Abstract
Most pollutants in the Earth’s atmosphere are removed by oxidation with highly reactive hydroxyl radicals. Field measurements have revealed much higher concentrations of hydroxyl radicals than expected in regions with high loads of the biogenic volatile organic compound isoprene1,2,3,4,5,6,7,8. Different isoprene degradation mechanisms have been proposed to explain the high levels of hydroxyl radicals observed5,9,10,11. Whether one or more of these mechanisms actually operates in the natural environment, and the potential impact on climate and air quality, has remained uncertain12,13,14. Here, we present a complete set of measurements of hydroxyl and peroxy radicals collected during isoprene-oxidation experiments carried out in an atmospheric simulation chamber, under controlled atmospheric conditions. We detected significantly higher concentrations of hydroxyl radicals than expected based on model calculations, providing direct evidence for a strong hydroxyl radical enhancement due to the additional recycling of radicals in the presence of isoprene. Specifically, our findings are consistent with the unimolecular reactions of isoprene-derived peroxy radicals postulated by quantum chemical calculations9,10,11. Our experiments suggest that more than half of the hydroxyl radicals consumed in isoprene-rich regions, such as forests, are recycled by these unimolecular reactions with isoprene. Although such recycling is not sufficient to explain the high concentrations of hydroxyl radicals observed in the field, we conclude that it contributes significantly to the oxidizing capacity of the atmosphere in isoprene-rich regions.
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Acknowledgements
This work was supported by the EU FP-7 program EUROCHAMP-2 (grant agreement No. 228335) and by the EU FP-7 program PEGASOS (grant agreement No. 265307). S. Nehr and B. Bohn thank the Deutsche Forschungsgemeinschaft for financial support (grant agreement No. BO 1580/3-1). K. D. Lu thanks the National Natural Science Foundation of China (Major Program: 21190052) for financial support. The authors thank A. Buchholz, P. Schlag, F. Rubach, H-C. Wu, S. Dixneuf, M. Vietz, P. Müsgen and M. Bachner for additional measurements during this campaign and technical support.
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F.R., H.F. and B.B. designed experiments. H.F. performed model calculations for SAPHIR experiments. K.L. carried out model runs with updated isoprene chemistry for PRIDE-PRD2006. H.F. and A.H. wrote the manuscript. All authors contributed to the study with measurements, discussed results and commented on the manuscript.
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Fuchs, H., Hofzumahaus, A., Rohrer, F. et al. Experimental evidence for efficient hydroxyl radical regeneration in isoprene oxidation. Nature Geosci 6, 1023–1026 (2013). https://doi.org/10.1038/ngeo1964
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DOI: https://doi.org/10.1038/ngeo1964
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