Kristensen, Thomas Bjerring9; Wex, Heike3; Nekat, Bettina3; Nøjgaard, Jacob Klenø4; Pinxteren, Dominik van3; Lowenthal, Douglas H.5; Mazzoleni, Lynn R.10; Dieckmann, Katrin3; Bender Koch, Christian11; Mentel, Thomas F.8; Herrmann, Hartmut3; Hallar, A. Gannet5; Stratmann, Frank3; Bilde, Merete9
1 Department of Chemistry, Faculty of Science, Københavns Universitet2 Environmental Chemistry and Physics, Department of Basic Sciences and Environment, Faculty of Life Sciences, Københavns Universitet3 Leibniz Institute for Tropospheric Research4 Institut for Miljøvidenskab - Environmental social science5 Desert Research Institute6 Michigan Technological University7 Administration, Department of Chemistry, Faculty of Science, Københavns Universitet8 Research Center Jülich GmbH9 Department of Chemistry, Faculty of Science, Københavns Universitet10 Michigan Technological University11 Administration, Department of Chemistry, Faculty of Science, Københavns Universitet
Humic-like substances (HULIS) constitute a significant fraction of aerosol particles in different environments. Studies of the role of HULIS in hygroscopic growth and cloud condensation nuclei (CCN) activity of aerosol particles are scarce, and results differ significantly. In this work the hygroscopic growth and CCN activity of water extracts (WE) and HULIS extracted from particulate matter (PM) collected at a polluted urban site (Copenhagen, Denmark), a rural site (Melpitz, Germany) and the remote site Storm Peak Laboratory (Colorado, USA) were investigated. Measurements of inorganic ions, elemental carbon, organic carbon and water soluble organic carbon (WSOC) within the PM confirmed that the sources of aerosol particles most likely differed for the three samples. The hygroscopic properties of the filtered WE were characterized by hygroscopicity parameters for subsaturated conditions (k(GF)) of 0.25, 0.41 and 0.22, and for supersaturated conditions k(CCN) were 0.23, 0.29 and 0.22 respectively for the urban, rural and remote WE samples. The measured hygroscopic growth and CCN activity were almost identical for the three HULIS samples and could be well represented by k(GF) = 0.07 and k(CCN) = 0.08-0.10 respectively. Small amounts of inorganic ions were present in the HULIS samples so the actual values for pure HULIS are expected to be slightly lower (k(GF)(*) = 0.04-0.06 and k(CCN)(*) = 0.07-0.08). The HULIS samples are thus less hygroscopic compared to most previous studies. To aid direct comparison of hygroscopic properties of HULIS from different studies, we recommend that the fraction of inorganic species in the HULIS samples always is measured and reported.
Journal of Geophysical Research, 2012, Vol 117, Issue D22, 27