Coastal iodine emissions: part 2. Chamber experiments of particle formation from Laminaria digitata-derived and laboratory-generated I2
Monahan, Ciaran; Ashu-Ayem, Enowmbi R.; Nitschke, Udo; Darby, Steven B.; Smith, Paul D.; Stengel, Dagmar B.; Venables, Dean S.; O'Dowd, Colin D.
Date:
2012
Copyright:
Copyright © 2012 American Chemical Society. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Environmental Science and Technology, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/es3011805
Citation:
MONAHAN, C., ASHU-AYEM, E. R., NITSCHKE, U., DARBY, S. B., SMITH, P. D., STENGEL, D. B., VENABLES, D. S. & O’DOWD, C. D. 2012. Coastal Iodine Emissions: Part 2. Chamber Experiments of Particle Formation from Laminaria digitata-Derived and Laboratory-Generated I2. Environmental Science & Technology, 46, 10422-10428. doi: 10.1021/es3011805
Abstract:
Laboratory studies into particle formation from Laminaria digitata macroalgae were undertaken to elucidate aerosol formation for a range of I2 (0.3−76 ppbv) and O3(<3−96 ppbv) mixing ratios and light levels (EPAR = 15, 100,and 235 μmol photons m−2 s−1). No clear pattern was observed for I2 or aerosol parameters as a function of light levels. Aerosol mass fluxes and particle number concentrations,were, however, correlated with I2 mixing ratios for low O3mixing ratios of <3 ppbv (R2 = 0.7 and 0.83, respectively for low light levels, and R2 = 0.95 and 0.98, respectively for medium lightlevels). Additional experiments into particle production as a function of laboratory-generated I2, over a mixing ratio range of 1−8ppbv, were conducted under moderate O3 mixing ratios (∼24 ppbv) where a clear, 100-fold or greater, increase in the aeroso lnumber concentrations and mass fluxes was observed compared to the low O3 experiments. A linear relationship between particle concentration and I2 was found, in reasonable agreement with previous studies. Scaling the laboratory relationship to aerosol concentrations typical of the coastal boundary layer suggests a I2 mixing ratio range of 6−93 pptv can account for the observed particle production events. Aerosol number concentration produced from I2 is more than a factor of 10 higher than thatproduced from CH2I2 for the same mixing ratios.
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