Document Type


Publication Date


Publication Title

Atmospheric Chemistry and Physics









Summertime aerosol optical extinction (βext) was measured in the Colorado Front Range and Denver metropolitan area as part of the Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) campaign during July–August 2014. An Aerodyne cavity attenuated phase shift particle light extinction monitor (CAPS-PMex) was deployed to measure βext (at average relative humidity of 20 ± 7 %) of submicron aerosols at λ = 632 nm at 1 Hz. Data from a suite of gas-phase instrumentation were used to interpret βext behavior in various categories of air masses and sources. Extinction enhancement ratios relative to CO (Δβext ∕ ΔCO) were higher in aged urban air masses compared to fresh air masses by  ∼  50 %. The resulting increase in Δβext ∕ ΔCO for highly aged air masses was accompanied by formation of secondary organic aerosols (SOAs). In addition, the impacts of aerosol composition on βext in air masses under the influence of urban, natural oil and gas operations (O&G), and agriculture and livestock operations were evaluated. Estimated non-refractory mass extinction efficiency (MEE) values for different air mass types ranged from 1.51 to 2.27 m2 g−1, with the minimum and maximum values observed in urban and agriculture-influenced air masses, respectively. The mass distribution for organic, nitrate, and sulfate aerosols presented distinct profiles in different air mass types. During 11–12 August, regional influence of a biomass burning event was observed, increasing the background βextand estimated MEE values in the Front Range.


Justin H. Dingle1, Kennedy Vu1, Roya Bahreini1,2, Eric C. Apel3, Teresa L. Campos3, Frank Flocke3, Alan Fried4, Scott Herndon5, Alan J. Hills3, Rebecca S. Hornbrook3, Greg Huey6, Lisa Kaser3, Denise D. Montzka3, John B. Nowak5, Mike Reeves3, Dirk Richter4, Joseph R. Roscioli5, Stephen Shertz3, Meghan Stell3, David Tanner6, Geoff Tyndall3, James Walega4, Petter Weibring4, and Andrew Weinheimer3

1Environmental Toxicology Graduate Program, University of California, Riverside, CA 92521, USA
2Department of Environmental Sciences, University of California, Riverside, CA 92521, USA
3National Center for Atmospheric Research, Boulder, CO 80301, USA
4Institute for Arctic and Alpine Research, University of Colorado, Boulder, CO 80303, USA
5Aerodyne Research, Inc., Billerica, MA 01821, USA
6Department of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA 30033, USA