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  1. (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. 
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    Free, publicly-accessible full text available June 5, 2025
  2. 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. 
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    Free, publicly-accessible full text available April 5, 2025
  3. 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.

     
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    Free, publicly-accessible full text available March 13, 2025
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  6. While new particle formation events have been observed worldwide, our fundamental understanding of the precursors remains uncertain. It has been previously shown that small alkylamines and ammonia (NH 3 ) are key actors in sub-3 nm particle formation through reactions with acids such as sulfuric acid (H 2 SO 4 ) and methanesulfonic acid (CH 3 S(O)(O)OH, MSA), and that water also plays a role. Because NH 3 and amines co-exist in air, we carried out combined experimental and theoretical studies examining the influence of the addition of NH 3 on particle formation from the reactions of MSA with methylamine (MA) and trimethylamine (TMA). Experiments were performed in a 1 m flow reactor at 1 atm and 296 K. Measurements using an ultrafine condensation particle counter (CPC) and a scanning mobility particle sizer (SMPS) show that new particle formation was systematically enhanced upon simultaneous addition of NH 3 to the MSA + amine binary system, with the magnitude depending on the amine investigated. For the MSA + TMA reaction system, the addition of NH 3 at ppb concentrations produced a much greater effect ( i.e. order of magnitude more particles) than the addition of ∼12 000 ppm water (corresponding to ∼45–50% relative humidity). The effect of NH 3 on the MSA + MA system, which is already very efficient in forming particles on its own, was present but modest. Calculations of energies, partial charges and structures of small cluster models of the multi-component particles likewise suggest synergistic effects due to NH 3 in the presence of MSA and amine. The local minimum structures and the interactions involved suggest mechanisms for this effect. 
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