Chemical Characteristics and Ozone Production in the Northern Colorado Front Range. Issue 23 (3rd December 2019)

• Record Type: Journal Article
• Authors: Pfister, Gabriele; Wang, Chi‐Tsan; Barth, Mary; Flocke, Frank; Vizuete, William; Walters, Stacy
• Is Part Of: Journal of geophysical research. Volume 124:Issue 23(2019)
• Page Start: 13397
• Page End: 13419
• Publication Date: 2019-12-03
• Subjects: ozone chemistry -- air quality -- chemical modeling -- Field campaigns -- Colorado Front Range; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2019JD030544
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: We use the extensive set of aircraft and ground‐based observations from the NSF/National Center for Atmospheric Research (NCAR) and State of Colorado Front Range Air Pollution and Photochemistry Éxperiment and the NASA DISCOVER‐AQ experiments in summer 2014 together with the regional chemical transport model Weather Research and Forecast Model with Chemistry (WRF‐Chem) to study the ozone production and chemical regimes in the Northern Colorado Front Range (NFR). We apply the model's Integrated Reaction Rate capability and chemical tendencies diagnostics and present results from an in‐depth analysis of the ozone formation in various NFR regions for a case study of 12 August 2014. We further apply these diagnostics along a WRF online trajectory to assess the chemical evolution of an airmass during transport. The results show efficient ozone production within the NFR driven by the availability of NO x and an abundance of highly reactive volatile organic compound and also continued ozone production during the transport into the mountains. We identify CO, formaldehyde, higher alkanes, acetaldehyde, and isoprene among the volatile organic compound species with the highest efficiency in ozone production. Formaldehyde and acetaldehyde concentrations in the NFR have a significant contribution from photochemical production, which in turn is linked back to methane oxidation and to emissions of higher alkanes, isoprene, ethane, and propane. This study provides valuable policy information into the chemical fingerprint of surface ozone in the NFR, an area that is in nonattainment of the U.S. EPA ozone health standards and demonstrates the capability of the newly added diagnostic tool in WRF‐Chem to address the drivers behind secondary production of pollutants in greater detail. Plain Language Summary: The Colorado Northern Front Range (NFR) frequently exceeds national health standards for ozone. Understanding the reasons behind these trends and how they relate to local emissions is crucial for developing control strategies. Using measurements from two major field campaigns in summer 2014 together with chemical transport modeling, we show that ozone is produced efficiently within the NFR driven by availability of local NO x and an abundance of highly reactive volatile organic compounds (VOCs). On high ozone days, upslope flows are frequent and ozone continues to be produced during transport of air from the NFR into the mountains with ozone values in the pristine areas sometimes exceeding NFR values. Chemical analysis shows that key VOCs include carbon monoxide, formaldehyde, higher alkanes, acetaldehyde, and isoprene. Higher alkanes and isoprene are related to direct emissions from oil and natural gas activities and to direct emissions from biogenic sources, respectively. A small part of ambient concentrations of formaldehyde and acetaldehyde is related to direct emissions, but the dominant part is produced photochemically from methane oxidation and emissions of higher alkanes, isoprene, ethane, and propane. Knowledge about the role of different VOC precursors provides valuable information to policy makers and helps develop efficient and cost‐effective control strategies. Key Points: Efficient ozone production is driven by availability of local NOx and highly reactive VOCs and continues during the transport into mountains Key species driving ozone production include CO, formaldehyde, higher alkanes, acetaldehyde, and isoprene Most of formaldehyde and acetaldehyde is chemically produced and due to methane oxidation and emissions of higher alkanes, isoprene, and ethane