CCN activation of fumed silica aerosols mixed with soluble pollutants

• Main Authors: Dalirian, M., Keskinen, H., Ahlm, L., Ylisirnio, A., Romakkaniemi, S., Laaksonen, A., Virtanen, A., Riipinen, I.
• Other Authors: Department of Physics
• Format: Article in Journal/Newspaper
• Language: English
• Published: COPERNICUS GESELLSCHAFT MBH 2016
• Subjects: CONDENSATION NUCLEI ACTIVITY; PARTICULATE AIR-POLLUTION; FRACTAL-LIKE DIMENSION; REGIONAL DUST SAMPLES; DROPLET ACTIVATION; HYGROSCOPIC GROWTH; PARTICLE DENSITY; ATMOSPHERIC MEASUREMENTS; DIFFERENTIAL MOBILITY; INSOLUBLE PARTICLES; 114 Physical sciences; Arctic
• Online Access: http://hdl.handle.net/10138/161556

Particle-water interactions of completely soluble or insoluble particles are fairly well understood but less is known of aerosols consisting of mixtures of soluble and insoluble components. In this study, laboratory measurements were performed to investigate cloud condensation nuclei (CCN) activity of silica particles mixed with ammonium sulfate (a salt), sucrose (a sugar) and bovine serum albumin known as BSA (a protein). The agglomerated structure of the silica particles was investigated using measurements with a differential mobility analyser (DMA) and an aerosol particle mass analyser (APM). Based on these data, the particles were assumed to be compact agglomerates when studying their CCN activation capabilities. Furthermore, the critical super-saturations of particles consisting of pure and mixed soluble and insoluble compounds were explored using existing theoretical frameworks. These results showed that the CCN activation of single-component particles was in good agreement with Kohler- and adsorption theory based models when the agglomerated structure was accounted for. For mixed particles the CCN activation was governed by the soluble components, and the soluble fraction varied considerably with particle size for our wet-generated aerosols. Our results confirm the hypothesis that knowing the soluble fraction is the key parameter needed for describing the CCN activation of mixed aerosols, and highlight the importance of controlled coating techniques for acquiring a detailed understanding of the CCN activation of atmospheric insoluble particles mixed with soluble pollutants. Peer reviewed