Abstract. The isotopic composition of nitrogen and oxygen in nitrogen
dioxide (NO2) potentially carries a wealth of information about the
dynamics of the nitrogen oxides (NOx = nitric oxide (NO) + NO2) chemistry in the atmosphere. While nitrogen isotopes of NO2
are subtle indicators of NOx emissions and chemistry, oxygen isotopes
are believed to reflect only the O3 / NOx / 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 NO2 on denuder tubes and measured, for the first
time, its multi-isotopic composition (δ15N, δ18O,
and Δ17O). The Δ17O values of NO2 trapped at
our site in Grenoble, France, show a large diurnal cycle peaking in late
morning at (39.2 ± 0.3) ‰ and decreasing at night
until (20.5 ± 0.3) ‰. On top of this diurnal
cycle, Δ17O also exhibits substantial daytime variability (from
29.7 ‰ to 39.2 ‰), certainly driven by changes in the
O3 to peroxyl radicals (RO2) ratio. The nighttime decay of
Δ17O(NO2) appears to be driven by NO2 slow removal,
mostly from conversion into N2O5, and its formation from the
reaction between O3 and freshly emitted NO. As expected from a
nighttime Δ17O(NO2) expression, our Δ17O(NO2) measured towards the end of the night is quantitatively
consistent with typical values of Δ17O(O3). Daytime N
isotope fractionation is estimated using a general expression linking it to
Δ17O(NO2). An expression is also derived for the nighttime
N isotope fractionation. In contrast to Δ17O(NO2),
δ15N(NO2) measurements exhibit little diurnal variability
(−11.8 ‰ to −4.9 ‰) with negligible isotope fractionations between NO and NO2, mainly due to high
NO2 / NOx ratios, excepted during the morning rush hours. The main
NOx 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
Δ17O and δ15N of NO2 as a probe of the
NOx sources and fate and for interpreting nitrate isotopic composition
records.