Peroxcarboxylic Nitric Anhydrides (PANs) are important by-products of hydrocarbon (HC)-NOx photochemistry. The most abundant compound, peroxyacetic nitric anhydride (PAN) is correlated with O₃ in urban and regionally polluted atmospheres. Relative concentrations of the minor PANs; peroxypropionic nitric anhydride (PPN), peroxymethacrylic nitric anhydride (MPAN), peroxyisobutyric nitric anhydride (PiBN) can be used to indicate the origin of HCs that participated in O₃ formation. The measurements at the La Porte supersite were conducted between August 15 and September 13, 2000. The PANs measured during that time revealed several things; high ozone events were associated with anthropogenic hydrocarbons, and only minor biogenic hydrocarbon chemistry was observed and was not associated with high O₃. A new PAN compound, peroxyacrylic nitric anhydride (APAN), was observed in abundances up to 30% of PAN. This compound is thought to result from local chemistry involving petrochemical sources of 1,3-butadiene and acrolein.