Evidence for renoxification in the tropical marine boundary layer
We present 2 years of NO<sub><i>x</i></sub> observations from the Cape Verde Atmospheric Observatory located in the tropical Atlantic boundary layer. We find that NO<sub><i>x</i></sub> mixing ratios peak around solar noon (at 20–30 pptV depending on se...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/4081/2017/acp-17-4081-2017.pdf |
| Summary: | We present 2 years of NO<sub><i>x</i></sub> observations from the Cape Verde Atmospheric
Observatory located in the tropical Atlantic boundary layer. We find that
NO<sub><i>x</i></sub> 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 NO<sub>2</sub> to HNO<sub>3</sub>. Production of NO<sub><i>x</i></sub> via
decomposition of organic nitrogen species and the photolysis of HNO<sub>3</sub>
appear insufficient to provide the observed noontime maximum. A rapid
photolysis of nitrate aerosol to produce HONO and NO<sub>2</sub>, however, is able
to simulate the observed diurnal cycle. This would make it the dominant
source of NO<sub><i>x</i></sub> at this remote marine boundary layer site, overturning the
previous paradigm according to which the transport of organic nitrogen
species, such as PAN, is the dominant source. We show that observed
mixing ratios (November–December 2015) of HONO at Cape Verde
(∼ 3.5 pptV peak at solar noon) are consistent with this route for
NO<sub><i>x</i></sub> production. Reactions between the nitrate radical and halogen
hydroxides which have been postulated in the literature appear to improve the
box model simulation of NO<sub><i>x</i></sub>. This rapid conversion of aerosol phase
nitrate to NO<sub><i>x</i></sub> changes our perspective of the NO<sub><i>x</i></sub> cycling chemistry
in the tropical marine boundary layer, suggesting a more chemically complex
environment than previously thought. |
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| ISSN: | 1680-7316 1680-7324 |