How cells acquire complex shapes is a fundamental question in biology. Lauster et al. show that PHGAP/RENs associate with cortical microtubules preferentially along anticlinal cell faces, and they facilitate the spatially distinct deactivation of ROP2 in indentations. This interplay is essential for multipolarity of epidermal pavement cells.

Abstract. Thermal–optical measurement techniques are widely used to classify carbonaceous material. The results of different methods for total carbon are comparable but can vary by >44 % for elemental carbon. One major cause of variation is the formation of pyrolyzed carbon during the heating process which occurs mainly in samples with a high amount of brown carbon (BrC). In this study the structural changes of two different CAST (combustion aerosol standard) aerosol samples caused by the heating procedure in a thermal–optical instrument were investigated with UV–VIS and Raman spectroscopy, the integrating-sphere technique (IS) and transmission electron microscopy. All analysis techniques showed significant structural changes for BrC-rich samples at the highest temperature level (870 ∘C) in helium. The structure of the heated BrC-rich sample resembles the structure of an unheated BrC-poor sample. Heating the BrC-rich sample to 870 ∘C increases the graphitic domain size within the material from 1.6 to 2 nm. Although the Raman spectra unambiguously show this increase in ordering only at the highest temperature step, UV–VIS and IS analyses show a continuous change in the optical properties also at lower temperatures. The sample with a negligible amount of BrC, however, did not show any significant structural changes during the whole heating procedure.

Steam collection devices collecting aerosol particles into liquid samples are frequently used to analyze water-soluble particulate material. The fate of water-insoluble components is often neglected. In this work, we show that fresh soot particles can be suspended into pure water using a steam collection device, the particle-into-liquid sampler (PILS, Weber et al. 2001). The overall collection efficiency of freshly generated soot particles was found to be on the order of 20%. This shows that, depending on the analytic technique employed, the presence of insoluble, and/or hydrophobic particles in liquid samples from steam collection cannot be neglected. Copyright © 2018 The Author(s). Published with license by Taylor & Francis Group, LLC

Abstract. Thermal–optical measurement techniques are widely used for the monitoring of carbonaceous aerosols. Although results of different thermal–optical measurement techniques are comparable for total carbon, they can vary widely for values of elemental carbon especially in the presence of brown carbon. Charring of organic material during the inert heating phase of thermal–optical measurements has been found to be a major confounder, but no literature about investigations of structural changes during this process in atmospheric aerosols is available. In a recent study we investigated these structural changes for combustion aerosol standard (CAST) soot. Now we apply this approach to selected atmospheric aerosol filter samples and a subset of eight washed filter samples with low loadings of water-soluble organic carbon (WSOC). To investigate structural changes, Raman spectra were obtained for samples heated to the corresponding temperature levels and gas atmospheres of the EUSAAR2 and NIOSH870 protocols. The temperature levels where changes in the Raman spectra occurred (i.e., changes in structure) varied for different samples. For the washed samples with low WSOC loadings and absence of other water-soluble aerosol components such as inorganic salts, changes in structural ordering and darkening of the samples were not observed. We were able to show for the first time that the darkening of a sample (measured in terms of transmission laser signal) is not necessarily caused by an increase of structural ordering in the sample. Possible transformations at lower temperatures could include a formation of non-graphitic light-absorbing intermediate organic carbon, a release of C−H groups or a decrease of carbonyl groups.

Interactive comment on "Investigation of structural changes of atmospheric aerosol samples during two thermal-optical measurement procedures (EUSAAR2, NIOSH870)" by Theresa Haller et al. Theresa Haller et al.