Observations of acyl peroxy nitrates during the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ)

We report on measurements of acyl peroxy nitrates (APNs) obtained from two ground sites and the NSF/National Center for Atmospheric Research C-130 aircraft during the 2014 Front Range Air Pollution and Photochemistry Experiment (FRAPPE). The relative abundance of the APNs observed at the Boulder Atmospheric Observatory (BAO) indicates that anthropogenic emissions of volatile organic compounds (VOCs) are the dominant drivers of photochemistry during days with the most elevated peroxyacetyl nitrate (PAN). Reduced major axis regression between propionyl peroxynitrate (PPN) and PAN observed at BAO and from the C-130 produced a slope of 0.21 (R-2=0.92). Periods of lower PPN/PAN ratios (similar to 0.10) were associated with cleaner background air characterized by lower ammonia and formic acid abundances. The abundance of methacryloyl peroxynitrate relative to PAN only exceeded 0.05 at BAO when PAN mixing ratios were <300parts per trillion by volume, implying low influence of isoprene oxidation during periods with substantial local PAN production. We show an example of a day (19 July) where high O-3 was not accompanied by enhanced local PAN production. The contribution of biogenic VOCs to local O-3 production on the other days in July with elevated O-3 (22, 23, 28, and 29 July 2014) was small; evidence is provided in the high abundance of PPN to PAN (slopes between 0.18 and 0.26). The PAN chemistry observed from surface and aircraft platforms during FRAPPE implies that anthropogenic VOCs played a dominant role in PAN production during periods with the most O-3 and that the relative importance of biogenic hydrocarbon chemistry decreased with increasing O-3 production during FRAPPE.