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(1) Introduction. Although new particle formation (NPF) constitutes an important process in air, there are large uncertainties regarding which species participate in the formation of the first nanoclusters. Acid-base reactions are known generate new particles, with methanesulfonic acid (MSA) from the photooxidation of biogenic organosulfur compounds becoming more important with time relative to sulfuric acid as fossil-fuel related sources of the latter decline. Simultaneously, the use of alkanolamines in carbon capture and storage (CCS) is expected to result in increased atmospheric concentrations of these bases. This study applied a unique mass spectrometry method to examine the chemical composition of 2-10 nm particles from the MSA reaction with monoethanolamine and 4-aminobutanol, the most efficient system for NPF from MSA examined to date. (2) Methods. Thermal desorption chemical ionization mass spectrometry (TDCIMS, HToF mass analyzer, Tofwerk AG) was used to measure the size and acid-to-base molar ratios of nanoparticles formed from the reaction of MSA with multifunctional amines. A high-flow differential mobility analyzer (half-mini DMA, SEADM) was interfaced with the TDCIMS, which provides a high mobility resolution and high particle transmission in the diameter range 2-10 nm, where chemical composition measurements are the most challenging due to the very small amount of mass. With this novel combination of techniques we were able to examine MSA-amine systems either from nanoparticles exiting the outlet of a flow reactor or nanoclusters generated via electrospray. (3) Preliminary Data. These experiments show that MSA-driven acid-base reactions with monethanolamine or 4-aminobutanol are even more efficient in NPF than that of simple alkylamines, exhibiting to date the highest nanoparticle formation rates measured in laboratory flow tube studies. The observed enhancement is rooted in the presence of an -OH group on the parent molecules, which initiates a H-bond network throughout the nanoclusters. In these systems, water had only a minimal enhancing effect. We demonstrated that the nanoparticles formed in both systems are neutral (i.e. contain as much acid as base molecules) in the range 2-10 nm. This contrasts with MSA reactions from previous studies on the smallest alkylamine, methylamine, where particles smaller than 9 nm were more acidic. Investigations of reactions of MSA with a diamine (1,4-diaminobutane) showed a similar pattern of neutral particles across the diameter range studied and experiments with larger alkylamine, butylamine, are underway to probe the relationship between structure- and NPF potential from MSA. These findings highlight that there is no “one size-fits-all” regarding NPF from MSA reactions with amines and illustrates the need for studies of more complex amines to fully characterize the NPF potential of this atmospherically relevant strong acid. (4) Novel Aspect. The combination of TDCIMS with a novel particle sizing system provided the chemical composition of 2-10 nm particles. 

This study reports on the high yield of new particle formation (NPF) from the reaction of an alkanolamine commonly used in carbon capture and storage technology, monoethanolamine, with strong atmospherically relevant acid, methanesulfonic acid. 

The energy landscape is changing worldwide, with a drastic reduction in sulfur dioxide (precursor to sulfuric acid, H2SO4) emitted from fossil fuel combustion. As a result, acid-base chemistry leading to new particle formation (NPF) from sulfuric acid is decreasing. At the same time, photooxidation of biogenic organosulfur compounds leading to the formation of H2SO4 and methanesulfonic acid (MSA) is expected to become more important. Aqueous solutions of alkanolamines have been proposed as carbon capture technology media to store carbon dioxide from stack plumes before release into the atmosphere. It is therefore expected that some of the alkanolamines will be released, making it critical to understand their atmospheric fates including their role in new particle formation and growth. We expanded our experimental studies of nucleation from the reaction of MSA with simple amines to the multifunctional alkanolamines, including mononethanolamine (HO(CH2)2NH2; MEA) and 4-aminobutanol (HO(CH2)4NH2; 4AB). Experiments were performed in a 1-m borosilicate flow reactor under dry conditions as well as in presence of water. These two systems were shown to produce sub-10 nm particles with MSA extremely efficiently. Surprisingly, the presence of water did not enhance NPF, in contrast to the drastic effect water had on small alkylamine reactions with MSA. This is likely due to the fact that MEA and 4AB have an -OH group that provides additional H-bond interactions within the cluster. Sampling of the chemical composition of these small nanoparticles with high resolution and high transmission was possible down to 3-4 nm using a novel high-flow differential mobility analyzer (half-mini DMA) interfaced to a thermal chemical ionization mass spectrometer (TDCIMS). There was no size dependence for the acid-to-base molar ratio (1:1) for either amine. Integration of these data with preliminary results obtained for a simple C4 alkylamine (butylamine) and a C4 diamine (putrescine) will be discussed in the context of developing a molecular structure-reactivity scheme for new particle formation from MSA and amines of varying structures. 

Abstract As one of the least understood aerosol processes, nucleation can be a dominant source of atmospheric aerosols. Sulfuric acid (SA)-amine binary nucleation with dimethylamine (DMA) has been recognized as a governing mechanism in the polluted continental boundary layer. Here we demonstrate the importance of trimethylamine (TMA) for nucleation in the complex atmosphere and propose a molecular-level SA-DMA-TMA ternary nucleation mechanism as an improvement upon the conventional binary mechanism. Using the proposed mechanism, we could connect the gaseous amines to the SA-amine cluster signals measured in the atmosphere of urban Beijing. Results show that TMA can accelerate the SA-DMA-based new particle formation in Beijing by 50–100%. Considering the global abundance of TMA and DMA, our findings imply comparable importance of TMA and DMA to nucleation in the polluted continental boundary layer, with probably higher contributions from TMA in polluted rural environments and future urban environments with controlled DMA emissions. 

Abstract. Chemical ionization mass spectrometry with the nitrate reagent ion (NO3- CIMS) was used to investigate the products of the nitrate radical(NO3) initiated oxidation of four monoterpenes in laboratory chamber experiments. α-Pinene, β-pinene, Δ-3-carene, andα-thujene were studied. The major gas-phase species produced in each system were distinctly different, showing the effect of monoterpenestructure on the oxidation mechanism and further elucidating the contributions of these species to particle formation and growth. By comparinggroupings of products based on the ratios of elements in the general formula CwHxNyOz, therelative importance of specific mechanistic pathways (fragmentation, termination, and radical rearrangement) can be assessed for eachsystem. Additionally, the measured time series of the highly oxidized reaction products provide insights into the ratio of relative production andloss rates of the high-molecular-weight products of the Δ-3-carene system. The measured effective O:C ratios of reaction products wereanticorrelated with new particle formation intensity and number concentration for each system; however, the monomer : dimer ratios of products had a smallpositive trend. Gas-phase yields of oxidation products measured by NO3- CIMS correlated with particle number concentrations for eachmonoterpene system, with the exception of α-thujene, which produced a considerable amount of low-volatility products but noparticles. Species-resolved wall loss was measured with NO3- CIMS and found to be highly variable among oxidized reaction products in ourstainless steel chamber. 

This dataset includes aerosol microphysics and chemical measurements collected at Mt. Soledad and Scripps Pier during the Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) from February 2023 to February 2024. The measurements include the following instruments at Mt. Soledad: High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS, Aerodyne), Scanning Electrical Mobility Spectrometer (SEMS, Brechtel Manufacturing Inc.), Aerodynamic Particle Sizer (APS, Droplet Measurements Technologies), Single Particle Soot Photometer (SP2, Drople Measurements Technologies), Meteorological Station (WXT520, Vaisala), Ozone (Teco), and trace gas proxies (Teledyne). In addition, the analyses of particle filters collected at Mt. Soledad for three dry-diameter size cuts (<1 micron, <0.5 micron, <0.18 micron) and at Scripps Pier for one dry-diametr size cut (<1 micron) by Fourier Transform Infrared (FTIR) and X-ray Fluorescence (XRF) are reported. A differential mobility analyzer operated as a scanning mobility particle sizer (SMPS, TSI Inc.), a printed particle optical spectrometer (POPS, Grimm), and a continuous flow diffusion cloud condensation nuclei (CCN, DMT) counter provide the mobility aerosol size distribution (30-360 nm), optical size distribution (150 - 6000 nm), size-resolved CCN distribution (30-360 nm) at 0.2, 0.4, 0.6, 0.8, and 1.0% supersaturation. Measurements are reported for both sampling from an isokinetic aerosol inlet and from a Counterflow Virtual Impactor (CVI, Brechtel Manufacturing Inc.). Users of these measurements are encouraged to consult with the authors about appropriate interpretation before submitting for publication, offering coauthorship where appropriate. 

Abstract. Acid–base clusters and stable salt formation are critical drivers of new particle formation events in the atmosphere. In this study, we explore salt heterodimer (a cluster of one acid and one base) stability as a function of gas-phase acidity, aqueous-phase acidity, heterodimer proton transference, vapor pressure, dipole moment and polarizability for salts comprised of sulfuric acid, methanesulfonic acid and nitric acid with nine bases. The best predictor of heterodimer stability was found to be gas-phase acidity. We then analyzed the relationship between heterodimer stability and J4×4, the theoretically predicted formation rate of a four-acid, four-base cluster, for sulfuric acid salts over a range of monomer concentrations from 105 to 109 molec cm−3 and temperatures from 248 to 348 K and found that heterodimer stability forms a lognormal relationship with J4×4. However, temperature and concentration effects made it difficult to form a predictive expression of J4×4. In order to reduce those effects, heterodimer concentration was calculated from heterodimer stability and yielded an expression for predicting J4×4 for any salt, given approximately equal acid and base monomer concentrations and knowledge of monomer concentration and temperature. This parameterization was tested for the sulfuric acid–ammonia system by comparing the predicted values to experimental data and was found to be accurate within 2 orders of magnitude. We show that one can create a simple parameterization that incorporates the dependence on temperature and monomer concentration on J4×4 by defining a new term that we call the normalized heterodimer concentration, Φ. A plot of J4×4 vs. Φ collapses to a single monotonic curve for weak sulfate salts (difference in gas-phase acidity >95 kcal mol−1) and can be used to accurately estimate J4×4 within 2 orders of magnitude in atmospheric models.