Search

Humic-like substances (HULIS) comprise a significant fraction of the organic compounds in aerosol particles. In the present study we report the chemical properties of HULIS samples originating from urban (Copenhagen, Denmark), rural (Melpitz, Germany) and remote (Storm Peak Laboratory, CO, USA) environments. Suwannee River Fulvic Acid Standard (SRFA) was included in the study as a reference. Raman, Fourier transform infrared (FTIR) and ultraviolet-visible (UV-Vis) spectroscopy were used together with high performance liquid chromatography-mass spectrometry (HPLC-MS) for characterisation of the samples. The same main functional groups were present in all samples, but the relative abundance of functional groups varied among the studied samples, which was mainly evident from the FTIR spectra. The urban and rural samples were found to be very similar with respect to the relative abundance of functional groups. The remote sample contained relatively more C=O and COOH groups, which may be due to the remote environment. Organonitrates appeared to be present in the three atmospheric samples, while it did not appear to be present in the SRFA. The SRFA sample comprised significantly larger amounts of aromatic groups relative to the atmospheric samples in line with previous findings. All the obtained mass spectra showed clear periods of 14-16 Da in line with previous studies. The estimated average molecular weight (AMW) was comparable for the atmospheric samples within the errors - while the AMW of SRFA was higher. In general the atmospheric HULIS samples from different environments were rather similar with respect to the properties investigated. [ABSTRACT FROM AUTHOR]

This work focuses on presenting a new methodology, based on approach-retraction curves, to objectively and accurately measure adhesion and tackiness of industrial greases. The definitions of pull-off force and tackiness are redefined, explained and measured, whereas the effect of testing parameters such as retraction speed, grease film thickness, applied load and temperature is discussed. This work aims to point out that the adhesion and tackiness of greases are not just a single value, but that they strongly depend on the experimental conditions. Based on this proposed method, a mapping of the tackiness of greases with respect to the experimental or working conditions can be performed. [ABSTRACT FROM AUTHOR]