Evidence of a biogenic source of oxalic acid in marine aerosol

MARIA CRISTINA FACCHINI (1) , Matteo Rinaldi (1) , Darius Ceburnis (2) , Colin D. O’Dowd (2) , Jean . Sciare (3), John P. Burrows (4)

(1) Institute of Atmospheric Sciences and Climate (ISAC-CNR), Italy (2) Department of Experimental Physics & Environmental Change Institute, National University of Ireland Galway, University Road, Galway, Ireland (3) Laboratoire des Sciences du Climat et de l’Environnement, CNRS-CEA-IPSL, Gif-sur-Yvette, France. (4) Institute of Environmental Physics and Remote Sensing, IUP, University of Bremen, Germany.

     Abstract Number: 109
     Last modified: April 7, 2010

Abstract
We present results suggesting the existence of a biogenic source of oxalic acid over the oceans. Oxalic acid has been often observed in marine aerosol, nevertheless, given the ubiquitous character and the high concentrations found in polluted environments, its origin has always been attributed mainly to continental sources.
In this work oxalic acid is detected clean marine aerosol samples at Mace Head (53°20’N, 9°54’W) in concentrations ranging from 2.7 to 39 ng m-3 and at Amsterdam Island (37°48’S, 77°34’E) in concentration ranging from 0.31 to 17 ng m-3. In both hemispheres, oxalic acid concentration show a clear seasonal trend, with maxima in spring-summer and minima in the fall-winter period, in analogy with other marine biogenic aerosol components (e.g., MSA).
Oxalic acid mass size distribution presents a peak in the 1-2.5 µm size range in both the sites while in continentally influenced samples collected at Mace Head, a mode in the submicron rage is observed . Although this can be explained by the different partitioning of oxalic acid due to the different acid-base properties of marine and polluted aerosol, it can also suggest the existence of a peculiar oxalic acid oceanic source. The most likely oxalic acid formation pathways in the marine boundary layer are in fact the photochemical oxidation of biogenic unsaturated fatty acids and in-cloud oxidation of glyoxal. We also present satellite observations of glyoxal over the two marine regions, showing a seasonal trend similar to that of aerosol oxalic acid.