Abstract
The growth of freshly formed aerosol particles can be the bottleneck in their survival to cloud condensation nuclei. It is therefore crucial to understand how particles grow in the atmosphere. Insufficient experimental data has impeded a profound understanding of nano-particle growth under atmospheric conditions. Here we study nano-particle growth in the CLOUD (Cosmics Leaving OUtdoors Droplets) chamber, starting from the formation of molecular clusters. We present measured growth rates at sub-3 nm sizes with different atmospherically relevant concentrations of sulphuric acid, water, ammonia and dimethylamine. We find that atmospheric ions and small acid-base clusters, which are not generally accounted for in the measurement of sulphuric acid vapour, can participate in the growth process, leading to enhanced growth rates. The availability of compounds capable of stabilizing sulphuric acid clusters governs the magnitude of these effects and thus the exact growth mechanism. We bring these observations into a coherent framework and discuss their significance in the atmosphere.
Highlights
The growth of freshly formed aerosol particles can be the bottleneck in their survival to cloud condensation nuclei
New-particle formation and subsequent cloud condensation nuclei (CCN) production is limited by the particle growth rate (GR) in the 1–3 nm diameter size range, rather than by the formation rate of molecular clusters, which are frequently present in the atmosphere[3,6,7,8]
Even though sulphuric acid vapour has been established as the main driving component for particle formation in the atmosphere[2,6,9,10], numerous field studies have shown that the growth rates often substantially exceed the predictions based on measured sulphuric acid concentrations, and the remaining fraction of growth has usually been attributed to condensation of low-volatility organic vapours[3,8,10,11,12,13]
Summary
The growth of freshly formed aerosol particles can be the bottleneck in their survival to cloud condensation nuclei. Even though sulphuric acid vapour has been established as the main driving component for particle formation in the atmosphere[2,6,9,10], numerous field studies have shown that the growth rates often substantially exceed the predictions based on measured sulphuric acid concentrations, and the remaining fraction of growth has usually been attributed to condensation of low-volatility organic vapours[3,8,10,11,12,13] This is supported by quantitative measurements of the particle composition in the size range above 10 nm (refs 13,14). To the best of our knowledge, this is the first time these phenomena have been observed and quantified in a controlled system, which is required for understanding their role in nature
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