Aerosol Optical Extinction during the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) 2014 Summertime Field Campaign, Colorado U.S.A.

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Justin Hernandez Dingle1, Kennedy-kiet T Vu1, Roya Bahreini1, Eric C Apel2, Teresa Lynn Campos3, Christopher A Cantrell4, Ronald C Cohen5, Carlena J Ebben5, Frank M Flocke3, Alan Fried4, Scott C. Herndon6, Alan J Hills7, Rebecca S Hornbrook3, L Gregory Huey8, Lisa Kaser3, Lee Mauldin9, Denise D Montzka3, John B Nowak6, Dirk Richter10, Joseph R Roscioli6, Stephen Shertz3, Meghan H Stell3, David Tanner11, Geoffrey S Tyndall12, James Walega10, Petter Weibring10 and Andrew John Weinheimer3, (1)University of California Riverside, Riverside, CA, United States, (2)University Corporation for Atmospheric Research, Boulder, CO, United States, (3)National Center for Atmospheric Research, Boulder, CO, United States, (4)Univ of Colorado, Boulder, CO, United States, (5)University of California Berkeley, Berkeley, CA, United States, (6)Aerodyne Research Inc., Billerica, MA, United States, (7)NCAR, Boulder, CO, United States, (8)Georgia Institute of Technology Main Campus, Atlanta, GA, United States, (9)Pacific Northwest National Laboratory, Richland, WA, United States, (10)University of Colorado at Boulder, INSTAAR, Boulder, CO, United States, (11)Georgia Tech, Atlanta, GA, United States, (12)Natl Ctr Atmospheric Research, Boulder, CO, United States
Aerosol optical extinction (βext) was measured in the Colorado Front Range Denver Metropolitan Area as part of the summertime air quality airborne field campaign to characterize the influence of sources, photochemical processing, and transport of pollution on local air quality. An Aerodyne Cavity Attenuated Phase Shift particle light extinction monitor (CAPS-PMex) was deployed to measure dry βext at λ=632 nm at 1 Hz. Data from a suite of gas-phase instrumentation were used to interpret the βext under various categories of aged air masses and sources. Extinction enhancement ratios of Δβext/ΔCO were evaluated under 3 differently aged air mass categories (fresh, intermediately aged, and aged) to investigate impacts of photochemistry on βext. Δβext/ΔCO was significantly increased in heavily aged air masses compared to fresh air masses (0.17 Mm-1/ppbv and 0.094 Mm-1/ppbv respectively). The resulting increase in Δβext/ΔCO under heavily aged air masses was represented by secondary organic aerosols (SOA) formation. Aerosol composition and sources from urban, natural oil and gas wells (OG), and agriculture and livestock operations were also evaluated for their impacts on βext. Linear regression fits to βext vs. organic aerosol mass showed higher correlation coefficients under the urban and OG plumes (r=0.55 and r=0.71 respectively) and weakest under agricultural and livestock plumes (r=0.28). The correlation between βext and nitrate aerosol mass however was best under the agriculture and livestock plumes (r=0.81), followed by OG plumes (r=0.74), suggesting co-location of aerosol nitrate precursor sources with OG emissions. Finally, non-refractory mass extinction efficiency (MEE) was analyzed. MEE was observed to be 1.37 g/m2 and 1.30 g/m2 in OG and urban+OG plumes, respectively.