Diurnal variations in oxygen and nitrogen isotopes of atmospheric nitrogen dioxide and nitrate: implications for tracing NO_x oxidation pathways and emission sources

International audienceThe oxygen (∆17O) and nitrogen (∂15) isotopic compositions of atmospheric nitrate (NO3−) are widely used as tracers of its formation pathways, precursor (nitrogen oxides NOx = nitric oxide NO + nitrogen NO2) emission sources, and physico-chemical processing. However, the critical lack of observations on the multi-isotopic composition of NO2 maintainssignificant uncertainties regarding the links between the isotopic composition of NOx and NO3−, which may bias estimates ofthe NO3− formation processes and the distribution of sources. We report here on the first simultaneous atmospheric observations of ∆17O and ∂15 in NO2 and NO3−