Peroxycarboxylic nitric anhydrides (PANs) were measured at Cornelia Fort Airpark during the 1999 Nashville Intensive of the Southern Oxidants Study. The observed concentrations were similar to those measured in the 1994 and 1995 Nashville Intensives. The average daytime ratio of peroxypropionic nitric anhydride (PPN) to peroxyacetic nitric anhydride (PAN) was 13.7%. Extensive measurements were also made of peroxyisobutyric nitric anhydride (PiBN), which confirm the anthropogenic origin of this compound, and its ratio to PAN was 2.4% on average. The daytime ratio of peroxymethacrylic nitric anhydride (MPAN) to PAN was as high as 25% during periods of high biogenic hydrocarbon (BHC) impact. A simple linear combination model was used to estimate anthropogenic hydrocarbon (AHC) and BHC contributions to O3 production. On average, 80% of the O3 observed over 80 ppbv was attributed to AHC chemistry and 20% to BHC chemistry. An exception to this was a plume derived from a combination of power plant NOx and isoprene emissions from west of the city, in which the BHC contribution was at least 50 to 75%.