Abstract
Abstract. Humic-Like Substances (HULIS) are a major contributor to the organic carbon in atmospheric aerosol. It would be necessary to standardize an analytical method that could be easily and routinely used for HULIS measurements. We present one of the first comparisons of two of the main methods in use to extract HULIS, using I) a weak anion exchanger (DEAE) and II) the combination of two separation steps, one according to polarity (on C18) and the second according to acidity (with a strong anion exchanger SAX). The quantification is performed with a TOC analyzer, complemented by an investigation of the chemical structure of the extracted fractions by UV-Visible spectroscopy. The analytical performances of each method are determined and compared for humic substances standards. These methods are further applied to determine the water extractable HULIS (HULISWS) and the 0.1 M NaOH alkaline extractable HULIS (HULIS T) in atmospheric aerosol collected in an Alpine Valley during winter time. This comparison, although on a limited batch of samples shows that the simpler DEAE isolation procedure leads to higher recoveries and better reproducibility than the C18-SAX procedure, and might therefore be preferable.
Highlights
In order to determine the respective performances of the DEAE and C18-SAX methods, different analytical characteristics such as linear range, reproducibility and extraction yield were studied with SRFA standard solutions
We can conclude that a higher uncertainty can result when correcting the Humic Like Substances (HULIS) concentrations measured in actual atmospheric samples for the extraction yield as determined with SRFA for the C18+SAX method
HULIS are a major contributor to the organic carbon fraction in atmospheric aerosol
Summary
The organic fraction represents an important part of atmospheric aerosols, both from a mass point of view with up to 50% in total mass (Putaud et al, 2004; Pio et al, 2007) and because it can largely influence physical and chemical properties of particles. It was recently shown that macromolecular species are important contributors to the unresolved mass of POM, comprising between 10–30% by mass in marine, rural and tropospheric aerosol (Feczko et al, 2007). This significant fraction is commonly referred to as HULIS (HUmic LIke Substances), because of its physical and chemical similarities with terrestrial and aquatic humic and fulvic acids (Graber and Rudich, 2006, and references therein). By definition HULIST can be directly extracted with 0.1 M NaOH
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