2017, Heintzenberg, Jost, Leck, Caroline, Birmili, Wolfram, Wehner, Birgit, Tjernström, Michael, Wiedensohler, Alfred

The present study covers submicrometer aerosol size distribution data taken during three Arctic icebreaker expeditions in the summers of 1991, 1996 and 2001. The size distributions of all expeditions were compared in log-normally fitted form to the statistics of the marine number size distribution provided by Heintzenberg et al. (2004) yielding rather similar log-normal parameters of the modes. Statistics of the modal concentrations revealed strong concentration decreases of large accumulation mode particles with increasing length of time spent over the pack ice. The travel-time dependencies of both Aitken and ultrafine modes strongly indicate, as other studies did before, the occurrence of fine-particle sources in the inner Arctic. With two approaches evidence of fog-related aerosol source processeswas sought for in the data sets of 1996 and 2001 because they included fog drop size distributions. With increasing fog intensity modes in interstitial particle number concentrations appeared in particular in the size range around 80 nm that was nearly mode free in clear air. A second, dynamic approach revealed that Aitken mode concentrations increased strongly above their respective fog-period medians in both years before maximum drop numbers were reached in both years. We interpret the results of both approaches as strong indications of fog-related aerosol source processes as discussed in Leck and Bigg (1999) that need to be elucidated with further data from dedicated fog experiments in future Arctic expeditions in order to understand the life cycle of the aerosol over the high Arctic pack ice area.

2016, Russell, Philip B., Heintzenberg, Jost

As 1 of 6 focused ACE-2 activities, a clear sky column closure experiment (CLEARCOLUMN) took place in June/July 1997 at the southwest corner of Portugal, in the Canary Islands, and over the eastern Atlantic Ocean surrounding and linking those sites. Overdetermined sets of volumetric, vertical profile and columnar aerosol data were taken from the sea surface to~5 km asl by samplers and sensors at land sites (20–3570 m asl), on a ship, and on 4 aircraft. In addition, 5 satellites measured upwelling radiances used to derive properties of the aerosol column. Measurements were made in a wide range of conditions and locations (e.g., the marine boundary layer with and without continental pollution, the free troposphere with and without African dust). Numerous tests of local and column closure, using unidisciplinary and multidisciplinary approaches, were conducted. This paper summarizes the methodological approach, the experiment sites and platforms, the types of measurements made on each, the types of analyses conducted, and selected key results, as a guide to the more complete results presented in other papers in this special issue and elsewhere. Example results include determinations of aerosol single scattering albedo by several techniques, measurements of hygroscopic effects on particle light scattering and size, and a wide range in the degree of agreement found in closure tests. In general, the smallest discrepancies were found in comparisons among (1) different techniques to measure an optical property of the ambient, unperturbed aerosol (e.g., optical depth, extinction, or backscatter by sunphotometer, lidar, and/or satellite) or (2) different techniques to measure an aerosol that had passed through a common sampling process (e.g., nephelometer and size spectrometer measurements with the same or similar inlets, humidities and temperatures). Typically, larger discrepancies were found between techniques that measure the ambient, unperturbed aerosol and those that must reconstruct the ambient aerosol by accounting for (a) processes that occur during sampling (e.g., aerodynamic selection, evaporation of water and other volatile material) or ( b) calibrations that depend on aerosol characteristics (e.g., sizedependent density or refractive index). A primary reason for the discrepancies in such cases is the lack of validated hygroscopic growth models covering the necessary range of particle sizes and compositions. Other common reasons include (1) using analysis or retrieval techniques that assume aerosol properties (e.g., density, single scattering albedo, shape) that do not apply in all cases and (2) using surface measurements to estimate column properties. Taken together, the ACE-2 CLEARCOLUMN data set provides a large collection of new information on the properties of the aerosol over the northeast Atlantic Ocean. CLEARCOLUMN studies have also pointed to improved techniques for analyzing current and future data sets (including satellite data sets) which will provide a more accurate and comprehensive description of the Atlantic–European–African aerosol. Thus they set the stage for an improved regional quantification of radiative forcing by anthropogenic aerosols.