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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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  08 Dec 2020

08 Dec 2020

Review status: this preprint is currently under review for the journal AMT.

Long-term NOx measurements in the remote marine tropical troposphere

Simone T. Andersen1, Lucy J. Carpenter1, Beth S. Nelson1, Luis Neves2, Katie A. Read1,3, Chris Reed4, Martyn Ward1, Matthew J. Rowlinson1,3, and James D. Lee1,3 Simone T. Andersen et al.
  • 1Wolfson Atmospheric Chemistry Laboratories (WACL), Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK
  • 2Instituto Nacional de Meteorologia e Geofísica, São Vicente (INMG), Mindelo, Cabo Verde
  • 3National Centre for Atmospheric Science (NCAS), University of York, Heslington, York, YO10 5DD, UK
  • 4FAAM Airborne Laboratory, Building 146, Cranfield University, Cranfield, MK43 0AL, UK

Abstract. Atmospheric nitrogen oxides (NO + NO2 = NOx) have been measured at the Cape Verde Atmospheric Observatory (CVAO) in the tropical Atlantic (16° 51' N, 24° 52' W) since October 2006. These measurements represent a unique time series of NOx in the background remote troposphere. Nitrogen dioxide (NO2) is measured via photolytic conversion to nitric oxide (NO) by ultra violet light emitting diode arrays followed by chemiluminescence detection. Since the measurements began, a blue light converter (BLC) has been used for NO2 photolysis, with a maximum spectral output of 395 nm from 2006–2015 and of 385 nm from 2015. The original BLC used was constructed with a Teflon-like material and appeared to cause an overestimation of NO2 when illuminated. To avoid such interferences, a new additional photolytic converter (PLC) with a quartz photolysis cell (maximum spectral output also 385 nm) was implemented in March 2017. Once corrections are made for the NO2 artefact from the original BLC, the two NO2 converters are shown to give comparable NO2 mixing ratios (PLC = 0.92 × BLC, R2 = 0.92), giving confidence in the quantitative measurement of NOx at very low levels. Data analysis methods for the NOx measurements made at CVAO have been developed and applied to the entire time series to produce an internally consistent and high quality long-term data set. NO has a clear diurnal pattern with a maximum mixing ratio of 2–10 pptV during the day depending on the season and ~0 pptV during the night. NO2 shows a fairly flat diurnal signal, although a small increase in daytime NOx is evident in some months. Monthly average mixing ratios of NO2 vary between 5 and 30 pptV depending on the season. Clear seasonal trends in NO and NO2 levels can be observed with a maximum in autumn/winter and a minimum in spring/summer.

Simone T. Andersen et al.

Status: open (until 02 Feb 2021)
Status: open (until 02 Feb 2021)
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Simone T. Andersen et al.

Simone T. Andersen et al.


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