Fate of the nitrate radical at the summit of a semi-rural mountain site in Germany assessed with direct reactivity measurements

The reactivity of NO 3 plays an important role in modifying the fate of reactive nitrogen species at nighttime. High reactivity (e.g. towards unsaturated volatile organic compounds – VOCs) can lead to formation of organic nitrates and secondary organic aerosol, whereas low reactivity opens the possibility of heterogeneous NO x losses via the formation and uptake of N 2 O 5 to particles. We present direct NO 3 reactivity measurements ( k NO 3 ) that quantify the VOC-induced losses of NO 3 during the TO2021 campaign at the summit of the Kleiner Feldberg mountain (825 m, Germany) in July 2021. k NO 3 was on average ∼0.035 s −1 during the daytime, ∼0.015 s −1 for almost half of the nights and below the detection limit of 0.006 s −1 for the other half, which may be linked to sampling from above the nocturnal surface layer. NO 3 reactivities derived from VOC measurements and the corresponding rate coefficient were in good agreement with k NO 3 , with monoterpenes representing 84 % of the total ...