Global distribution of the effective aerosol hygroscopicity parameter for CCN activation

By K. Pringle, H. Tost, A. Pozzer, Ulrich Pöschl, J. Lelieveld. 2010

264 citations recorded by the source corpus.

Abstract. In this study we use the ECHAM/MESSy Atmospheric Chemistry (EMAC) model to simulate global fields of the effective hygroscopicity parameter κ which approximately describes the influence of chemical composition on the cloud condensation nucleus (CCN) activity of aerosol particles. The obtained global mean values of κ at the Earth's surface are 0.27±0.21 for continental and 0.72±0.24 for marine regions (arithmetic mean ± standard deviation). These values are the internally mixed κ calculated across the Aitken and accumulation modes. The mean κ values are in good agreement with previous estimates based on observational data, but the model standard deviation for continental regions is higher. Over the continents, the regional distribution appears fairly uniform, with κ values mostly in the range of 0.1–0.4. Lower values over large arid regions and regions of high organic loading lead to reduced continental average values for Africa and South America (0.15–0.17) compared to the other continents (0.21–0.36). Marine regions show greater variability with κ values ranging from 0.9–1.0 in remote regions to 0.4–0.6 in continental outflow regions where the highly hygroscopic sea spray aerosol mixes with less hygroscopic continental aerosol. Marine κ values as low as 0.2–0.3 are simulated in the outflow from the Sahara desert. At the top of the planetary boundary layer the κ values can deviate substantially from those at the surface (up to 30%) – especially in marine and coastal regions. In moving from the surface to the height of the planetary boundary layer, the global average marine κ value reduces by 20%. Thus, surface observations may not always be representative for the altitudes where cloud formation mostly occurs. In a pre-industrial model scenario, the κ values tend to be higher over marine regions and lower over the continents, because the anthropogenic particulate matter is on average less hygroscopic than sea-spray but more hygroscopic than the natural continental background aerosol (dust and organic matter). In regions influenced by desert dust the particle hygroscopicity has increased strongly as the mixing of air pollutants with mineral particles typically enhances the κ values by a factor of 2–3 above the initial value of ≈0.005.

Subfields: Atmospheric Science, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/c0a90cedad283c345adff8325b4fb88ef2f76376

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Citations in the corpus

On the effect of dust particles on global cloud condensation nuclei and cloud droplet number (2011, background): “…the dust impacts on cloud droplet number assume that dust acts as CCN only when soluble material exists in the particles (and controls its hygroscopicity) [e.g., Hoose et al., 2008b; Kelly et al., 2007; Lee et al., 2009; Manktelow et al., 2010; Pringle et al., 2010a, 2010b; Solomos et al., 2011].”
Cloud condensation nuclei production associated with atmospheric nucleation: a synthesis based on existing literature and new results (2012, methodology): “(1) provides relatively accurate link between the particle size, its chemical composition and CCN activity (Petters and Kreidenweis, 2007; Pringle et al., 2010 and references therein; Rissler et al., 2010).”