Articles | Volume 14, issue 22
Research article
28 Nov 2014
Research article |  | 28 Nov 2014

Analysis of elevated springtime levels of Peroxyacetyl nitrate (PAN) at the high Alpine research sites Jungfraujoch and Zugspitze

S. Pandey Deolal, S. Henne, L. Ries, S. Gilge, U. Weers, M. Steinbacher, J. Staehelin, and T. Peter

Abstract. The largest atmospheric peroxyacetyl nitrate (PAN) mole fractions at remote surface sites in the Northern Hemisphere are commonly observed during the months April and May. Different formation mechanisms for this seasonal maximum have previously been suggested: hemispheric-scale production from precursors accumulated during the winter months, increased springtime transport from up-wind continents or increased regional-scale production in the atmospheric boundary layer from recent emissions. The two high Alpine research sites Jungfraujoch (Switzerland) and Zugspitze (Germany) exhibit a distinct and consistent springtime PAN maximum. Since these sites intermittently sample air masses of free-tropospheric and boundary layer origin, they are ideally suited to identify the above-mentioned PAN formation processes and attribute local observations to these. Here we present a detailed analysis of PAN observations and meteorological conditions during May 2008 when PAN levels were especially elevated at both sites. The highest PAN concentrations were connected with anticyclonic conditions, which persisted in May 2008 for about 10 days with north-easterly advection towards the sites. A backward dispersion model analysis showed that elevated PAN concentrations were caused by the combination of favourable photochemical production conditions and large precursor concentrations in the European atmospheric boundary layer. The results suggest that the largest PAN values in spring 2008 at both sites were attributable to regional-scale photochemical production of PAN in the (relatively cold) planetary boundary layer from European precursors, whereas the contribution of inter-continental transport or free-tropospheric build-up was of smaller importance for these sites.

Short summary
Mixing ratios of Peroxyacetyl nitrate (PAN) at Jungfraujoch (Switzerland) and Zugspitze (Germany) show a seasonal variation with maxima in spring, typical for remote sites in the lower atmosphere in northern mid-latitudes. The detailed analysis of PAN measurements of May 2008 indicates that PAN at these high mountain sites is dominated by photochemical formation in the relatively cold polluted European planetary boundary layer rather than formation in the free troposphere.
Final-revised paper