Establishing predictive benchmarks for new particle formation in the atmosphere

As researchers strive to understand the impact aerosols have on climate change, new approaches must be taken to study and quantify new particle formation (NPF) – the formation of atmospheric trace gases into climatically-relevant particles that is irregular and difficult to monitor in the atmosphere. Kreinbihl et al. sought to understand NPF in a laboratory setting to optimize climate change models.

To do so, the authors established structural motifs present in small ammonium and aminium bisulfate clusters using a combination of infrared spectroscopy and mass spectrometry, and characterized the structural growth mechanisms of the clusters to develop predictive benchmarks for climate models.

“Combining infrared spectroscopy and mass spectrometry allows us to take well-resolved infrared spectra of small particles that are precisely selected for size and composition, allowing us to study each step along the growth pathway,” said author Christopher Johnson.

By measuring the infrared vibrational spectra in the small ammonium and aminium bisulfate clusters, the authors could identify specific structural features of the clusters responsible for their growth. During the process, the authors discovered a spectral marker for intermolecular bisulfate-bisulfate hydrogen bonds.

“The assignments of small, 1-2 nanometer clusters, taken together, are sufficient to explain the spectra of larger ammonium bisulfate particles up to at least the 100–200 nm range, establishing what we believe is a complete account of the structural motifs that are ubiquitous in much larger atmospheric particles,” said Johnson.

Future research will involve exploring the role of water in NPF. The authors have begun probing the spectroscopic features of hydrated clusters and the thermodynamics of water binding in relation to NPF.

Source: “Establishing the structural motifs present in small ammonium and aminium bisulfate clusters of relevance to atmospheric new particle formation,” by John J. Kreinbihl, Nicoline C. Frederiks, Sarah E. Waller, Yi Yang, and Christopher J. Johnson, Journal of Chemical Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0015094 .