Size-Dependent Reactions of Ammonium Bisulfate Clusters with Dimethylamine

Abstract

The reaction kinetics of ammonium bisulfate clusters with dimethylamine (DMA) gas were investigated using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Clusters ranged in size from 1 to 10 bisulfate ions. Although displacement of the first several ammonium ions by DMA occurred with near unit efficiency, displacement of the final ammonium ion was cluster size dependent. For small clusters, all ammonium ions are exposed to incoming DMA molecules, allowing for facile exchange ("surface" exchange). However, with increasing cluster size, an ammonium ion can be trapped in an inaccessible region of the cluster ("core" exchange), thereby rendering exchange difficult. DMA was also observed to add onto existing dimethylaminium bisulfate clusters above a critical size, whereas ammonia did not add onto ammonium bisulfate clusters. The results suggest that as the cluster size increases, di-dimethylaminium sulfate formation becomes more favorable. The results of this study give further evidence to suggest that ambient sub-3 nm diameter particles are likely to contain aminium salts rather than ammonium salts.

On the composition of ammonia–sulfuric-acid ion clusters during aerosol particle formation

“…Specifically, growing ion clusters consisted of practically only dimethylamine and H 2 SO 4 , and particle formation rates were significantly enhanced. The enhancement of particle formation rates in those experiments was due to dimethylamine being a stronger base than NH 3 and consequently forming more stable bonds with H 2 SO 4 molecules, as has been shown both theoretically (e.g., Bzdek et al, 2010) and experimentally (e.g., Kurtén et al, 2008). The same reason can account for the observation (here, as in Almeida et al, 2013) that dimethylamine binds first to the sulfuric acid trimer anion, whereas NH 3 requires one more H 2 SO 4 in the cluster and binds first to the sulfuric acid tetramer anion.…”

“…The resultant dominant role of NH 3 in the growth of the clusters, as opposed to organic bases (amines or amides), is most likely due to the differences in respective contaminant-level concentrations ([NH 3 ] about 2 to 4 pptv, [C 2 H 7 N] < 1 pptv). Indeed, previous experimental studies on both positively and negatively charged dimethylamine-NH 3 -H 2 SO 4 clusters showed that dimethylamine molecules would quickly displace NH 3 molecules in these clusters already at low-pptv-level amine concentrations, whereas the opposite (displacement of dimethylamine by NH 3 molecules) does not occur even at much higher gasphase NH 3 concentrations (Bzdek et al, 2010;Bzdek et al, 2011).…”

New particle formation and growth from methanesulfonic acid, trimethylamine and water

“…22,[26][27][28] In addition, amines have been shown to displace NH 3 in sulfate particles and clusters. [42][43][44][45] Based on these results, small particles are more likely to be aminium salts even if ammonium salts are initially formed.…”

Single particle analysis of amines in ambient aerosol in Shanghai

“…[30] Many studies have been performed to explore the enhancement effect of amines in nucleation in competition with ammonia. [31][32][33][34][35][36][37][38][39][40][41][42] In the past two decades, on-line single particle mass spectrometry has made significant contributions to the studies of ambient aerosols. [43] Using this technique, the size and composition of many individual particles can be determined simultaneously with good time resolution, allowing particle composition to be correlated with rapid changes in environmental conditions.…”