Aggregation of small dust particles on bigger grains can increase significantly their area / mass ratio which leads to a more efficient cooling of the grains. See Stepnik et al. (2003) for a striking example of this effect.

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or equivalently that 99% of the values are between $\langle I\rangle-3\sigma$ and $\langle I\rangle+3\sigma$ .

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... CIB

Both processes being more Gaussian than the interstellar emission they have the effect of lowering the skewness and kurtosis mostly. This effect is more important at small scale and low brightness where the noise and CIB fluctuations are stronger with respect to interstellarfluctuations.

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