Identification and quantification of particle growth channels during new particle formation

Abstract

New particle formation (NPF) in the atmosphere substantially impacts ultrafine particle number concentrations and cloud condensation nuclei (CCN) levels. The impact of NPF on CCN levels depends on the ability of the particles to grow rapidly into the CCN size range thus avoiding loss due to scavenging. This work presents quantitative chemical composition measurements of individual 20 nm diameter particles during NPF using the Nano Aerosol Mass Spectrometer (NAMS). Sulfuric acid is shown to contribute quantitatively to changes in the sulfate mass fraction. However, growth due to sulfuric acid generally accounts for <50% of the total particle growth. Ammonium and sulfate are highly correlated, but sulfuric acid is not neutralized to its thermodynamic endpoint. Carbonaceous matter accounts for >50% of mass growth and is characteristic of fresh secondary organic aerosol. Differences in the overall growth rate from one event to another are caused by variations among all major chemical species and not just one individual species. © 2013 AIP Publishing LLC.