Relationships between peroxyacetyl nitrate, O₃, and NO_y at the rural Southern Oxidants Study site in central Piedmont, North Carolina, site SONIA

Abstract

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/NO y 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.