Atmos. Chem. Phys. Discuss., 13, 14115-14140, 2013
www.atmos-chem-phys-discuss.net/13/14115/2013/
doi:10.5194/acpd-13-14115-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Identification and quantification of particle growth channels during new particle formation
M. R. Pennington1, B. R. Bzdek1, J. W. DePalma1, J. N. Smith2,3, A.-M. Kortelainen3, L. Hildebrandt Ruiz2,*, T. Petäjä4, M. Kulmala4, D. R. Worsnop4, and M. V. Johnston1
1Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
2Atmospheric Chemistry Division, National Center for Atmospheric Research, 1850 Table Mesa Dr., Boulder, CO 80305, USA
3Department of Applied Physics, University of Eastern Finland, Kuopio, 70211, Finland
4Department of Physical Sciences, University of Helsinki, 00014, Helsinki, Finland
*now at: Department of Chemical Engineering, University of Texas at Austin, Austin, TX 78712, USA

Abstract. Atmospheric new particle formation (NPF) is a key source of ambient ultrafine particles that may contribute substantially to the global production of cloud condensation nuclei (CCN). While NPF is driven by atmospheric nucleation, its impact on CCN concentration depends strongly on atmospheric growth mechanisms since the growth rate must exceed the loss rate due to scavenging in order for the particles to reach the CCN size range. In this work, chemical composition measurements of 20 nm diameter particles during NPF in Hyytiälä, Finland, in March–April 2011 permit identification and quantitative assessment of important growth channels. In this work we show that: (A) sulfuric acid, a key species associated with atmospheric nucleation, accounts for less than half of particle mass growth during this time period; (B) the sulfate content of a growing particle during NPF is quantitatively explained by condensation of gas phase sulfuric acid molecules, in other words sulfuric acid uptake is collision limited; (C) sulfuric acid condensation substantially impacts the chemical composition of preexisting nanoparticles before new particles have grown to a size sufficient to be measured; (D) ammonium and sulfate concentrations are highly correlated, indicating that ammonia uptake is driven by sulfuric acid uptake; (E) sulfate neutralization by ammonium does not reach the predicted thermodynamic endpoint, suggesting that a kinetic barrier exists for ammonia uptake; (F) carbonaceous matter accounts for more than half of the particle mass growth and its oxygen-to-carbon ratio (~0.5) is characteristic of freshly formed secondary organic aerosol; and (G) differences in the overall growth rate from one formation event to another are caused by variations in the growth rates of all major chemical species, not just one individual species.

Citation: Pennington, M. R., Bzdek, B. R., DePalma, J. W., Smith, J. N., Kortelainen, A.-M., Hildebrandt Ruiz, L., Petäjä, T., Kulmala, M., Worsnop, D. R., and Johnston, M. V.: Identification and quantification of particle growth channels during new particle formation, Atmos. Chem. Phys. Discuss., 13, 14115-14140, doi:10.5194/acpd-13-14115-2013, 2013.
 
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