The nitrogen and oxygen stable isotopes (?15N & ?18O) of nitrogen oxides (NOx = nitric oxide (NO) + nitrogen dioxide (NO2)) may be a useful tool for partitioning NOx emission sources and for evaluating NOx photochemical cycling, but few measurements of in situ NOx exist. In this study, we have collected and characterized the diurnal variability in ?15N and ?18O of NO2 from ambient air at a small Midwestern city (West Lafayette, IN, USA, 40.426° N, 86.908° W) between July 7 to August 5, 2016, using an active sampling technique. Large variations were observed in both ?15N(NO2) and ?18O(NO2) that ranged from ?31.4 to 0.4‰ and 41.5–112.5‰, respectively.
April 6, 2018