Methodological insights for accurate quantification of trace elements in soluble and insoluble fractions of bulk atmospheric deposition

This study explores the distribution of 16 trace elements between soluble and insoluble fractions of atmospheric deposition in Sicily, Italy, based on EU protocols for monitoring pollutants. Using a standardised deposimeter, we collected 149 atmospheric deposition samples over two years. Additionally, we analysed the rinse solution of the deposimeter separately. Higher deposition values for elements like Sr, B, Ba, Zn, As, and Cu were found in the soluble fraction, whereas Fe, Ti, Al, Cr, Co, Li, Mn, V, Ni, and Pb were prevalent in the insoluble fraction. The rinse fraction typically accounted for lower deposition values (from 1 % to 19 %), except for Pb and B, which accounted for 42 % and 31 % of the total deposition. We compared trace element distribution during a "dry period" and a "wet period." During the dry period, the insoluble fraction represented up to 97 % for elements like Ti and Fe, while the rinse fraction was notable for B (∼51 %) and Pb (∼33 %). In the wet period, insoluble contributions were higher for Li, Al, Ti, Cr, Fe, Co, and Pb, and soluble contributions increased for B, V, Mn, Zn, As, Sr, Ba, and Cu. While soluble elements were affected by temporal precipitation distribution, less soluble elements like Ti, Fe, and Al showed no significant differences between periods. Overall, the study highlights varying degrees of solubility among trace elements. Although the rinse fraction was generally negligible for most elements, overlooking it could lead to underestimating total atmospheric deposition for some elements, especially after extended dry periods.