Preprints
https://doi.org/10.5194/acp-2022-163
https://doi.org/10.5194/acp-2022-163
 
07 Mar 2022
07 Mar 2022
Status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

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

Patrick Dewald, Clara M. Nussbaumer, Jan Schuladen, Akima Ringsdorf, Achim Edtbauer, Horst Fischer, Jonathan Williams, Jos Lelieveld, and John N. Crowley Patrick Dewald et al.
  • Atmospheric Chemistry Department, Max Planck Institut für Chemie, 55128 Mainz, Germany

Abstract. The reactivity of NO3 plays an important role in modifying the fate of reactive nitrogen species at nighttime. High reactivity (e.g. towards unsaturated VOCs) can lead to formation of organic nitrates and secondary organic aerosol, whereas low reactivity opens the possibility of heterogeneous NOX losses via formation and uptake of N2O5 to particles.

We present direct NO3 reactivity measurements (kNO3) that quantify the VOC-induced losses of NO3 during the TO2021 campaign at the summit of the Kleiner Feldberg mountain (825 m, Germany) in July 2021. kNO3 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. NO3 reactivities derived from VOC measurements and the corresponding rate coefficient were in good agreement with kNO3, with monoterpenes representing 84 % of the total reactivity. The fractional contribution F of kNO3 to the overall NO3 loss rate (which includes additional reaction of NO3 with NO and photolysis) were on average ~16 % during the daytime and ~50–60 % during the nighttime. The relatively low nighttime value of F is related to the presence of several tens of pptv of NO on several nights. NO3 mixing ratios were not measured but steady-state calculations resulted in nighttime values between < 1 pptv and 12 pptv. A comparison of results from TO2021 with direct measurements of NO3 during previous campaigns between 2008 and 2015 at this site revealed that NO3 loss rates were remarkably high during TO2021, while NO3 production rates were low.

We observed NO mixing ratios of up to 80 pptv at night which has implications for the cycling of reactive nitrogen at this site. With O3 present at levels of mostly 25 to 60 ppbv, NO is oxidised to NO2 on a time-scale of a few minutes. We find that to maintain NO mixing ratios of e.g. 40 pptv requires a ground-level NO emission rate of 0.33 pptv s-1 (into a shallow surface layer of 10 m depth). This in turn requires rapid deposition of NO2 to the surface (vdNO2 ~ 0.15 cm s-1) to reduce nocturnal NO2 levels to match the observations.

Patrick Dewald et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-163', Anonymous Referee #1, 23 Mar 2022
  • RC2: 'Comment on acp-2022-163', Anonymous Referee #2, 15 Apr 2022

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-163', Anonymous Referee #1, 23 Mar 2022
  • RC2: 'Comment on acp-2022-163', Anonymous Referee #2, 15 Apr 2022

Patrick Dewald et al.

Patrick Dewald et al.

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Short summary
We measured the gas-phase reactivity of the NO3 radical on the summit (825 m a.s.l.) of a semi-rural mountain in south-west Germany in July 2021. The impact of VOC-induced NO3 losses (mostly monoterpenes) in competition to loss by reaction with NO and photolysis throughout the diel cycle was estimated. Beside chemistry, boundary layer dynamics and plant-physiological processes presumably have a great impact on our observations, which were compared to previous NO3 measurements on the same site.
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