Impacts of the Denver Cyclone on Regional Air Quality and Aerosol Formation in the Colorado Front Range during FRAPPÉ 2014

We present airborne measurements made in the Colorado Front Range aboard the NSF C-130 aircraft during the 2014 Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ) project. Data on trace gases, non-refractory sub-micron aerosol chemical constituents, and aerosol optical extinction (βext) at λ = 632 nm in the presence and absence of a surface mesoscale circulation pattern, called the Denver Cyclone, were analyzed in three study regions of the Front Range: In-Flow, Northern Front Range (NFR), and Denver Metropolitan (DM). Pronounced increases in mass concentrations of organics, nitrate, and sulfate in NFR and DM were observed during the cyclone episodes (27–28 July) compared to the non-cyclonic days (26 July, 02–03 August). Organics (OA) dominated the mass concentrations on all evaluated days, with a 45 % increase in OA on cyclone days across all three regions while the increase during the cyclone episode was up to ~ 80 % for DM, from 3.78 ± 1.55 µg sm−3 to 6.78 ± 1.78 µg sm−3, where sm−3 is the STP unit of volume of air. Average nitrate mass concentrations were 0.26 ± 0.27 µg sm−3 vs. 1.03 ± 0.74 µg sm−3 followed by sulfate with an average of 0.58 ± 0.23 µg sm−3 vs. 1.08 ± 0.73 µg sm−3 on non-cyclone vs. cyclonic days, respectively. In the most aged air masses (NOx/NOy