Simulation of the diurnal variations of the oxygen isotope anomaly (Δ<sup>17</sup>O) of reactive atmospheric species
The isotope anomaly (Δ<sup>17</sup>O) of secondary atmospheric species such as nitrate (NO<sub>3</sub><sup>−</sup>) or hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) has potential to provide useful constrains on their...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2011-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/11/3653/2011/acp-11-3653-2011.pdf |
| Summary: | The isotope anomaly (Δ<sup>17</sup>O) of secondary atmospheric species such as nitrate (NO<sub>3</sub><sup>−</sup>) or hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) has potential to provide useful constrains on their formation pathways. Indeed, the Δ<sup>17</sup>O of their precursors (NO<sub>x</sub>, HO<sub>x</sub> etc.) differs and depends on their interactions with ozone, which is the main source of non-zero Δ<sup>17</sup>O in the atmosphere. Interpreting variations of Δ<sup>17</sup>O in secondary species requires an in-depth understanding of the Δ<sup>17</sup>O of their precursors taking into account non-linear chemical regimes operating under various environmental settings. <br><br> This article reviews and illustrates a series of basic concepts relevant to the propagation of the Δ<sup>17</sup>O of ozone to other reactive or secondary atmospheric species within a photochemical box model. We present results from numerical simulations carried out using the atmospheric chemistry box model CAABA/MECCA to explicitly compute the diurnal variations of the isotope anomaly of short-lived species such as NO<sub>x</sub> and HO<sub>x</sub>. Using a simplified but realistic tropospheric gas-phase chemistry mechanism, Δ<sup>17</sup>O was propagated from ozone to other species (NO, NO<sub>2</sub>, OH, HO<sub>2</sub>, RO<sub>2</sub>, NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub>, HONO, HNO<sub>3</sub>, HNO<sub>4</sub>, H<sub>2</sub>O<sub>2</sub>) according to the mass-balance equations, through the implementation of various sets of hypotheses pertaining to the transfer of Δ<sup>17</sup>O during chemical reactions. <br><br> The model results confirm that diurnal variations in Δ<sup>17</sup>O of NO<sub>x</sub> predicted by the photochemical steady-state relationship during the day match those from the explicit treatment, but not at night. Indeed, the Δ<sup>17</sup>O of NO<sub>x</sub> is "frozen" at night as soon as the photolytical lifetime of NO<sub>x</sub> drops below ca. 10 min. We introduce and quantify the diurnally-integrated isotopic signature (DIIS) of sources of atmospheric nitrate and H<sub>2</sub>O<sub>2</sub>, which is of particular relevance to larger-scale simulations of Δ<sup>17</sup>O where high computational costs cannot be afforded. |
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| ISSN: | 1680-7316 1680-7324 |