Pan over the Arctic; Observations during AGASP-2 in April 1986

During three of the flights with the NOAA P3 Orion over the Arctic icecap in April 1986, the atmospheric concentration of PAN (peroxyacetyl nitrate) was measured. Due to major experimental problems, the uncertainty in the data is large (+/–50%), but, nevertheless, some important trends can be resolved. More than 600 (+/–300) ppt(v) of PAN was present in a moderately dense arctic haze layer, confirming conclusions reached from surface observations at Alert, N.W.T., Canada, that PAN is a major odd nitrogen species in Arctic polluted air masses. In relatively clean air off Barrow, Alaska, PAN levels were well below 100 (+/–50) ppt(v), increasing with altitude, in agreement with theoretical predictions concerning the occurrence of PAN in clean air. PAN mixing ratios in the upper troposphere or lower stratosphere were variable (from ca. 30 (+/–15) ppt(v) on April 13 up to 140 (+/–70) ppt(v) on April 8), suggesting involvement in the tropospheric-stratospheric exchange of odd nitrogen. To place the PAN data in a broader context, measurements of other NO_y compounds as well as integrated SO_x data are also reported.