Heterogeneous photochemistry of imidazole-2-carboxaldehyde: HO<sub>2</sub> radical
formation and aerosol growth
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Published:2016-09-23
Issue:18
Volume:16
Page:11823-11836
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
González Palacios Laura, Corral Arroyo Pablo, Aregahegn Kifle Z., Steimer Sarah S.ORCID, Bartels-Rausch ThorstenORCID, Nozière BarbaraORCID, George ChristianORCID, Ammann MarkusORCID, Volkamer RainerORCID
Abstract
Abstract. The multiphase chemistry of glyoxal is a source of secondary organic aerosol (SOA), including its light-absorbing product imidazole-2-carboxaldehyde (IC). IC is a photosensitizer that can contribute to additional aerosol ageing and growth when its excited triplet state oxidizes hydrocarbons (reactive uptake) via H-transfer chemistry. We have conducted a series of photochemical coated-wall flow tube (CWFT) experiments using films of IC and citric acid (CA), an organic proxy and H donor in the condensed phase. The formation rate of gas-phase HO2 radicals (PHO2) was measured indirectly by converting gas-phase NO into NO2. We report on experiments that relied on measurements of NO2 formation, NO loss and HONO formation. PHO2 was found to be a linear function of (1) the [IC] × [CA] concentration product and (2) the photon actinic flux. Additionally, (3) a more complex function of relative humidity (25 % < RH < 63 %) and of (4) the O2 ∕ N2 ratio (15 % < O2 ∕ N2 < 56 %) was observed, most likely indicating competing effects of dilution, HO2 mobility and losses in the film. The maximum PHO2 was observed at 25–55 % RH and at ambient O2 ∕ N2. The HO2 radicals form in the condensed phase when excited IC triplet states are reduced by H transfer from a donor, CA in our system, and subsequently react with O2 to regenerate IC, leading to a catalytic cycle. OH does not appear to be formed as a primary product but is produced from the reaction of NO with HO2 in the gas phase. Further, seed aerosols containing IC and ammonium sulfate were exposed to gas-phase limonene and NOx in aerosol flow tube experiments, confirming significant PHO2 from aerosol surfaces. Our results indicate a potentially relevant contribution of triplet state photochemistry for gas-phase HO2 production, aerosol growth and ageing in the atmosphere.
Funder
European Commission Division of Atmospheric and Geospace Sciences
Publisher
Copernicus GmbH
Subject
Atmospheric Science
Reference57 articles.
1. Aregahegn, K. Z., Nozière, B., and George, C.: Organic aerosol formation photo-enhanced by the formation of secondary photosensitizers in aerosols, Faraday Discuss., 165, 123–134, https://doi.org/10.1039/C3FD00044C, 2013. 2. Atkinson, R., Baulch, D. L., Cox, R. A., Crowley, J. N., Hampson, R. F., Hynes, R. G., Jenkin, M. E., Rossi, M. J., and Troe, J.: Evaluated kinetic and photochemical data for atmospheric chemistry: Volume I – gas phase reactions of Ox, HOx, NOx and SOx species, Atmos. Chem. Phys., 4, 1461–1738, https://doi.org/10.5194/acp-4-1461-2004, 2004. 3. Badali, K. M., Zhou, S., Aljawhary, D., Antiñolo, M., Chen, W. J., Lok, A., Mungall, E., Wong, J. P. S., Zhao, R., and Abbatt, J. P. D.: Formation of hydroxyl radicals from photolysis of secondary organic aerosol material, Atmos. Chem. Phys., 15, 7831–7840, https://doi.org/10.5194/acp-15-7831-2015, 2015. 4. Calvert, J. G. and Pitts, J. N.: Photochemistry, Wiley, New York, 1966. 5. Canonica, S., Jans, U., Stemmler, K., and Hoigne, J.: Transformation Kinetics of Phenols in Water: Photosensitization by Dissolved Natural Organic Material and Aromatic Ketones, Environ. Sci. Technol., 29, 1822–1831, https://doi.org/10.1021/es00007a020, 1995.
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