Dependence between the photochemical age of light aromatic hydrocarbons and the carbon isotope ratios of atmospheric nitrophenols
<p>Concepts were developed to establish relationships between the stable carbon isotope ratios of nitrophenols in the atmosphere and the photochemical processing of their precursors, light aromatic volatile organic compounds. These concepts were based on the assumption that nitrophenols are fo...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/5495/2019/acp-19-5495-2019.pdf |
| Summary: | <p>Concepts were developed to establish relationships between the stable carbon
isotope ratios of nitrophenols in the atmosphere and the photochemical processing
of their precursors, light aromatic volatile organic compounds. These concepts
were based on the assumption that nitrophenols are formed dominantly from the
photo-oxidation of aromatic volatile organic compounds (VOCs). A mass balance model as well as various
scenarios based on the proposed mechanism of nitrophenol formation were
formulated and applied to derive the time-integrated exposure of the
precursors to processing by OH radicals (<span class="inline-formula">∫</span>[OH]d<span class="inline-formula"><i>t</i></span>) from ambient
observations made between 2009 and 2012 in Toronto, Canada. The mechanistic
model included the possibility of isotopic fractionation during intermediate
steps, rather than only during the initial reaction step. This model takes
kinetic isotope effects for the reaction of the precursor VOC with
the hydroxyl radical and their respective rate constants into account, as well as carbon
isotope ratio source signatures. While many of these values are known, there
are some, such as the kinetic isotope effects of reactions of first- and
second-generation products, which are unknown. These values were predicted in
this study based on basic principles and published laboratory measurements of kinetic
carbon isotope effects and were applied to the mechanistic model. Due to the
uncertainty of the estimates based on general principles, three scenarios were
used with different values for isotope effects that were not known from
laboratory studies. Comparison of the dependence between nitrophenol carbon
isotope ratios and <span class="inline-formula">∫</span>[OH]d<span class="inline-formula"><i>t</i></span> with published results of laboratory
studies and ambient observations was used to narrow the range of plausible
scenarios for the mechanistic model. The results also suggests that mass-balance-based
models do not adequately describe the dependence between
nitrophenol carbon isotope ratios and <span class="inline-formula">∫</span>[OH]d<span class="inline-formula"><i>t</i></span>.</p> |
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| ISSN: | 1680-7316 1680-7324 |