Stable sulphate clusters as a source of new atmospheric particles

Abstract

The formation of new atmospheric particles with diameters of 3-10 nm has been observed at a variety of altitudes and locations. Such aerosol particles have the potential to grow into cloud condensation nuclei, thus affecting cloud formation as well as the global radiation budget. In some cases, the observed formation rates of new particles have been adequately explained by binary nucleation, involving water and sulphuric acid, but in certain locations--particularly those within the marine boundary layer and at continental sites--observed ambient nucleation rates exceed those predicted by the binary scheme. In these locations, ambient sulphuric acid (H2SO4) levels are typically lower than required for binary nucleation, but are sufficient for ternary nucleation (sulphuric acid-ammonia-water). Here we present results from an aerosol dynamics model with a ternary nucleation scheme which indicate that nucleation in the troposphere should be ubiquitous, and yield a reservoir of thermodynamically stable clusters 1-3 nm in size. We suggest that the growth of these clusters to a detectable size (> 3 nm particle diameter) is restricted by the availability of condensable vapour. Observations of atmospheric particle formation and growth from a continental and a coastal site support this hypothesis, indicating that a growth process including ternary nucleation is likely to be responsible for the formation of cloud condensation nuclei.

Observations of new particle formation and size distributions at two different heights and surroundings in subarctic area in northern Finland

“…[13] It has been suggested that 1 nm is the size of a thermodynamically stable clusters, which under certain conditions grow to detectable sizes [Kulmala et al, 2000]. For this reason, the approximate starting time of formation of 1-nm particles was calculated.…”

Size and composition measurements of background aerosol and new particle growth in a Finnish forest during QUEST 2 using an Aerodyne Aerosol Mass Spectrometer

“…For instance, the number concentrations of atmospheric particles affects the microphysics of clouds, which may affect their rainfall, lifetime and optical properties and in turn, global climate (Penner et al, 2001;Twomey, 1977). In addition to mechanical and combustion processes, new particles can be created from the nucleation of gas phase species (Kulmala et al, 2000;Kulmala, 2003). These events have been observed in a variety of environments worldwide and may be a significant factor in the repopulation of particle numbers lost through deposition.…”

“…It is thought that in this particular environment, the biogenic VOCs and their oxidation products are responsible for the growth of the particles, although the initial formation is thought to happen though the nucleation of sulphuric acid with water and/or ammonia (Kulmala et al, 2000). For a detailed study into the initial nucleation and early stages of growth during this study, the reader is directed to Kulmala et al (2004a).…”

Deep convection as a source of new particles in the midlatitude upper troposphere

“…While conditions necessary for homogeneous nucleation do occur in the atmosphere, observations suggest that in some cases, new particles form more readily than models can predict for the homogeneous nucleation of sulfuric acid and water alone [Weber et al, 1995[Weber et al, , 1997. Thus other species, including ammonia and organic vapors, may participate in nucleation of new particles in some parts of the atmosphere [e.g., Ball et al, 1999;Kulmala et al, 2000].…”