On the contribution of Aitken mode particles to cloud droplet populations at continental background areas – a parametric sensitivity study

[摘要] Aitken mode particles are potentially an important sourceof cloud droplets in continental background areas. In order to find outwhich physico-chemical properties of Aitken mode particles are mostimportant regarding their cloud-nucleating ability, we calculated the numberof cloud droplets formed on Aitken mode particles, CD₂, with an adiabaticair parcel model. The model output was analyzed using a global sensitivityanalysis method that quantifies and ranks the relative importance of theconsidered input parameters to the total variance of CD₂. The resultsshow that unless the particle surface tension or the mass accommodationcoefficient of water is strongly reduced due to the presence ofsurface-active organics, the parameters describing the size distribution aregenerally more important than the particle chemical composition. In theabsence of such compounds, the chemical composition may have roughly anequal importance with the size distribution only at low updraft velocitiescharacterized by maximum supersaturations below 0.1%. Furthermore, thelargest source of variability is generally the particle numberconcentration, followed by the particle size. The performed sensitivityanalysis revealed that the variability of the particle chemical compositionmay dominate the total variation of CD₂ if: 1) the value of α varies atleast one order of magnitude more than what is expected for pure watersurfaces (10⁻²–1), or 2) the particle surface tension varies more thanroughly 30% under conditions close to reaching saturation.

[学科分类] 大气科学