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Volume 17, issue 21 | Copyright

Special issue: Twenty-five years of operations of the Network for the Detection...

Atmos. Chem. Phys., 17, 13373-13389, 2017
https://doi.org/10.5194/acp-17-13373-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Nov 2017

Research article | 10 Nov 2017

Hemispheric asymmetry in stratospheric NO2 trends

Margarita Yela1, Manuel Gil-Ojeda1, Mónica Navarro-Comas1, David Gonzalez-Bartolomé1, Olga Puentedura1, Bernd Funke2, Javier Iglesias1, Santiago Rodríguez1, Omaira García3, Héctor Ochoa4, and Guillermo Deferrari5,6 Margarita Yela et al.
  • 1Atmospheric Research and Instrumentation Branch. Instituto Nacional de Técnica Aeroespacial (INTA), Ctra. Ajalvir s/n, Torrejón de Ardoz, 28850 Madrid, Spain
  • 2Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain
  • 3Centro de Investigación Atmosférica de Izaña (CIAI), Agencia Estatal de Meteorología (AEMET), Spain
  • 4Dirección Nacional del Antártico/Instituto Antártico Argentino, 25 de Mayo 1143, San Martín Provincia de Buenos Aires, Argentina
  • 5Centro Austral de Investigaciones Científicas (CADIC), Ushuaia, Argentina
  • 6Universidad Nacional de Tierra del Fuego (UNTDF), Ushuaia, Argentina

Abstract. Over 20 years of stratospheric NO2 vertical column density (VCD) data from ground-based zenith DOAS spectrometers were used for trend analysis, specifically, via multiple linear regression. Spectrometers from the Network for the Detection of Atmospheric Composition Change (NDACC) cover the subtropical latitudes in the Northern Hemisphere (Izaña, 28°N), the southern Subantarctic (Ushuaia, 55°S) and Antarctica (Marambio, 64°S, and Belgrano, 78°S). The results show that for the period 1993–2014, a mean positive decadal trend of +8.7% was found in the subtropical Northern Hemisphere stations, and negative decadal trends of −8.7 and −13.8% were found in the Southern Hemisphere at Ushuaia and Marambio, respectively; all trends are statistically significant at 95%. Belgrano only shows a significant decadal trend of −11.3% in the summer/autumn period. Most of the trends result from variations after 2005. The trend in the diurnal build-up per hour (DBU) was used to estimate the change in the rate of N2O5 conversion to NO2 during the day. With minor differences, the results reproduce those obtained for NO2. The trends computed for individual months show large month-to-month variability. At Izaña, the maximum occurs in December (+13.1%), dropping abruptly to lower values in the first part of the year. In the Southern Hemisphere, the polar vortex dominates the monthly distributions of the trends. At Marambio, the maximum occurs in mid-winter (−21%), whereas at the same time, the Ushuaia trend is close to its annual minimum (−7%). The large difference in the trends at these two relatively close stations suggests a vortex shift towards the Atlantic/South American area over the past few years. Finally, the hemispheric asymmetry obtained in this work is discussed in the framework of the results obtained by previous works that considered tracer analysis and Brewer–Dobson circulation. The results obtained here provide evidence that the NO2 produced by N2O decomposition is not the only cause of the observed trend in the stratosphere and support recent publications pointing to a dynamical redistribution starting in the past decade.

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The paper focuses on stratospheric trends of NO2, a species involved in the ozone equilibrium, using data from four NDACC stations. The global stratospheric NO2 trend has not yet been established conclusively. We analyse DOAS data from stations in the Northern Hemisphere and Southern Hemisphere during 1993–2014. The most relevant finding is the hemispheric asymmetry found in the sign of the NO2 trend, providing further evidence of changes in the stratosphere dynamics on the global scale.
The paper focuses on stratospheric trends of NO2, a species involved in the ozone equilibrium,...
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