RELATIONSHIPS BETWEEN PEROXYACETYL NITRATE, O-3, AND NOY AT THE RURAL SOUTHERN OXIDANTS STUDY SITE IN CENTRAL PIEDMONT, NORTH-CAROLINA, SITE SONIA

Ambient peroxyacetyl nitrate (PAN) concentrations were measured during June and early July 1992 at site SONIA (Southeast Oxidants and Nitrogen Intensive Analysis), a rural site in the central Piedmont region of North Carolina, as part of the Southern Oxidants Study. PAN measurements were made as part of an effort to provide a comprehensive chemical climatology and to investigate the total nitrogen budget at this site. Gas chromatograph-electron capture detector (GC-ECD) was used to measure PAN every 15 min with a detection limit of 50 parts per trillion by volume. During the measurement period, maximum ambient levels of PAN reached 1.2 parts per billion by volume and averaged 0.41 +/- 0.24 ppbv (n=1972) with an average daily maximum of 0.60 ppbv. The average daytime (0900-2100 EST) concentration was 0.52 +/- 0.24 ppbv (n=986) while the average nighttime (2100-0900) concentration was 0.29 +/- 0.07 ppbv (n=986). The O-3/PAN ratio was found to be 138 +/- 98 (n=984) and the PAN/NOy ratio was 0.12 +/- 0.11 (n=454). Hourly average PAN and O-3 concentrations showed a strong correlation with R=0.57 (n=984). Moreover, the composite hourly averages of PAN and O-3 for the entire measurement period showed an even stronger correlation of R=0.95. The strong correlation between O-3 and PAN suggest that mesoscale photochemical production plays a major role in PAN chemistry at site SONIA. An analysis of 10 m meteorological data suggests some correlation between regional meteorological conditions and between both the daily PAN maxima and the magnitude of the O-3/PAN ratio.