Acyl peroxy nitrates (APNs) are an important class of reactive nitrogen species formed as a result of photochemical processing of hydrocarbons in the presence of NOx (NOx = NO+NO2). Measurements of speciated acyl peroxy nitrates (APNs) were made from August-October 2007 on a ponderosa pine plantation in the Sierra Nevada Mountains of California during the Biosphere Effects on AeRosols and Photochemistry Experiment (BEARPEX, 2007). Observations of peroxy acetyl nitrate (PAN), peroxy methacryloyl nitrate (MPAN), peroxy propionyl nitrate (PPN) along with OH, NOx and a suite of aldehydes and ketones are used to evaluate a steady state model of APN concentrations. We find that ratios of APNs (e.g., PAN/MPAN, MPAN/PPN) are accurately predicted when temperatures exceed 15 °C. More than 70% of the VOC sources of PAN at the highest temperature are molecules other than acetaldehyde, with the largest contribution from methylvinyl ketone. Other significant sources include methacrolein, methyl glyoxal and biacetyl.