Summertime NOy speciation at the Jungfraujoch, 3580 m above sea level, Switzerland

During summer 1997, speciated reactive nitrogen (NO, NO2, peroxyacetyl nitr ate (PAN), HNO3, and particulate nitrate) was measured in conjunction with total reactive nitrogen (NOy) at the high-alpine research station Jungfrauj och (JFJ), 3580 m above sea level (asl). The individually NOy components av eraged to 82% of total NOy. PAN was the most abundant reactive nitrogen com pound and composed on average 36% of NOy, followed by NOx (22%), particulat e nitrate (17%), and HNO3 (7%). The NOx/NOy ratio averaged 0.25, but signif icantly lower values (0.15-0.20) were observed in the presence of high NOy mixing ratios. A classification of the data by synoptic weather conditions indicated that thermally driven vertical transport has a strong impact on t he mixing ratios measured at the JFJ during summer. A strong diurnal cycle with maximum mixing ratios in the late afternoon was observed for convectiv e days with north-westerly advection at 500 hPa. In contrast, during a peri od of convective days with a wind speed below 7.5 m s(-1) at 500 hPa, no ob vious 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 t o the free troposphere and hence influence global atmospheric chemistry.