Peroxyacetic Nitric Anhydride, and PAN

J. Roberts
NOAA Aeronomy Lab

and

F. Flocke
National Center for Atmospheric Research

Peroxyacetic nitric anhydride, PAN is often the dominant NOy species in the remote troposphere. It is relatively insoluble in aqueous solution and is thermally stable at low temperatures (lifetime = 20 days at 263 ^oK). As discussed earlier in the text, a major atmospheric question as related to Antarctic nitrogen is : what are the primary sources of reactive nitrogen? PAN, which has significant biomass burning sources in the SH, may be one such primary source. It is also possible, however, due to what appears to be intense chemistry in interstitial air within the snowpack, that PAN may also be formed on the plateau. Measurements of PAN are now scheduled for the first deployment at SP in 2003. Both atmospheric sampling as well as exploratory snow sampling will be undertaken.
The measurement of PAN will be accomplished using capillary gas chromatography with electron capture detection (GC/ECD). Samples will be taken by direct injection of small volume (2 ambient cc) of air onto a megabore capillary column. PAN type compounds are separated during a 5 minute chromatographic run, and the cycle is then repeated. Calibrations are performed automatically every 5 hours by injecting a standard into ambient air from which PAN has been removed by treatment of the ambient air stream at elevated temperature (125 ^oC). The standard stream is produced by the high efficiency conversion (95%) of a known nitric oxide concentration to PAN using acetone/CO photochemistry. This calibration method is cross-checked from time-to time using a diffusion source of PAN in tridecane/pentadecane solution that is calibrated by NOy conversion. The detection limit of the GC technique is 5pptv, and the combined uncertainties are of the order of ±(5 pptv +15%). Other PAN type compounds can be observed with this system, if present, with similar sensitivity.