Is atmospheric aerosol an aerosol?--a look at sources and variability.

Countless observations of the atmospheric aerosol reveal large concentration variabilities. Such variability is not characteristic for a colloid. It must have a certain degree of stability and that is not seen in the atmospheric aerosol. The question then is open if the atmospheric aerosol is really a colloid, an aerosol. On the other side, the atmospheric aerosol exhibits typical properties of colloids, which mainly stem from the large surface-to-volume ratio. This discrepancy is dissolved if the residence time of the aerosol particles is taken into account. This results in a more or less dynamic equilibrium. Because the residence time of the atmospheric aerosol is size dependent, sources (and sinks) have size dependent productions (removals). For the first time the paper presents data for selected atmospheric model aerosols, at which size ranges the majority of particles (whether mass or number) are produced (and removed). The results are also pointing toward cloud droplet residues as a supplementary aerosol particle source. In addition, the size dependent variability is asking for a change in measuring strategy and instrumental design. Short residence times require good time resolution. The paper shows that size ranges below .01 and above .1 microm are most susceptible to measurements with low time resolution. Present day measuring methods often lack the necessary time resolution.