Search

This study reports for the first-time the ambient concentrations of HULIS mass (HULIS-OM, Humic-like substances) and HULIS-C (carbon) in PM10 (particulate matter with aerodynamic diameter ≤ 10 μm) from the Indo-Gangetic Plain (IGP at Kanpur, wintertime). HULIS extraction followed by purification and isolation protocol with methanol: acetonitrile (1:1 v/v) on HLB (Hydrophilic-Lipophilic Balanced) cartridge has been established. Quantification of HULIS-C was achieved on a total organic carbon (TOC) analyser whereas HULIS-OM was determined gravimetrically. Consistently high recovery (> 90%) of HULIS-C based on analysis of Humic standard (sodium salt of Humic acid) suggested suitability of our established analytical protocol involving solvent extraction, purification and accurate quantification of HULIS. HULIS-OM varied from 17.3-38 μg m−3 during daytime and from 19.8-40.6 μg m−3 during night in this study. During daytime the HULIS-OM constituted 20-30% mass fraction of OMTotal and 10-15% of PM10 mass. However, a relatively low contribution of HULIS-OM has been observed during the night. This observation has been attributed to higher concentrations of OM and PM10 in night owing to nighttime chemical reactivity and condensation of organics in conjunction with shallower planetary boundary layer height. Strong correlation of HULIS-C with K+BB (R2 > 0.80) and significant day-night variability of HULIS-C/WSOC ratio in conjunction with air-mass back trajectories (showing transport of pollutants from upwind IGP) suggest biomass burning emission and secondary transformations as important sources of HULIS over IGP. High-loading of atmospheric PM10 (as high as 440 μg m−3) with significant contribution of water-soluble organic aerosols (WSOC/OC: ~ 0.40-0.80) during wintertime highlights their plausible potential role in fog and haze formation and their impact on regional-scale atmospheric radiative forcing over the IGP. [ABSTRACT FROM AUTHOR]

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]

Ion trap mass spectrometry (ITMS) was used to obtain further qualitative information about the chemical composition of humic-like substances (HULIS) in atmospheric particulate matter. Particles ≤10 μm (PM10) were collected on quartz fiber filters for 24 h in the region of Basel (Switzerland) and extracted with water. HULIS were separated from inorganic salts by size exclusion chromatography (SEC) and detected by electrospray ionization in the negative ion mode (ESI(−)). Series of consecutive fragment ion spectra (MSn) were recorded by ITMS. Full scan mass spectra of the extracts showed a mass distribution pattern characteristic for HULIS. Different molecular ions were selected from this pattern for further fragmentations. Among them the molecular ion m/ z 299 was considered as representative and intensively studied. Many MS2 and MS3 fragment spectra contained a fragment m/ z 97 and a neutral loss of 80 u. Time-of-flight (TOF) MS and deuterium exchange experiments identified m/ z 97 as hydrogen sulfate. MS2 and MS3 fragment spectra supported the existence of sulfate covalently bound to HULIS. The fragmentation behavior of sulfated HULIS could be confirmed by model compounds. [ABSTRACT FROM AUTHOR]

In this contribution we present to our knowledge the first investigations of macromolecular, often called humic-like substances (HULIS) in cloud water samples and compare them with water-soluble extracts from atmospheric PM2.5, soils and waters to study its possible origin. Chemical analysis was done using high performance liquid chromatography (HPLC) coupled with UV and diode array detector, and HPLC coupled with ESI-MS (electrospray ionization mass spectrometer). The data have been treated by principle component analysis (PCA) and cluster analysis to state similarities and/or differences between different types of samples. Our results show that the content of organic and inorganic species is distinctly different in smaller and larger droplets suggesting varying origin. We conclude that smaller droplets are formed more from organic containing condensation nuclei (CCN) and larger droplets more from inorganic containing CCN organic compounds. Putting all experimental findings together we state that HULIS in cloud water—and consequently in particulate CCN precursors—are produced in an atmospheric polymerization process from low molecular weighted organics of different origin. Evidence is found that anthropogenic sources contribute to this pathway. Cloud drops may act as reactor in this HULIS formation process but more likely are gas-phase or gas-to-particle interactions. [ABSTRACT FROM AUTHOR]