Summertime NO_<i>y</i> speciation at the Jungfraujoch, 3580 m above sea level, Switzerland

Abstract

During summer 1997, speciated reactive nitrogen (NO, NO 2 , peroxyacetyl nitrate (PAN), HNO 3 , and particulate nitrate) was measured in conjunction with total reactive nitrogen (NO y ) at the high‐alpine research station Jungfraujoch (JFJ), 3580 m above sea level (asl). The individually measured NO y components averaged to 82% of total NO y . PAN was the most abundant reactive nitrogen compound and composed on average 36% of NO y , followed by NO x , (22%), particulate nitrate (17%), and HNO 3 (7%). The NO x /NO y ratio averaged 0.25, but significantly lower values (0.15–0.20) were observed in the presence of high NO y mixing ratios. A classification of the data by synoptic weather conditions indicated that thermally driven vertical transport has a strong impact on the mixing ratios measured at the JFJ during summer. A strong diurnal cycle with maximum mixing ratios in the late afternoon was observed for convective days with north‐westerly advection at 500 hPa. In contrast, during a period of convective days with a wind speed below 7.5 m s −1 at 500 hPa, no obvious diurnal cycle was observed. Under these meteorological conditions the convective boundary layer can be significantly higher over the Alps (i.e., around 4 km asl) than over the surrounding lowlands. Subsequent advection may finally result in the export of reactive nitrogen reservoir compounds to the free troposphere and hence influence global atmospheric chemistry.