Analysis of stratospheric NO<sub>2</sub> trends above Jungfraujoch using ground-based UV-visible, FTIR, and satellite nadir observations

Abstract

Abstract. The trend in stratospheric NO 2 column at the NDACC (Network for the Detection of Atmospheric Composition Change) station of Jungfraujoch (46.5 • N, 8.0 • E) is assessed using ground-based FTIR and zenith-scattered visible sunlight SAOZ measurements over the period 1990 to 2009 as well as a composite satellite nadir data set constructed from ERS-2/GOME, ENVISAT/SCIAMACHY, and METOP-A/GOME-2 observations over the 1996-2009 period. To calculate the trends, a linear least squares regression model including explanatory variables for a linear trend, the mean annual cycle, the quasi-biennial oscillation (QBO), solar activity, and stratospheric aerosol loading is used. For the 1990-2009 period, statistically indistinguishable trends of −3.7 ± 1.1 % decade −1 and −3.6 ± 0.9 % decade −1 are derived for the SAOZ and FTIR NO 2 column time series, respectively. SAOZ, FTIR, and satellite nadir data sets show a similar decrease over the 1996-2009 period, with trends of −2.4 ± 1.1 % decade −1 , −4.3 ± 1.4 % decade −1 , and −3.6 ± 2.2 % decade −1 , respectively. The fact that these declines are opposite in sign to the globally observed +2.5 % decade −1 trend in N 2 O, suggests that factors other than N 2 O are driving the evolution of stratospheric NO 2 at northern mid-latitudes. Possible causes of the decrease in stratospheric NO 2 columns have been investigated. The most likely cause is a change in the NO 2 /NO partitioning in favor of NO, due to a possible stratospheric cooling and a decrease in stratospheric chlorine content, the latter being further confirmed by the negative trend in the ClONO 2 column derived from FTIR observations at Jungfraujoch. Decreasing ClO concentrations slows the NO + ClO → NO 2 + Cl reaction and a stratospheric cooling slows the NO + O 3 → NO 2 + O 2 reaction, leaving more NO x in the form of NO. The slightly positive trends in ozone estimated from ground-and satellitebased data sets are also consistent with the decrease of NO 2 through the NO 2 + O 3 → NO 3 + O 2 reaction. Finally, we cannot rule out the possibility that a strengthening of the Dobson-Brewer circulation, which reduces the time available for N 2 O photolysis in the stratosphere, could also contribute to the observed decline in stratospheric NO 2 above Jungfraujoch.

Hemispheric asymmetry in stratospheric NO<sub>2</sub> trends

“…This formula has previously been used for trends in NO 2 (Van der A et al, 2006(Van der A et al, , 2008Hendrick et al, 2012).…”

“…Such models have been extensively used in recent years to infer trends in long-term atmospheric time series of groundbased instruments; in particular, they have been used to study the evolution of stratospheric ozone (Bodeker et al, 1998;Wohltmann et al, 2007;Fioletov, 2008;Mäder et al, 2010), NO 2 ( Van der A et al, 2006Van der A et al, , 2008Gruzdev, 2009;Hendrick et al, 2012) and other species (i.e. Remsberg, 2015).…”

Intercomparison of stratospheric nitrogen dioxide columns retrieved from ground-based DOAS and FTIR and satellite DOAS instruments over the subtropical Izana station

“…A positive trend was found over the middle latitudes of the Southern Hemisphere, in good agreement with expectations, whereas the trend over the Northern Hemisphere was negative, in disagreement with the increase of emissions of nitrous oxide (N 2 O), which is a precursor of NO 2 . Hendrick et al (2012) also found negative trends over Jungfraujoch for the period 1990-2009. Gil-Ojeda et al (2015) found a hemispherical and latitude dependence on the sign and magnitude of the trend based on four GB DOAS stations.…”

“…Large differences in AVK profiles between DOAS, FTIR and satellite techniques would lead to uncertainties difficult to quantify and could result in a more complicated intercomparison (Adams et al, 2012;Dirksen et al, 2011;Hendrick et al, 2012;Peters et al, 2012;Sussmann et al, 2005, among others). This, however, is not the case.…”

“…They showed that the mean deviation between the FTIR measurements and MIPAS from July 2002 until March 2004 remains within 10 % in Kiruna (68 • N) and over Harestua (60 • N) a mean negative bias of 15 % have been presented for MIPAS UV-vis daytime comparisons. Hendrick et al (2012) compared stratospheric NO 2 datasets from the DOAS-based instrument SAOZ and FTIRbased instrument Bruker with satellite DOAS instruments, namely GOME, SCIAMACHY and GOME-2, at northern midlatitudes over Jungfraujoch from 1990 to 2009. They observed FTIR minus GB DOAS mean relative differences of about −7.8 ± 8.2 % and satellite minus GB DOAS mean relative differences of 0.9 ± 8.8 % for GOME, 1.9 ± 11.5 % for SCIAMACHY and 2.3 ± 11.6 % for GOME-2.…”