Simulation of the diurnal variations of the oxygen isotope anomaly (Δ17O) of reactive atmospheric species
Atmospheric Chemistry and Physics Discussions
The isotope anomaly ( 17 O) of secondary atmospheric species such as nitrate (NO − 3 ) or hydrogen peroxide (H 2 O 2 ) has potential to provide useful constrains on their formation pathways. Indeed, the 17 O of their precursors (NO x , HO x etc.) differs and depends on their interactions with ozone, which is the main source of non-zero 17 O in the atmosphere. Interpreting variations of 17 O in secondary species requires an in-depth understanding of the 17 O of their precursors taking into
... s taking into account non-linear chemical regimes operating under various environmental settings. This article reviews and illustrates a series of basic concepts relevant to the propagation of the 17 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 x and HO x . Using a simplified but realistic tropospheric gas-phase chemistry mechanism, 17 O was propagated from ozone to other species (NO, NO 2 , OH, HO 2 , RO 2 , NO 3 , N 2 O 5 , HONO, HNO 3 , HNO 4 , H 2 O 2 ) according to the mass-balance equations, through the implementation of various sets of hypotheses pertaining to the transfer of 17 O during chemical reactions. The model results confirm that diurnal variations in 17 O of NO x predicted by the photochemical steady-state relationship during the day match those from the explicit treatment, but not at night. Indeed, the 17 O of NO x is "frozen" at night Correspondence to: S. Morin (firstname.lastname@example.org) as soon as the photolytical lifetime of NO x drops below ca. 10 min. We introduce and quantify the diurnally-integrated isotopic signature (DIIS) of sources of atmospheric nitrate and H 2 O 2 , which is of particular relevance to larger-scale simulations of 17 O where high computational costs cannot be afforded.