEOS-Chem with updated ICCW and washout rate significantly reduces the simulated annual mean mass concentrations of nitric acid, nitrate, and ammonium at surface mentoring network sites in US, from 2.04 to 1.03μgm-3, 1.89 to 0.88μgm-3, 1.09 to 0.68μgm-3, respectively, in much better agreement with corresponding observed values of 0.83, 0.70, and 0.60 μg m-3, respectively. In addition, the agreement of model simulated seasonal variations of corresponding species with measurements is also improved. The updated wet scavenging scheme improves the skill of the model in predicting nitric acid, nitrate, and ammonium concentrations which are important species for air quality and climate. [ABSTRACT FROM AUTHOR]

The impact of organic species which are present in the Earth's atmosphere on the burst of new particles is critically important for the understanding of the molecular nature of atmospheric nucleation phenomena. Amines have recently been proposed as possible stabilizers of binary pre-nucleation clusters. In order to advance the understanding of atmospheric nucleation phenomena, a quantum-chemical study of hydrogen-bonded complexes of binary sulfuric acid-water clusters with methyl-, dimethyl- and trimethylamines representing common atmospheric organic species, vegetation products and laboratory impurities has been carried out. The thermochemical stability of the sulfuric acid-amines-water complexes was found to be higher than that of the sulfuric acid-ammonia-water complexes, in qualitative agreement with the previous studies. However, the enhancement in stability due to amines appears to not be large enough to overcome the difference in typical atmospheric concentrations of ammonia and amines. Further research is needed in order to address the existing uncertainties and to reach a final conclusion about the importance of amines for the atmospheric nucleation. [ABSTRACT FROM AUTHOR]

The cloud condensation nuclei concentrations predicted by global aerosol models are sensitive to how new particle formation in subgrid anthropogenic SO2 plumes is parameterized. Using a state-of-the-art kinetic nucleation model, we carried out two case studies to investigate the large difference in the number concentrations of ultrafine particles observed in the plumes from the Horne smelter: one in the summer and the other in the winter. Our model predicted that particle number concentrations are in good agreement with observations for both cases, showing that particle formation in the Horne smelter plumes is dominated by binary homogeneous nucleation (BHN) in the winter case and by ion-mediated nucleation (IMN) in the summer case. Further sensitivity studies reveal significant diurnal and seasonal variations of sulfate particle formation in the anthropogenic SO2 plume, mainly associated with corresponding variations of two key parameters: hydroxyl radical concentration ([OH]) and temperature. Nucleation in the plume is negligible at night because of very low [OH]. BHN is significant when [OH] is relatively high or temperature is relatively low, and it is generally limited to the fresh plumes (within 15 km from source), but it can generate very high concentrations of ultrafine particles (peak values as high as 105-106 cm-3) under favorable conditions. IMN generally dominates nucleation in the plume when [OH] is relatively low or temperature is relatively high, and it extends from fresh plume to more aged plume and produces 2-3 × 104 cm-3 of nucleated particles. The implications of the results are discussed. [ABSTRACT FROM AUTHOR]

The sign preference of hydrogen bonded aqueous ionic clusters ?±(H2O)i (n =1-5, ? = F; Cl; Br) has been investigated using the Density Functional Theory and ab initio MP2 method. The present study indicates the anomalously large difference in formation free energies between cations and anions of identical chemical composition. The effect of vibrational anharmonicity on stepwise Gibbs free energy changes has been investigated, and possible uncertainties associated with the harmonic treatment of vibrational spectra have been discussed. [ABSTRACT FROM AUTHOR]

Sulfuric acid is a primary atmospheric nucleation precursor, with the ability to form stable aqueous hydrogen-bonded clusters/complexes. The electrical dipole moment of such clusters/complexes is important for ion-induced nucleation, largely controlled by dipole−charge interaction of airborne ions with vapor monomers and pre-existing clusters. Although experiments typically trace a single lowest energy conformer at low temperatures, the present study shows that the immediate vicinity (<1 kcal mol −1) of the global minima may be populated with a number of isomers of nearly identical spectral characteristics and drastically different dipole moments. The difference in the dipole moment of mono-, di-, and trihydrates of the sulfuric acid exceeds 1.3−1.5 Debyes (∼50−60%), 1.4−2.6 Debyes (∼50−90%), and 3.8−4.2 Debyes (∼370−550%), respectively. Being driven by the temperature dependence of the Boltzmann distribution, the difference between the Boltzmann−Gibbs average dipole moment and the dipole moment of the most stable isomer increases with the ambient temperature, leading to large variations in the dipole−ion interaction strength, which may have important implications for the ion-mediated production of ultrafine aerosol particles associated with various climatic and health impacts. [ABSTRACT FROM AUTHOR]

We propose a source of aerosols in the lower atmosphere associated with the creation, growth, and recombination of ubiquitous cosmogenically generated ions. This particle source should be favorable in the relatively clean, stable marine boundary layer, providing a uniform, continuous fine particle generator in the presence of dimethylsulfide emissions. Through this mechanism, new sulfate aerosols can be formed at sulfuric acid vapor partial pressures well below the supersaturations required for homogeneous binary nucleation of sulfuric acid/water solutions, which is consistent with numerous observations of new particle formation under sub-saturated conditions. The evolving aerosols in turn control the acid vapor concentration and thus modulate the sizes of the precursor ions and the rate of new particle formation. A simple model representing this nonlinear coupled system predicts that the physical and chemical processes connecting ions, vapors, and aerosols effectively constrain the particle population to a relatively narrow range of values. This self-limiting behavior may explain in part the apparent stability of the marine sulfate aerosol, with mean concentrations of the order of several hundred per cubic centimeter. [ABSTRACT FROM AUTHOR]

Aerosol-cloud interactions (ACIs) are vital for regulating Earth's climate by influencing energy and water cycles. Yet, effects of ACI bear large uncertainties, evidenced by systematic discrepancies between observed and modeled estimates. This study quantifies a major bias in ACI determinations, stemming from conventional surface or space measurements that fail to capture aerosol at the cloud level unless the cloud is coupled with land surface. We introduce an advanced approach to determine radiative forcing of ACI by accounting for cloud-surface coupling. By integrating field observations, satellite data, and model simulations, this approach reveals a drastic alteration in aerosol vertical transport and ACI effects caused by cloud coupling. In coupled regimes, aerosols enhance cloud droplet number concentration across the boundary layer more homogeneously than in decoupled conditions, under which aerosols from the free atmosphere predominantly affect cloud properties, leading to marked cooling effects. Our findings spotlight cloud-surface coupling as a key factor for ACI quantification, hinting at potential underassessments in traditional estimates. [ABSTRACT FROM AUTHOR]

Ice crystal habit significantly impacts ice crystal processes such as growth by vapor deposition. Despite this, most bulk microphysical models disregard this natural shape effect and assume ice to grow spherically. This paper focuses on how the evolution of ice crystal shape and choice of ice nucleation parameterization in the adaptive habit microphysics model (AHM) influence the lake-effect storm that occurred during intensive observing period 4 (IOP4) of the Ontario Winter Lake-effect Systems (OWLeS) field campaign. This localized snowstorm produced total accumulated liquid-equivalent precipitation amounts up to 17.92mm during a 16-h time period, providing a natural laboratory to investigate the ice--liquid partitioning within the cloud, various microphysical process rates, the accumulated precipitation magnitude, and its associated spatial distribution. Two nucleation parameterizations were implemented, and aerosol data from a size-resolved advanced particle microphysics (APM) model were ingested into the AHM for use in parameterizing ice and cloud condensation nuclei. Simulations allowing ice crystals to grow nonspherically produced 1.6%-2.3% greater precipitation while altering the nucleation parameterization changed the type of accumulating hydrometeors. In addition, all simulations were highly sensitive to the domain resolution and the source of initial and boundary conditions. These findings form the foundational understanding of relationships among ice crystal habit, nucleation parameterizations, and resultant cold-season mesoscale precipitation within detailed bulk microphysical models allowing adaptive habit. [ABSTRACT FROM AUTHOR]

Amines, organic derivatives of NH3, are important common trace atmospheric species that can enhance new particle formation in the Earth's atmosphere under favorable conditions. While methylamine (MA), dimethylamine (DMA) and trimethylamine (TMA) all efficiently enhance binary nucleation, MA may represent the lower limit of the enhancing effect of amines on atmospheric nucleation. In the present paper, we report new thermochemical data concerning MA-enhanced nucleation, which were obtained using the DFT PW91PW91/6-311++G (3df, 3pd) method, and investigate the enhancement in production of stable pre-nucleation clusters due to the MA. We found that the MA ternary nucleation begins to dominate over ternary nucleation of sulfuric acid, water and ammonia at [MA]/[NH3] > ~10-3. This means that under real atmospheric conditions ([MA] ~ 1 ppt, [NH3] ~ 1 ppb) the lower limit of the enhancement due to methylamines is either close to or higher than the typical effect of NH3. A very strong impact of the MA is observed at low RH; however it decreases quickly as the RH grows. Low RH and low ambient temperatures were found to be particularly favorable for the enhancement in production of stable sulfuric acid-water clusters due to the MA. [ABSTRACT FROM AUTHOR]

In the present Letter, the enhancing effect of dimethylamine (DMA) on the production of stable H2SO4-H2O clusters have been studied using the Density Functional Theory (DFT). It has been pointed out that the DMA concentrations of 1-10 ppt are needed in order to achieve a considerable enhancement in production of sulfuric acid-water clusters under typical atmospheric conditions and that the ambient RH plays a significant role at the early stages of the gas-to cluster conversion in the ternary DMA-H2SO4-H2O vapour mixtures. Large uncertainties in the thermochemistry of amine-enhanced nucleation have been pointed out and discussed. [ABSTRACT FROM AUTHOR]