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Acyl peroxy nitrates (APNs, also known as PANs) are formed from theoxidation of aldehydes and other oxygenated VOC (oVOC) in the presence ofNO2. There are both anthropogenic and biogenic oVOC precursors to APNs,but a detailed evaluation of this chemistry against observations has provenelusive. Here we describe measurements of PAN, PPN, and MPAN along with themajority of chemicals that participate in their production and loss,including OH, HO2, numerous oVOC, and NO2. Observations were madeduring the Biosphere Effects on AeRosols and Photochemistry Experiment(BEARPEX 2007) in the outflow of the Sacramento urban plume. Theseobservations are used to evaluate a detailed chemical model of APN ratiosand concentrations. We find that the ratios of APNs are nearly independentof the loss mechanisms and thus an especially good test of our understandingof their sources. We show that oxidation of methylvinyl ketone,methacrolein, methyl glyoxal, biacetyl and acetaldehyde are all significantsources of the PAN+peroxy acetyl (PA) radical reservoir, accounting for26%, 2%, 7%, 20%, and 45%, of the production rate on averageduring the campaign, respectively. At high temperatures, when upwindisoprene emissions are highest, oxidation of non-acetaldehyde PA radicalsources contributes over 60% to the total PA production rate, withmethylvinyl ketone being the most important of the isoprene-derived sources.An analysis of absolute APN concentrations reveals a missing APN sink thatcan be resolved by increasing the PA+∑RO2 rate constant by afactor of 3

Closing the peroxy acetyl nitrate budget: observations of acyl peroxy nitrates (PAN, PPN, and MPAN) during BEARPEX 2007