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

Abstract

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