Photochemistry of an Urban Region using Observations and Numerical Modeling

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Christopher A Cantrell1, Lee Mauldin2, Anondo D Mukherjee2, Frank M Flocke3, Gabriele Pfister3, Eric C Apel4, Roya Bahreini5, Donald Ray Blake6, Nicola J Blake7, Teresa Lynn Campos3, Ronald C Cohen8, Delphine Farmer9, Alan Fried1, Alex B Guenther6, Samuel R Hall3, Brian Heikes10, Rebecca S Hornbrook3, L Gregory Huey11, Thomas Karl12, Lisa Kaser3, John B Nowak13, John Victor Ortega3, Daniel W O'Sullivan14, Dirk Richter15, James N Smith6, David Tanner16, Amy Townsend-Small17, Kirk Ullmann3, James Walega15, Petter Weibring15, Andrew John Weinheimer3 and FRAPPE/DISCOVER-AQ Science Team, (1)Univ of Colorado, Boulder, CO, United States, (2)University of Colorado at Boulder, Boulder, CO, United States, (3)National Center for Atmospheric Research, Boulder, CO, United States, (4)University Corporation for Atmospheric Research, Boulder, CO, United States, (5)University of California Riverside, Riverside, CA, United States, (6)University of California Irvine, Irvine, CA, United States, (7)University California Irvine, Vineyard Haven, MA, United States, (8)University of California Berkeley, Berkeley, CA, United States, (9)Colorado State University, Fort Collins, CO, United States, (10)URI GSO, Narragansett, RI, United States, (11)Georgia Institute of Technology, Atlanta, GA, United States, (12)University of Innsbruck, Institute for Meteorology and Geophysics, Innsbruck, Austria, (13)Aerodyne Research Inc., Billerica, MA, United States, (14)US Naval Academy, Annapolis, MD, United States, (15)University of Colorado at Boulder, INSTAAR, Boulder, CO, United States, (16)Georgia Tech, Atlanta, GA, United States, (17)University of Cincinnati, Cincinnati, OH, United States
The chemistry of HOx radicals in the troposphere can lead to the production of secondary products such as ozone and aerosols, while volatile organic compounds are degraded. The production rates and identities of secondary products depend on the abundance of NOx and other parameters. The amounts of VOCs and NOx can also affect the concentrations of OH, HO2 and RO2. Comparison of observations and model-derived values of HOx species can provide one way to assess the completeness and accuracy of model mechanisms. The functional dependence of measure-model agreement on various controlling parameters can also reveal details of current understanding of photochemistry in urban regions.

During the Front Range Air Pollution and Photochemistry Experiment (FRAPPE), conducted during the summer of 2014, observations from ground-based and airborne platforms were performed to study the evolution of atmospheric composition over the Denver metropolitan area. Of particular interest in FRAPPE was the assessment of the roles of mixing of emissions from oil and gas exploration and extraction, and those from confined animal production operations, with urban emissions (e.g. from transportation, energy production, and industrial processes) on air quality in the metropolitan and surrounding region.

Our group made measurements of OH, HO2, and HO2 + RO2 from the NSF/NCAR C-130 aircraft platform using selected ion chemical ionization mass spectrometry. The C-130 was equipped with instrumentation for the observation of a wide variety of photochemical-related species and parameters. These data are used to assess the photochemical regimes encountered during the period of the study, and to quantitatively describe the chemical processes involved in formation of secondary products. One of the tools used is a steady state model for short-lived species such as those that we observed.

This presentation summarizes the behavior of species that were measured during FRAPPE and what the observations reveal about urban photochemistry in a higher altitude metropolitan area such as Denver. The analysis of the data and the model representations lead to quantitative assessment of current understanding of tropospheric chemical processes in such environments.