Articles | Volume 16, issue 18
Atmos. Chem. Phys., 16, 12039–12058, 2016
Atmos. Chem. Phys., 16, 12039–12058, 2016

Research article 27 Sep 2016

Research article | 27 Sep 2016

Impacts of the Denver Cyclone on regional air quality and aerosol formation in the Colorado Front Range during FRAPPÉ 2014

Kennedy T. Vu1, Justin H. Dingle1, Roya Bahreini1,2, Patrick J. Reddy3,a, Eric C. Apel3, Teresa L. Campos3, Joshua P. DiGangi4, Glenn S. Diskin4, Alan Fried5, Scott C. Herndon6, Alan J. Hills3, Rebecca S. Hornbrook3, Greg Huey7, Lisa Kaser3, Denise D. Montzka3, John B. Nowak6, Sally E. Pusede8, Dirk Richter5, Joseph R. Roscioli6, Glen W. Sachse9, Stephen Shertz3, Meghan Stell3, David Tanner7, Geoffrey S. Tyndall3, James Walega5, Peter Weibring5, Andrew J. Weinheimer3, Gabriele Pfister3, and Frank Flocke3 Kennedy T. Vu et al.
  • 1Environmental Toxicology Graduate Program, University of California, Riverside, CA 92521, USA
  • 2Department of Environmental Sciences, University of California, Riverside, CA 92521, USA
  • 3Atmospheric Chemistry Observations & Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO 80301, USA
  • 4Chemistry and Dynamics Branch, NASA Langley Research Center, Hampton, VA 23681, USA
  • 5Institute for Arctic and Alpine Research, University of Colorado, Boulder, CO 80303, USA
  • 6Aerodyne Research, Inc., Billerica, MA 01821, USA
  • 7Department of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30033, USA
  • 8Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904, USA
  • 9National Institute of Aerospace, Hampton, VA 23666, USA
  • avisitor at: NCAR, Boulder, CO 80301, USA

Abstract. We present airborne measurements made during the 2014 Front Range Air Pollution and Photochemistry Experiment (FRAPPÉ) project to investigate the impacts of the Denver Cyclone on regional air quality in the greater Denver area. Data on trace gases, non-refractory submicron aerosol chemical constituents, and aerosol optical extinction (βext) at λ  =  632 nm were evaluated in the presence and absence of the surface mesoscale circulation in three distinct study regions of the Front Range: In-Flow, Northern Front Range, and the Denver metropolitan area. Pronounced increases in mass concentrations of organics, nitrate, and sulfate in the Northern Front Range and the Denver metropolitan area were observed during the cyclone episodes (27–28 July) compared to the non-cyclonic days (26 July, 2–3 August). Organic aerosols dominated the mass concentrations on all evaluated days, with a 45 % increase in organics on cyclone days across all three regions, while the increase during the cyclone episode was up to  ∼  80 % over the Denver metropolitan area. In the most aged air masses (NOx / NOy  <  0.5), background organic aerosols over the Denver metropolitan area increased by a factor of ∼  2.5 due to transport from Northern Front Range. Furthermore, enhanced partitioning of nitric acid to the aerosol phase was observed during the cyclone episodes, mainly due to increased abundance of gas phase ammonia. During the non-cyclone events, βext displayed strong correlations (r  =  0.71) with organic and nitrate in the Northern Front Range and only with organics (r  =  0.70) in the Denver metropolitan area, while correlation of βext during the cyclone was strongest (r  =  0.86) with nitrate over Denver. Mass extinction efficiency (MEE) values in the Denver metropolitan area were similar on cyclone and non-cyclone days despite the dominant influence of different aerosol species on βext. Our analysis showed that the meteorological patterns associated with the Denver Cyclone increased aerosol mass loadings in the Denver metropolitan area mainly by transporting aerosols and/or aerosol precursors from the northern regions, leading to impaired visibility and air quality deterioration.

Short summary
In this manuscript, we report on airborne measurements of non-refractory composition and optical extinction along with relevant trace gases during a unique surface mesoscale circulation event, namely the Denver Cyclone, in Colorado, USA, during in July–August 2014. The focus of this paper is to investigate how meteorological conditions associated with the Denver Cyclone impacted air quality of the Colorado Front Range.
Final-revised paper