A12A-06
Summertime Acyl peroxy nitrates (PANs) in the Colorado Front Range

Monday, 14 December 2015: 11:35
3010 (Moscone West)
Jake Zaragoza1, Emily V Fischer1, Erin E. McDuffie2, William P Dube3, Steven S Brown3, Delphine Farmer4 and Frank M Flocke5, (1)Colorado State University, Atmospheric Science, Fort Collins, CO, United States, (2)University of Colorado at Boulder, Boulder, CO, United States, (3)NOAA Boulder, Boulder, CO, United States, (4)Colorado State University, Fort Collins, CO, United States, (5)National Center for Atmospheric Research, Boulder, CO, United States
Abstract:
The Colorado Front Range (CFR) currently violates the 8-hour National Ambient Air Quality Standard for ozone (O3). The Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) was an extensive aircraft and ground-based campaign aimed at characterizing the regional chemical environment in the CFR. Campaign goals were to constrain the emissions of O3 precursors and the subsequent O3 formation rates. A large suite of trace gases and aerosols were measured during FRAPPÉ at the Boulder Atmospheric Observatory (BAO), including O3, NOx, NOy, CH4, CO, CO2, and several PAN homologues. The BAO, located 35 km north of Denver and on the southwestern side of the Denver-Julesburg Basin, affords the opportunity to sample a wide variety of air masses, including those impacted by emissions from oil and gas development, agriculture, and the urban Denver plume.

Here we present an analysis of PAN measurements during FRAPPÉ. The PPN/PAN ratio observed (~20%) at BAO during FRAPPÉ is indicative of chemistry dominated by anthropogenic VOCs. We used the relationships between PAN, PPN, and MPAN to estimate the contribution of isoprene chemistry to local O3 production. We found that the estimated contribution of isoprene chemistry to O3 is less than 5 ppbv. We also investigated the meteorological conditions leading to the most extreme PAN abundances. We found that Denver Cyclones, mesoscale conditions that allow for potential recirculation of pollutants, were present on three out of the four days with PAN mixing ratios much greater than 1 ppbv. We plan to continue exploring specific days characterized by measurements of elevated PAN and O3 with a photochemical box model to attempt to understand the mix of VOC chemistry responsible for the extremely consistent observed PPN/PAN ratio.

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