• New instrumentation for the detection of sulfur dioxide in the remote atmosphere

      Nicks, Dennis Keith, Jr.; Benner, Richard (1999)
      Sulfur gases are an important chemical component of the atmosphere. Gaseous sulfur compounds effect the acidity of rainwater and are important precursors to aerosol particles which affect public health, climate and visibility of scenic vistas such as the Grand Canyon. Sulfate aerosols are also known to participate in ozone catalysis in the stratosphere. A vast majority of the gaseous sulfur cycling through the atmosphere will exist as sulfur dioxide (SO2) at some time during its atmospheric lifetime. Since SO 2 is a primary component of the atmospheric sulfur cycle, quality measurements of this gas are important to understanding the cycling of sulfur through the atmosphere. The mixing ratio of SO2 in the atmosphere can be as low as a few 10's of parts-per-trillion by volume (pptv) in unpolluted areas and as high as 100's of parts-per-billion by volume (ppbv) near industrial centers. Obtaining SO2 measurements with mixing ratios that can differ by 105 in magnitude is a difficult task, especially for mixing ratios less than a few hundred pptv. The Diffusion Denuder/Sulfur Chemiluminescence Detector (DD/SCD) was developed further and tested in a rigorously blind comparison under controlled laboratory conditions. The DD/SCD exhibited excellent sensitivity and little-to-no interference from other trace gases. The DD/SCD performance was comparable to that of other state-of-the-art instruments developed for measuring SO 2 in the remote atmosphere. The Continuous SO2 Detector was developed to overcome the limitation of long sampling times (4 to 90 minutes) inherent in the DD/SCD and other state-of-the-art techniques. The Continuous SO2 Detector (CSD) was developed based on the design of the DD/SCD, but has been optimized for sensitive, high-time resolved measurements of SO2 in air. Sensitive, high-time resolved measurements would be beneficial for studying atmospheric SO2 over large geographical areas from a moving sampling platform such as an aircraft. The current prototype of the CSD is capable of measuring SO2 at mixing ratios of less than 100 pptv on the order of seconds. The DD/SCD, CSD and an automated, computer controlled dynamic dilution system described in this thesis represent a suite of instruments for the measurement of SO2 in the remote atmosphere.
    • Nitrogen oxides in the Arctic troposphere

      Honrath, Richard Edward, Jr.; Jaffe, Daniel A.; Gosnick, Joan P.; Stolzberg, Richard J.; Stamnes, Knut; Shaw, Glenn E. (1991)
      Nitrogen oxides play a critical role in tropospheric photochemistry. In order to characterize these compounds in the arctic troposphere, ground-level concentrations of total reactive nitrogen (NO$\sb{y}$) and NO were determined over an extended period at a site near Barrow, Alaska. A high-sensitivity instrument developed for this purpose was used in three measurement campaigns: summer 1988, spring 1989, and March-December 1990. During the 1990 campaign, the detection limit for NO was 3-10 pptv (depending on averaging period), and the NO$\sb{y}$ uncertainty was $\pm$26%. A screening algorithm was applied to the data to eliminate effects from local (Barrow) sources, and the remaining data were divided into "background periods" (unaffected by local or regional NO$\sb{x}$ sources), and "events" (periods when emissions from a regional NO$\sb{x}$ source--the Prudhoe Bay oil-producing region--apparently impacted Barrow). These measurements revealed a sharp seasonal cycle of background NO$\sb{y}$ concentrations, with high values in early spring (median 560-620 pptv) and $\sim$70 pptv (median) during summer. This cycle is similar to that of other compounds in arctic haze but is partially attributed to a reduction in NO$\sb{y}$ lifetime due to organic nitrate decomposition as temperatures and insolation increased. Evidence indicates that the springtime arctic NO$\sb{y}$ reservoir was primarily composed of stable removal-resistant species, including PAN and other organic nitrates. PAN decomposition as temperatures rose in late spring likely caused an observed pulse of NO to $\sim$35 pptv (maximum hourly average); hourly-average NO concentrations were otherwise generally $<$8 pptv. NO$\sb{x}$ production from PAN decomposition due to the onset of spring or southward advection may affect springtime O$\sb3$ levels both in the Arctic and in the northern mid-latitudes. NO$\sb{y}$ and O$\sb3$ concentrations were positively correlated during summer, possibly indicating long-range transport of both and/or the presence of a mid-tropospheric NO$\sb{y}$ reservoir combined with a stratospheric O$\sb3$ source. A number of events with substantially elevated NO$\sb{y}$ concentrations (to 16 ppbv) were observed in air not impacted by emissions from the town of Barrow. Substantial evidence indicates that these events were a result of NO$\sb{x}$ emissions from the Prudhoe Bay region ($\sim$300 km to the ESE), which is also expected to affect measurements of other compounds at the Barrow site.