Long-term in situ measurements of NOx and NOy at Jungfraujoch 1998–2009: time series analysis and evaluation

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Pandey Deolal, S. ; Brunner, D. ; Steinbacher, M. ; Weers, U. ; Staehelin, J. (2012)

We present an analysis of the NO<sub>y</sub> (NO<sub>x</sub> + other oxidized species) measurements at the high alpine site Jungfraujoch (JFJ, 3580 m a.s.l.) for the period 1998&ndash;2009, which is the longest continous NO<sub>y</sub> data set reported from the lower free troposphere worldwide. Due to stringent emission control regulations, nitrogen oxides (NO<sub>x</sub>) emissions have been reduced significantly in Europe since the late 1980s as well as during the investigation period. However, the time series of NO<sub>y</sub> at JFJ does not show a consistent trend but a maximum during 2002 to 2004 and a decreasing tendency thereafter. The seasonal cycle of NO<sub>y</sub> exhibits a maximum in the warm season and a minimum in the cold months, opposite to measurements in the PBL, reflecting the seasonal changes in vertical transport and mixing. Except for summer, the seasonal mean NO<sub>x</sub> concentrations at JFJ show a high year-to-year variability which is strongly controlled by short episodic pollution events obscuring any long-term trends. The low variability in mean and median NO<sub>x</sub> values in summer is quite remarkable indicating rapid photochemical conversion of NO<sub>x</sub> to higher oxidized species (NO<sub>z</sub>) of the NO<sub>y</sub> family on a timescale shorter than the time required to transport polluted air from the boundary layer to JFJ. In order to evaluate the quality of the NO<sub>y</sub> data series, an in-situ intercomparison with a second collocated NO<sub>y</sub> analyzer with a separate inlet was performed in 2009&ndash;2010 which showed an overall agreement within 10% including all uncertainties and errors.
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