(Invited Speaker) New Particle Formation: Atmospheric and Laboratory Evidence for Chemical Nucleation of Sulfuric Acid and Amines

Observations throughout the troposphere have shown that new particle formation (NPF) occurs every few days. These freshly nucleated particles often grow large enough to significantly affect the concentrations of cloud condensation nuclei (CCN) during the course of a day, thereby impacting climate. Early studies suggested that NPF was unlikely to be a significant process in the atmosphere. Recent work has shown that NPF is significant because both nucleation and growth rates are much higher than can be explained by known processes. We recently discovered that amines significantly enhance nucleation rates in the presence of sulfuric acid, which apparently contributes to the high atmospheric nucleation rates that are observed. These discoveries were enabled by measurements with three new prototype instruments: (1) the Cluster CIMS for measuring neutral molecular clusters formed by nucleation (Zhao et al. 2010), (2) the DEG SMPS for measuring aerosol size distributions down to about 1 nm (Jiang et al. 2010), and (3) the ambient pressure proton transfer mass spectrometer (Amp-MS) for measuring concentrations of amines. The ambient measurements that will be discussed were carried out in Atlanta during the summer of 2009. Those observations motivated laboratory studies, which will also be discussed.

Atmospheric measurements showed that the concentrations of molecular clusters formed by nucleation (e.g., clusters containing 3 or 4 sulfuric acid molecules) increased with increasing concentrations of amines. Laboratory chamber studies with dimethyl amine and sulfuric acid showed a similar trend. Nucleation rates estimated from these measurements showed a clear dependence on the concentrations of both sulfuric acid and amines. Implications of this work on atmospheric nucleation rates will be discussed.

Jiang, J., J. Zhao, M. Chen, J. Scheckman, B. J. Williams, C. Kuang, F. L. Eisele and P. H. McMurry (2010). "First Measurements of Atmospheric Neutral Cluster and 1-2 nm Particle Size Number Distributions During Nucleation Events." Aerosol Science and Technology, in press.

Zhao, J., F. L. Eisele, M. Titcombe, C. Kuang and P. H. McMurry (2010). "Chemical Ionization Mass Spectrometric Measurements of Atmospheric Neutral Clusters using the Cluster-CIMS " Journal of Geophysical Research 115: D08205. doi: 10.1029/2009JD012606.