The Importance of Neutrality

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Science  05 Oct 2007:
Vol. 318, Issue 5847, pp. 13c
DOI: 10.1126/science.318.5847.13c

Atmospheric aerosol particles, which have diameters between 3 and 10 nanometers (nm), are formed continually in all parts of the troposphere. These particles play key roles in climate because they can absorb or reflect sunlight and affect cloud formation and atmospheric chemical reactions. However, how and in what quantities aerosols form are poorly understood, largely because of the difficulty in observing the smaller particles from which they grow. Kulmala et al. (p. 89, published online 30 August) investigated the distribution of particles smaller than 3 nm in diameter and found that an abundant pool of neutral clusters is present at almost all times. These clusters dominate the process of atmospheric aerosol formation, at least over boreal forests. These findings dispel the suggestion that aerosol production is driven mainly by processes involving ion clusters.

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