Formation of hydroxyl radicals from photolysis of secondary organic aerosol material
This paper demonstrates that OH radicals are formed by photolysis of secondary organic aerosol (SOA) material formed by terpene ozonolysis. The SOA is collected on filters, dissolved in water containing a radical trap (benzoic acid), and then exposed to ultraviolet light in a photochemical reactor....
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doaj-1cc785195bd64a3e8351706ffb647a8e2020-11-24T23:21:55ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242015-07-0115147831784010.5194/acp-15-7831-2015Formation of hydroxyl radicals from photolysis of secondary organic aerosol materialK. M. Badali0S. Zhou1D. Aljawhary2M. Antiñolo3W. J. Chen4A. Lok5E. Mungall6J. P. S. Wong7R. Zhao8J. P. D. Abbatt9University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaUniversity of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaUniversity of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaUniversity of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaUniversity of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaUniversity of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaUniversity of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaUniversity of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaUniversity of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaUniversity of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6, CanadaThis paper demonstrates that OH radicals are formed by photolysis of secondary organic aerosol (SOA) material formed by terpene ozonolysis. The SOA is collected on filters, dissolved in water containing a radical trap (benzoic acid), and then exposed to ultraviolet light in a photochemical reactor. The OH formation rates, which are similar for both α-pinene and limonene SOA, are measured from the formation rate of p-hydroxybenzoic acid as measured using offline HPLC analysis. To evaluate whether the OH is formed by photolysis of H<sub>2</sub>O<sub>2</sub> or organic hydroperoxides (ROOH), the peroxide content of the SOA was measured using the horseradish peroxidase-dichlorofluorescein (HRP-DCF) assay, which was calibrated using H<sub>2</sub>O<sub>2</sub>. The OH formation rates from SOA are 5 times faster than from the photolysis of H<sub>2</sub>O<sub>2</sub> solutions whose concentrations correspond to the peroxide content of the SOA solutions, assuming that the HRP-DCF signal arises from H<sub>2</sub>O<sub>2</sub> alone. The higher rates of OH formation from SOA are likely due to ROOH photolysis, but we cannot rule out a contribution from secondary processes as well. This result is substantiated by photolysis experiments conducted with t-butyl hydroperoxide and cumene hydroperoxide which produce over 3 times more OH than photolysis of equivalent concentrations of H<sub>2</sub>O<sub>2</sub>. Relative to the peroxide level in the SOA and assuming that the peroxides drive most of the ultraviolet absorption, the quantum yield for OH generation from α-pinene SOA is 0.8 ± 0.4. This is the first demonstration of an efficient photolytic source of OH in SOA, one that may affect both cloud water and aerosol chemistry.http://www.atmos-chem-phys.net/15/7831/2015/acp-15-7831-2015.pdf |
collection |
DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
K. M. Badali S. Zhou D. Aljawhary M. Antiñolo W. J. Chen A. Lok E. Mungall J. P. S. Wong R. Zhao J. P. D. Abbatt |
spellingShingle |
K. M. Badali S. Zhou D. Aljawhary M. Antiñolo W. J. Chen A. Lok E. Mungall J. P. S. Wong R. Zhao J. P. D. Abbatt Formation of hydroxyl radicals from photolysis of secondary organic aerosol material Atmospheric Chemistry and Physics |
author_facet |
K. M. Badali S. Zhou D. Aljawhary M. Antiñolo W. J. Chen A. Lok E. Mungall J. P. S. Wong R. Zhao J. P. D. Abbatt |
author_sort |
K. M. Badali |
title |
Formation of hydroxyl radicals from photolysis of secondary organic aerosol material |
title_short |
Formation of hydroxyl radicals from photolysis of secondary organic aerosol material |
title_full |
Formation of hydroxyl radicals from photolysis of secondary organic aerosol material |
title_fullStr |
Formation of hydroxyl radicals from photolysis of secondary organic aerosol material |
title_full_unstemmed |
Formation of hydroxyl radicals from photolysis of secondary organic aerosol material |
title_sort |
formation of hydroxyl radicals from photolysis of secondary organic aerosol material |
publisher |
Copernicus Publications |
series |
Atmospheric Chemistry and Physics |
issn |
1680-7316 1680-7324 |
publishDate |
2015-07-01 |
description |
This paper demonstrates that OH radicals are formed by photolysis of
secondary organic aerosol (SOA) material formed by terpene ozonolysis. The
SOA is collected on filters, dissolved in water containing a radical trap
(benzoic acid), and then exposed to ultraviolet light in a photochemical
reactor. The OH formation rates, which are similar for both α-pinene
and limonene SOA, are measured from the formation rate of p-hydroxybenzoic
acid as measured using offline HPLC analysis. To evaluate whether the OH is
formed by photolysis of H<sub>2</sub>O<sub>2</sub> or organic hydroperoxides (ROOH), the
peroxide content of the SOA was measured using the horseradish
peroxidase-dichlorofluorescein (HRP-DCF) assay, which was calibrated using
H<sub>2</sub>O<sub>2</sub>. The OH formation rates from SOA are 5 times faster than
from the photolysis of H<sub>2</sub>O<sub>2</sub> solutions whose concentrations
correspond to the peroxide content of the SOA solutions, assuming that the
HRP-DCF signal arises from H<sub>2</sub>O<sub>2</sub> alone. The higher rates of OH
formation from SOA are likely due to ROOH photolysis, but we cannot rule out
a contribution from secondary processes as well. This result is
substantiated by photolysis experiments conducted with t-butyl hydroperoxide
and cumene hydroperoxide which produce over 3 times more OH than
photolysis of equivalent concentrations of H<sub>2</sub>O<sub>2</sub>. Relative to the
peroxide level in the SOA and assuming that the peroxides drive most of the
ultraviolet absorption, the quantum yield for OH generation from α-pinene SOA is 0.8 ± 0.4. This is the first demonstration of an
efficient photolytic source of OH in SOA, one that may affect both
cloud water and aerosol chemistry. |
url |
http://www.atmos-chem-phys.net/15/7831/2015/acp-15-7831-2015.pdf |
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