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    Chlorine activation within urban or power plant plumes: Vertically resolved ClNO2 and Cl-2 measurements from a tall tower in a polluted continental setting
    (Amer Geophysical Union, 2013) Riedel, Theran P.; Wagner, Nicholas L.; Dube, William P.; Middlebrook, Ann M.; Young, Cora J.; Öztürk, Fatma
    Nitryl chloride (ClNO2) is a chlorine atom source and reactive nitrogen reservoir formed during the night by heterogeneous reactions of dinitrogen pentoxide on chloride-containing aerosol particles. The main factors that influence ClNO2 production include nitrogen oxides, ozone, aerosol surface area, soluble chloride, and ambient relative humidity. Regions with strong anthropogenic activity therefore have large ClNO2 formation potential even inland of coastal regions due to transport or local emissions of soluble chloride. As part of the Nitrogen, Aerosol Composition, and Halogens on a Tall Tower field study, we report wintertime vertically resolved ClNO2 and molecular chlorine (Cl-2) measurements taken on a 300 m tall tower located at NOAA's Boulder Atmospheric Observatory in Weld County, CO, during February and March of 2011. Gas and particle phase measurements aboard the tower carriage allowed for a detailed description of the chemical state of the nocturnal atmosphere as a function of height. These observations show significant vertical structure in ClNO2 and Cl-2 mixing ratios that undergo dynamic changes over the course of a night. Using these measurements, we focus on two distinct combustion plume events where ClNO2 mixing ratios reached 600 and 1300 parts per trillion by volume, respectively, aloft of the nocturnal surface layer. We infer ClNO2 yields from N2O5-aerosol reactions using both observational constraints and box modeling. The derived yields in these plumes suggest efficient ClNO2 production compared to the campaign average, where in-plume yields range from 0.3 to 1; the campaign average yield in the boundary layer is 0.05 +/- 0.15, with substantial night-to-night and within night variability similar to previous measurements in this region.
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    Vertically resolved chemical characteristics and sources of submicron aerosols measured on a Tall Tower in a suburban area near Denver, Colorado in winter
    (Amer Geophysical Union, 2013) Öztürk, Fatma; Bahreini, R.; Wagner, Nicholas L.; Dube, W. P.; Young, Cora J.; Brown, S. S.; Brock, Charles A.
    The Nitrogen, Aerosol Composition, and Halogens on a Tall Tower study was conductedat the Boulder Atmospheric Observatory in Colorado during February–March 2011. Acompact time-of-flight aerosol mass spectrometer was installed in a moving carriage on thetower, obtaining vertical profiles of submicron nonrefractory aerosol mass concentrations(PMnr1)from0–265 m above ground level. The average PMnr1was 4.6 ± 5.7 μg/m3, withaverage contributions of nitrate, organics, sulfate, ammonium, and chloride of 35%, 26%,20%, 17%, and 1%, respectively. Positive Matrix Factorization analysis of the organic aerosol(OA) mass spectra indicated that average contributions of oxygenated organic aerosol(OOA)-I, OOA-II, and hydrocarbon-like organic aerosol (surrogates for aged and freshsecondary OA and primary OA, respectively) to OA mass were 52%, 32%, and 16%,respectively. There was considerable variability in the vertical profiles of aerosol mass loadingand composition, especially at the lowest heights. Below 40 m, the highest PMnr1concentrationswere composed of mostly nitrate (30–46%) and were associated with winds from the northeastwhere there are large agricultural facilities. When winds were southerly, PMnr1massdistributions near the surface had small, fresh OA, indicating the influence of nearby Denverurban emissions at the site. The largest contribution to OA mass at these heights was OOA-II(~43%). Between 40 and 120 m, trajectory cluster analysis indicated that during high-altitudelong-range transport events, daytime aerosol composition was dominated by sulfate, whereasduring low-altitude transport events, the contributions of sulfate, nitrate, and OA werecomparable. OOA-I contributed the most (53–68%) to OA mass at these tower heights.