Determination of water and alkaline extractable atmospheric humic-like substances with the TU Vienna HULIS analyzer in samples from six background sites in Europe

[1] With a newly developed method based on the combination of two separation steps (by polarity and by acidity) with a universal detector for organic carbon, efficient isolation of humic-like substances (HULIS) from the matrix and quantitative determination of the isolated organic carbon is achieved. This new method was applied to determine the water extractable (HULISWS) and, in sequence, the 0.1 M NaOH alkaline extractable HULIS (HULISAS) fractions in aerosol from six sites situated at a transect from west to east across Europe. The sum of the two HULIS fractions is here defined as total HULIS (HULIST). The lowest 12-month average concentrations of HULIST ranged from 0.075 mgC/m the Azores (Portugal) to 1.7 mgC/m at the continental background site K-puszta (Hungary). On the continent, the HULIST concentration decreases exponentially with elevation. The relative amounts of water extractable and alkaline soluble HULIS were relatively similar at the six sites. Dramatic differences were observed for the seasonal variations of the HULIS fractions at the different sites. At the Azores, as well as at the higher mountain sites (1450 and 3100 m), a summer maximum of the HULIST concentration was observed, while at the continental low-level sites (Aveiro and K-puszta), winter maxima dominated the seasonal variation. The summer/winter ratio of the HULIST concentration varied from 7.1 at Sonnblick to 0.36 at Aveiro. The seasonal variation at the two continental lower-level sites with winter maxima might be explained by overlapping of a weaker summer source and a stronger winter source.