Chemical properties of HULIS from three different environments

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.