At Look Rock, TN, aerosol instruments used for this study were housed in a 20’x20’x8’ container with air conditioning set to 21 °C. The nozzle of the inlet for air sampling was ~5 m AGL and the site was at an elevation of 802 m. Ambient air was pulled isokinetically through the inlet at about 900 L min-1 using a blower to provide sufficient bypass air to keep flow conditions constant [Bates et al., 2004]. Sampled air lines were dried by diffusion driers in the van before distribution to instruments. Teflon filters (Teflo, Gelman Sciences, Ann Arbor, MI) were collected twice per day after a 2.5 μm cyclone (SCC, Rupprecht & Patashnick, East Greenbush, NY) from 0800 to 1900 and from 2000 to 0700 and four per day behind a 1 μm cyclone from 0800 to 1200, from 1200 to 1600, from 1600 to 1900, and from 2000 to 0700. Flow rates were controlled by mass flow controllers at constant volume flow rates (MCR-100SLPM, Alicat, Tucson, AZ) and recorded. A Bruker Tensor 27 FTIR spectrometer with a deuterated triglycine sulfate (DTGS) detector (Bruker, Waltham, MA) was used to scan the filters both before and after sampling. Filters were loaded each morning and solenoid valves controlled the start and stop of collection; the filter holders were mounted in a 5 ft3 refrigerator to keep the filter holders at 4℃ during and after collection each day to minimize losses due to vaporization of higher vapor pressure components and reactions that could change organic composition during storage. An automated algorithm was then applied to quantify the mass of the organic functional groups [Russell et al., 2009; Takahama et al., 2013]. Five functional groups are presented in the paper: Alkane, Amine, Alcohol, Carbonyl and Carboxylic acid groups. Other groups (Organosulfate, Organonitrate, Aromatic and Alkene group) were also fit but more than 80% of the samples were below detection limit. 42 of the Teflon filters were selected for X-ray fluorescence (XRF) (Chester Labnet, OR) of major elements above 23 amu. The mass of dust was calculated from the metals on these filters by assuming the dust is composed of Na2O, MgCO3, Al2O3, SiO2, K2O, CaCO3, TiO2, Fe2O3, MnO and BaO [Usher et al., 2003].
View this collection on the contributor's website.