Size-Resolved Chemical Composition of Sub-20 nm Particles from Methanesulfonic Acid Reactions with Methylamine and Ammonia

Abstract

Particle formation in the atmosphere from gas-phase precursors has been observed around the world; however, our fundamental understanding of the key species responsible and mechanisms involved remains uncertain. Recent laboratory studies demonstrated that acid–base reactions involving methanesulfonic acid (CH3SO3H, MSA) and small alkylamines may contribute significantly to new particle formation. To date, most of the investigations have been focused on particle number concentration and size distribution measurements in combination with quantum chemistry predictions of the most stable clusters. Here, we present the first measurements of the size-resolved chemical composition of sub-20 nm particles generated in a custom flow reactor from the reaction of MSA with methylamine (MA) in the presence or absence of NH3 using thermal desorption chemical ionization mass spectrometry (TDCIMS). A novel design of the TDCIMS inlet was evaluated, and the measurement of the chemical composition of particles was extended down to 5 nm in diameter, the smallest size yet reported for this method. MSA–MA particles with diameters smaller than 9 nm were found to be more acidic, with an acid/base molar ratio of 1.8 ± 0.4 (1σ) for 5 nm particles compared to the larger particles which were neutral. A similar acid/base molar ratio trend was observed when NH3 was added to the MSA–MA combination. In the MSA–MA–NH3 system, the MA/NH3 molar ratio was higher than 1 (up to 2.6) for all particle sizes despite the much larger concentration of NH3 in the gas phase (the gas-phase MA/NH3 ratio was ∼0.23), indicating that MA is a key component in particle formation from this system. The potential reasons for this based on previous calculations of small clusters in this system are discussed.

Open questions on the chemical composition of airborne particles

“…Commonly used ionization reagents include protons in the positive ion mode and O 2 − , iodide, nitrate, and CF 3 O − ions in the negative ion mode. Some more exotic reagents such as N-methyl-2-pyrrolidone have been recently used for measurement of species that can be difficult to detect such as ammonia in nanoparticles 13 . The use of elemental analysis with high-resolution techniques and factor analysis of mass spectra has notably increased our understanding of particle sources, level of oxidation, and the ubiquity of organic aerosol in air 3 .…”

“…2a 3 × 10 11 molecules cm −3 ) and methylamine (MA; 1.4 × 10 11 molecules cm −3 ) under dry conditions. Particles were sampled at 0.6 s and 9 s residence time, respectively, using a thermal desorption chemical ionization mass spectrometer 13 ; b size distributions of monodisperse 220 nm glutaric acid particles coated with malonic acid with coating thickness shown on top axis and c ratio of malonic acid (coating) signal to glutaric acid (core) signal detected for the particles in b using sonic spray ionization mass spectrometry 16 .…”

“…COMMUNICATIONS CHEMISTRY | https://doi.org/10.1038/s42004-020-00347-4 COMMENT COMMUNICATIONS CHEMISTRY | (2020) 3:108 | https://doi.org/10.1038/s42004-020-00347-4 | www.nature.com/commschem shows the acid:base molar ratio for nanoparticles formed from the gas phase reaction of methanesulfonic acid with methylamine, where the smallest particles (<9 nm) contain more acid than base 13 . The capability of measuring chemical composition down to~1 nm is crucial for understanding how stable clusters form and subsequently grow to detectable particles.…”

The Role of Organic Acids in New Particle Formation from Methanesulfonic Acid and Methylamine

“…Atmospheric bases can enhance both SA-driven and MSA-driven NPF by stabilizing freshly formed molecular clusters via acid-base proton transfer reactions (Zhang et al, 2012;Almeida et al, 2013;Chen et al, 2020b;Perraud et al, 2020b;Perraud et al, 2020a;Kurten et al, 2008;Loukonen et al, 2010;Glasoe et al, 2015;Olenius et al, 2017;Ma et al, 2019b;Zuo et al, 2021;Shen et al, 2020;Shen et al, 2019;Chen et al, 2020a;Xu et al, 2020;Nishino et al, 2014). Amines have been shown to be much more efficient stabilizing species compared to ammonia for both SA-base and MSA-base cluster formation (Almeida et al, 2013;Kurten et al, 2008;Chen et al, 2020b;Perraud et al, 2020a;Shen et al, 2020;Chen et al, 2016).…”

Comment on acp-2021-831

“…Atmospheric bases can enhance both SA-driven and MSA-driven NPF by stabilizing freshly formed molecular clusters via acid-base proton transfer reactions (Zhang et al, 2012;Almeida et al, 2013;Chen et al, 2020b;Perraud et al, 2020b;Perraud et al, 2020a;Kurten et al, 2008;Loukonen et al, 2010;Glasoe et al, 2015;Olenius et al, 2017;Ma et al, 2019b;Zuo et al, 2021;Shen et al, 2020;Shen et al, 2019;Chen et al, 2020a;Xu et al, 2020;Nishino et al, 2014). Amines have been shown to be much more efficient stabilizing species compared to ammonia for both SA-base and MSA-base cluster formation (Almeida et al, 2013;Kurten et al, 2008;Chen et al, 2020b;Perraud et al, 2020a;Shen et al, 2020;Chen et al, 2016).…”