ATMOCHEM - Secondary organic aerosol production in the lower free troposphere over western Europe
Final Report Abstract
The climate forcing potential of aerosols is only loosely known, thus limiting the capability of models in simulating future climate changes. This is particulate true in view of the atmospheric load of organic carbon particles where the present dominating sources are not well quantified and besides the fact that their long term change is virtually unknown. In a collaborative effort with the Laboratoire de Glaciologie et Géophysique de l’Environnement (CRNS/ Grenoble) this lack of knowledge could be significantly reduced by combining two innovative attempts: (1) making use of adequate Alpine ice cores for reconstructing high resolution records of the water soluble organic ice content back to 1920 (including associated species of various organic acids) and, (2) deploying first micro-radiocarbon analysis to obtain a quantitative estimate of the fossil versus the biogenic fraction of the dissolved organic carbon. Major results of this endeavour comprise the first, seasonally resolved and quasi-continuous record of dissolved carbon covering the important part of the industrialization era. While an overall increase over that period by a factor three in summer and a factor of two in winter concentrations is seen, only up to 60% of this dissolved total organic carbon can be explained by concurrently analyzed organic species. The radiocarbon signature of dissolved organic carbon specifically analyzed in ice core samples over the thermonuclear bomb test period revealed, however, that: (i) only about one quarter of this dissolved organic carbon comes from fossil sources (with little temporal change of this partitioning), and (ii) that most of the non-fossil fraction is evidently produced by the contemporary living biosphere. Combined, these findings imply that the significant long term increase in the atmospheric load of (secondary) organic aerosol is driven by changes related to biogenic emission and their conversion rate to secondary aerosols. Thus, direct man made emission of organic material to the atmosphere appears to have been not decisive for the significant increase in the organic aerosol load over Europe. Overall, this is an surprising result, keeping in mind that the long term increase of the organic carbon in ice cores broadly goes along with the anthropogenic enhancement of inorganic aerosol components like sulphate and nitrate being closely associated with fossil fuel combustion.
Publications
- (2009), Radiocarbon micro-analysis on ice impurities for dating of Alpine glaciers, PhD Thesis, Institut für Umweltphysik, Heidelberg University, Germany
May, B.
- 2011. Quantification of Dissolved Organic Carbon at Very Low Levels in Natural Ice Samples by a UV- Induced Oxidation Method. Environ. Sci. Technol., 45(2), 673–678
Preunkert, S. Legrand M, Stricker P, Bulat S, Alekhina I, Petit JR, Hoffmann H, May B, Jourdain B.
- Constraints on the major sources of dissolved organic carbon in Alpine ice cores from Radiocarbon analysis over the bomb peak period, J. Geophys. Res., vol. 118, 1–9
May, B., D. Wagenbach, H. Hoffmann, M. Legrand, S. Preunkert, and P. Steier
(See online at https://doi.org/10.1002/jgrd.50200) - Major 20th century changes of the content and chemical speciation of organic carbon archived in Alpine ice cores: implications for the long-term change of organic aerosol over Europe, J. Geophys. Res., 2013
Legrand, M., S. Preunkert, B. May, J. Guilhermet, H. Hoffmann, and D. Wagenbach
(See online at https://doi.org/10.1002/jgrd.50202)
