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

Abstract. The reactivity of NO3 plays an important role in modifying the fate reactive nitrogen species at nighttime. High (e.g. towards unsaturated volatile organic compounds – VOCs) can lead to formation nitrates and secondary aerosol, whereas low opens possibility heterogeneous NOx losses via uptake N2O5 particles. We present direct measurements (kNO3) that quantify VOC-induced during TO2021 campaign summit Kleiner Feldberg mountain (825 m, Germany) July 2021. kNO3 was on average ?0.035 s?1 daytime, ?0.015 for almost half nights below detection limit 0.006 other half, which may be linked sampling from above nocturnal surface layer. reactivities derived VOC corresponding rate coefficient were good agreement with kNO3, monoterpenes representing 84 % total reactivity. fractional contribution F overall loss (which includes additional reaction NO photolysis) ?16 daytime ?50 %–60 relatively nighttime value is related presence several tens parts per trillion by volume (pptv) nights. mixing ratios not measured, but steady-state calculations resulted values between <1 12 pptv. A comparison results previous campaigns 2008 2015 this site revealed rates remarkably high TO2021, while production low. observed up 80 pptv night, has implications cycling site. With O3 levels mostly 25 60 ppbv (parts billion volume), oxidized NO2 a timescale few minutes. find maintaining of, e.g., 40 requires ground-level emission 0.33 (into shallow layer 10 m depth). This turn rapid deposition (vdNO2?0.15 cm s?1) reduce match observations.