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Products of the oxidation of BTH by OH in air. 

Description: Mechanistic analysis of ion desorption from glutaric acid particles used in the development of surface-sensitive mass spectroscopy ionization methods. Abstract: Ionization via desorption of charged analytes from the surface of solid amorphous glutaric acid particles, without the assistance of an external energy source, has been shown to be a promising method that can be coupled to mass spectrometry. We conduct mechanistic studies of the later stages of this ionization process using atomistic molecular dynamics. Our analysis focuses on the hydrogen bonding, diffusion, and ion desorption from nano-aggregates of glutaric acid. These nano-aggregates exhibit an extended H-bonded network, often comprising H-bonded chains, linear dimeric assemblies, and occasionally cyclic trimeric assemblies. These local structures serve as centers for proton transfer reactions. The intermediate hydrocarbon chain between the proton-carrying oxygen sites prevents proton diffusion over a long distance unless there is significant translational or rotational movement of the proton-carrying diacid molecule. Our calculations show that diffusion on the surface is an order of magnitude faster than in the core of the nano-aggregate, which aids effective proton transfer on the particle's exterior. We find that ionic species desorb from the aggregate's surface through independent evaporation events of small clusters, where the ion is coordinated by only a few glutaric acid molecules. Near the nano-aggregate's Rayleigh limit, jets capable of releasing multiple ions were not observed. These observations suggest a more general ion-evaporation mechanism that applies to low-dielectric particles of various sizes, complementing the original ion-evaporation mechanism proposed for aqueous droplets with an approximate radius of 10–15 nm. The combined evidence from molecular modeling presented here and the thermodynamic properties of solid and supercooled liquid glutaric acid indicates that the stronger signals of glutaric acid observed in the mass spectra, relative to other experimentally tested diacids, can be attributed to its significantly lower melting point and the reduced enthalpy of vaporization of its amorphous state compared to other tested diacids. 

(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. 

Emerging contaminants (EC) distributed on surfaces in the environment can be oxidized by gas phase species (top–down) or by oxidants generated by the underlying substrate (bottom–up). One class of EC is the neonicotinoid (NN) pesticides that are widely distributed in air, water, and on plant and soil surfaces as well as on airborne dust and building materials. This study investigates the OH oxidation of the systemic NN pesticide acetamiprid (ACM) at room temperature. ACM on particles and as thin films on solid substrates were oxidized by OH radicals either from the gas phase or from an underlying TiO₂or NaNO₂substrate, and for comparison, in the aqueous phase. The site of OH attack is both the secondary >CH₂group as well as the primary –CH₃group attached to the tertiary amine nitrogen, with the latter dominating. In the case of top–down oxidation of ACM by gas phase OH radicals, addition to the –CN group also occurs. Major products are carbonyls and alcohols, but in the presence of sufficient water, their hydrolyzed products dominate. Kinetics measurements show ACM is more reactive toward gas phase OH radicals than other NN nitroguanidines, with an atmospheric lifetime of a few days. Bottom–up oxidation of ACM on TiO₂exposed to sunlight outdoors (temperatures were above 30 °C) was also shown to occur and is likely to be competitive with top–down oxidation. These findings highlight the different potential oxidation processes for EC and provide key data for assessing their environmental fates and toxicologies. 

Adsorption of organics on surfaces is important in both outdoor and indoor environments. Surfaces can serve as sinks for gas-phase species, act as reservoirs by emitting previously partitioned organics back into the gas phase, and can facilitate heterogeneous chemistry. We report here studies of the uptake and desorption energetics of gas-phase limonene, a volatile and widely-distributed monoterpene, on solid silica nanoparticles using a unique apparatus that allows for temperature programmed desorption (TPD) measurements of surface binding energies as well as Knudsen cell gas uptake measurements. A multiphase kinetic model was applied to these data to provide additional molecular-level understanding of the processes involved. TPD experiments yielded an average desorption energy of 47.5 ± 8.2 kJ mol-1 (±1s, sample standard deviation), the first direct experimental measurement of this parameter over a broad temperature range (150–320 K). Initial net uptake coefficients (0,net) range from (1.7 ± 0.3) ×10-3 (±1s) at 210 K to (2.3 ± 0.4) ×10-4 (±1s) at 250 K, reflecting increased rates of desorption with an increase in temperature combined with increased rates of diffusion and re-adsorption within the pores between adjacent silica nanoparticles. Effective Langmuir constants, which also reflect the effects of pore diffusion and re-adsorption, were determined from the uptake data and vary from (1.8–0.3)×10-13 cm3 molecule-1 over the same temperature range. These results are in excellent agreement with previous studies around room temperature and with theoretical calculations of the energetics of the limonene-silica interaction. The strong attraction between limonene and the polar silica surface shows the importance of including such interactions in models of the atmospheric fates of terpenes both indoors and outdoors. 

 

Ozonolysis of model nitrogen-containing alkenes shows a wide range of reactivity and formation of toxic products.