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Abstract. During summer 1997, speciated reactive nitrogen (NO, NO2, peroxyacetyl nitrate (PAN), HNO3, and particulate nitrate) was measured in conjunction with total reactive nitrogen (NOv) at the high-alpine research station Jungfraujoch (JFJ), 3580 m above sea level (asl). The individually measured NO v components averaged to 82% of total NO v . PAN was the most abundant reactive nitrogen compound and composed on average 36% of NOv, followed by NOx (22%), particulate nitrate (17%), and HNO 3 (7%). The NOx/NOy ratio averaged 0.25, but significantly lower values (0.15-0.20) were observed in the presence of high NO v 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 -• 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.

[1] A comprehensive range of aerosol parameters was measured at an urban and a rural site in the Milan, Italy metropolitan region during summer smog events in summer 1998. Measurements were performed as part of the Pianura Padana Produzione di Ozono (PIPAPO) field campaign to determine the sensitivity of O 3 production to NO X and volatile organic carbon concentrations at several ground stations. Primary aerosol parameters (i.e., direct emissions) such as aerosol black carbon showed a distinct diurnal variation with maxima at about 0000 and 0800 central European summer time (CEST), in contrast to secondary aerosol parameters such as sulfate and nitrate. Aerosol number size distributions were measured under ambient conditions as well as after conditioning with volatility and hygroscopicity systems. A mode at d = 20-30 nm in the number concentration was found at 0800 CEST and exhibited high volatility at 110°C ($80% volume lost upon heating) but no hygroscopic behavior. Based on these measurements, small particles (d < 40 nm) are thought to consist mainly of hydrophobic particulate organic matter, rather than soot or H 2 SO 4 aerosols. Two distinct hygroscopic modes with average growth factors d/d 0 $ 1.02 and 1.21-1.28 were found for particles with dry (relative humidity of <30%) diameters d 0 = 50-200 nm. Submicrometer aerosols exhibited lower volatility at the rural than at the urban site, which is attributed to additional particulate mass produced by secondary particle formation.