Size resolved chemical composition of nanoparticles from reactions of sulfuric acid with ammonia and dimethylamine

Abstract

Nanoparticle formation and growth driven by acid-base chemistry was investigated by introducing gas-phase sulfuric acid (H 2 SO 4 ) with ammonia (NH 3 ) or dimethylamine (DMA) into a flow tube reactor. A thermal desorption chemical Ionization mass spectrometer was used to measure the sizeresolved chemical composition of H 2 SO 4 -DMA and H 2 SO 4 -NH 3 nanoparticles formed under dry conditions and at 60% relative humidity. In contrast with predictions for bulk aqueous systems, nanoparticles showed a strong size-dependent composition gradient and did not always reach a fully neutralized state in excess of gas-phase base. Smaller particles were more acidic, with an acid:base ratio of 0.7 ± 0.1 and 1.3 ± 0.3 for 8.6 and 9.5 nm H 2 SO 4 -DMA particles formed under dry and humid conditions, respectively, and 3.1 ± 0.6 and 3.4 ± 0.3 for 7.5 nm H 2 SO 4 -NH 3 particles formed under dry and humid conditions, respectively. The acidity of particles generally decreased as particles grew. H 2 SO 4 -DMA particles became fully neutralized as they grew to 14 nm, but H 2 SO 4 -NH 3 particles at 12 nm were still acidic and were never observed to reach bulk sample thermodynamic equilibrium for the experimental conditions in this study. Thermodynamic modeling demonstrated that the observed trends can be reproduced by modifying acid dissociation constants to minimize acid-base chemistry, which may be caused by steric or mixing effects, and by considering volatilization of the neutral base. ARTICLE HISTORY

New particle formation from sulfuric acid and ammonia: nucleation and growth model based on thermodynamics derived from CLOUD measurements for a wide range of conditions

“…Comparison between measured and modeled growth rates at small diameters (2 nm) in the acid-base system (sulfuric acid-dimethylamine and sulfuric acid-ammonia) indicates that water has no significant effect on particle growth . The same can be concluded for the sulfuric acid-ammonia system at larger diameters (∼ 10 nm; see Chen et al, 2018).…”

“…However, the involvement of ammonia in the formation of new particles at the relatively warm conditions close to the surface is not clear yet. A recent study indicates that ion-induced ternary nucleation can explain some new particle formation events in the boreal forest in Finland ; evidence that NH 3 is important in polluted boundary layer environments has been presented earlier (Chen et al, 2012). Most recently, Jokinen et al (2018) showed that ion-induced ternary nucleation is important in coastal Antarctica.…”

An Experimental and Modeling Study of Nanoparticle Formation and Growth from Dimethylamine and Nitric Acid

“…The concentration of HNO 3 vapor was estimated by assuming that it achieves its saturation vapor pressure prior to exiting the saturator. The inlet for this study was altered from the Chen et al study 23 by the addition of a movable, 1/8" OD stainless steel tube inserted into the inlet end of the flow tube ( Figure 1). The stainless-steel tube was capped, and the gaseous nitric acid containing N 2 entered the flow tube through slits cut out of the cap to promote mixing.…”

“…Recently, however, several studies have reported that particles composed of sulfuric acid and base have been observed to be more acidic in particle diameters smaller than 15 nm, 21,22 and in the specific case of H 2 SO 4 -DMA particles, they even become more basic under dry conditions at some sizes. 23 This disparity between the composition of clusters and nanoparticles in such acid−base systems warrants additional investigation. These prior studies examined trends in nanoparticle composition from reactions of bases with sulfuric acid, a low-volatility diprotic acid.…”

Novel ionization reagent for the measurement of gas‐phase ammonia and amines using a stand‐alone atmospheric pressure gas chromatography (APGC) source

“…38 Finally, particle-bound amines (aminium and ammonium ions) have been detected using thermal desorption chemical ionization mass spectrometry (TDCIMS), where the particles are collected onto the tip of a platinum wire followed by subsequent thermal desorption and ionization using water clusters formed using a 210 Po radioactive source. 12,39,40 Ambient ionization mass spectrometry methods have been exponentially growing over the past ten years due to their versatility, ease of use, reduced fragmentation due to 'soft' ionization mechanisms, and minimal sample preparation. 41 We report here studies of the use of NMP as a somewhat unconventional ambient ionization agent for ammonia and a series of amines.…”