Measurement report: Nitrogen isotopes ([delta].sup.15N) and first quantification of oxygen isotope anomalies (Î.sup.17O, [delta].sup.18O) in atmospheric nitrogen dioxide.

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From: Atmospheric Chemistry and Physics(Vol. 21, Issue 13)
Publisher: Copernicus GmbH
Document Type: Article
Length: 400 words

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Abstract :

The isotopic composition of nitrogen and oxygen in nitrogen dioxide (NO.sub.2) potentially carries a wealth of information about the dynamics of the nitrogen oxides (NO.sub.x = nitric oxide (NO) + NO.sub.2) chemistry in the atmosphere. While nitrogen isotopes of NO.sub.2 are subtle indicators of NO.sub.x emissions and chemistry, oxygen isotopes are believed to reflect only the O.sub.3 / NO.sub.x / VOC chemical regime in different atmospheric environments. In order to access this potential tracer of the tropospheric chemistry, we have developed an efficient active method to trap atmospheric NO.sub.2 on denuder tubes and measured, for the first time, its multi-isotopic composition ([delta].sup.15 N, [delta].sup.18 O, and Î.sup.17 O). The Î.sup.17 O values of NO.sub.2 trapped at our site in Grenoble, France, show a large diurnal cycle peaking in late morning at (39.2 ± 0.3) 0/00 and decreasing at night until (20.5 ± 0.3) 0/00. On top of this diurnal cycle, Î.sup.17 O also exhibits substantial daytime variability (from 29.7 0/00 to 39.2 0/00), certainly driven by changes in the O.sub.3 to peroxyl radicals (RO.sub.2) ratio. The nighttime decay of Î.sup.17 O(NO.sub.2) appears to be driven by NO.sub.2 slow removal, mostly from conversion into N.sub.2 O.sub.5, and its formation from the reaction between O.sub.3 and freshly emitted NO. As expected from a nighttime Î.sup.17 O(NO.sub.2) expression, our Î.sup.17 O(NO.sub.2) measured towards the end of the night is quantitatively consistent with typical values of Î.sup.17 O(O.sub.3). Daytime N isotope fractionation is estimated using a general expression linking it to Î.sup.17 O(NO.sub.2). An expression is also derived for the nighttime N isotope fractionation. In contrast to Î.sup.17 O(NO.sub.2 ), [delta].sup.15 N(NO.sub.2) measurements exhibit little diurnal variability (-11.8 0/00 to -4.9 0/00) with negligible isotope fractionations between NO and NO.sub.2, mainly due to high NO.sub.2 / NO.sub.x ratios, excepted during the morning rush hours. The main NO.sub.x emission sources are estimated using a Bayesian isotope mixing model, indicating the predominance of traffic emissions in this area. These preliminary results are very promising for using the combination of Î.sup.17 O and [delta].sup.15 N of NO.sub.2 as a probe of the NO.sub.x sources and fate and for interpreting nitrate isotopic composition records.

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Gale Document Number: GALE|A668379066