Size-resolved growth rates of freshly nucleated particles acquired from size distributions down to 1 nanometer

Description

Atmospheric aerosols influence climate and climate change on local to global scales by affecting the atmospheric radiation balance directly through scattering and absorbing incoming solar radiation and indirectly as cloud condensation nuclei (CCN). New particle formation (NPF) by photochemical reactions of gas-phase precursors greatly increases the number concentrations of atmospheric aerosols and is often followed by rapid growth to a CCN-active size, leading to a significant enhancement of the global CCN population. This rapid growth, often two to fifty times that of the growth assuming the condensation of sulfuric acid alone, is not well understood or represented in global models, limiting the ability to accurately assess the impact of NPF on the global surface CCN population and the aerosol indirect effect. Understanding this rapid particle growth and representing it in models requires direct measurements of the particle growth rate, especially immediately following nucleation, at which stage freshly nucleated particles are most vulnerable to scavenging by existing particles. Recently, size distribution measurements of freshly nucleated 1–6 nm particles were acquired during an intensive field campaign in Boulder, Colorado, using a diethylene glycol-based ultrafine condensation particle counter optimized for detection of 1-nm condensation nuclei as a detector in a scanning mobility particle spectrometer. These measurements provide one of the first direct measurements of size- and time-dependent particle growth rates of freshly nucleated particles. Observed growth rates for 1–6 nm particles were found to range from 1–30 times that assuming only sulfuric acid condensation, with these growth rate enhancements increasing approximately linearly with diameter below 3 nm.