Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2016-1111
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
09 Jan 2017
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
Evidence for renoxification in the tropical marine boundary layer
Chris Reed1,a, Mathew J. Evans1,2, Leigh R. Crilley3, William J. Bloss3, Tomás Sherwen1, Katie A. Read1,2, James D. Lee1,2, and Lucy J. Carpenter1 1Wolfson Atmospheric Chemistry Laboratories (WACL), Department of Chemistry, University of York, Heslington, York, YO10 5DD, United Kingdom
2National Centre for Atmospheric Science (NCAS), University of York, Heslington, York, YO10 5DD, United Kingdom
3School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom
anow at: Facility for Airborne Atmospheric Measurements (FAAM), Building 146, Cranfield University, Cranfield, MK43 0AL, United Kingdom
Abstract. We present two years of NOx observations from the Cape Verde Atmospheric Observatory located in the tropical Atlantic boundary layer. We find NOx mixing ratios peak around solar noon (at 20–30 pptV depending on season), which is counter to box model simulations that show a midday minimum due to OH conversion of NO2 to HNO3. Production of NOx via decomposition of organic nitrogen species and the photolysis of HNO3 appear insufficient to provide the observed noon-time maximum. A rapid photolysis of nitrate aerosol to produce HONO and NO2, however, is able to simulate the observed diurnal cycle. This would make it the dominant source of NOx at this remote marine boundary layer site overturning the previous paradigm of transport of organic nitrogen species such as PAN being the dominant source. We show that observed mixing ratios (Nov–Dec 2015) of HONO at Cape Verde (~ 2.5 pptV peak at solar noon) are consistent with this route for NOx production. Reactions between the nitrate radical and halogen hydroxides which have been postulated in the literature appear to improve the box model simulation. This rapid conversion of aerosol phase nitrate to NOx changes our perspective of the NOx cycling chemistry in the tropical marine boundary layer, suggesting a more chemically complex environment than previously thought.

Citation: Reed, C., Evans, M. J., Crilley, L. R., Bloss, W. J., Sherwen, T., Read, K. A., Lee, J. D., and Carpenter, L. J.: Evidence for renoxification in the tropical marine boundary layer, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-1111, in review, 2017.
Chris Reed et al.
Chris Reed et al.

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Short summary
The source of ozone depleting compounds in the remote troposphere has been thought to be long range transport of secondary pollutants such as organic nitrates. Processing of organic nitrates to nitric acid and subsequent deposition on surfaces in the atmosphere was thought to remove these nitrates from the Ozone-NOx-HOx cycle. We found through observation of NOx in the remote tropical troposphere at the Cape Verde Observatory that surface nitrates can be released back into the atmosphere.
The source of ozone depleting compounds in the remote troposphere has been thought to be long...
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