Calibration and detection techniques for trace nitrogen compounds in the atmosphere | Posted on:1991-01-05 | Degree:Ph.D | Type:Dissertation | University:University of Maryland, College Park | Candidate:Nunnermacker, Linda Jean | Full Text:PDF | GTID:1478390017950854 | Subject:Chemistry | Abstract/Summary: | | Simultaneous measuremnts of NO, NOx, and NOy were made during an instrument intercomparison between the University of Maryland and the NOAA Aeronomy Laboratory. The NOy measurements used a gold catalyst at 300{dollar}spcirc{dollar}C (NOAA) or a molybdenum catalyst at 400{dollar}spcirc{dollar}C (UMD); NOx measurements involved photolysis of NO{dollar}sb2{dollar} (NOAA) or reduction of NO{dollar}sb2{dollar} by solid ferrous sulfate (FeSO{dollar}sb4){dollar}. The two instruments agreed on daytime (NO) to the limit of detection (25 pptv), and gave similar estimates of NOy concentrations. Ferrous sulfate exhibited a significant interference from PAN and apparently n-propyl nitrate.; Further tests of the UMD NOx and NOy measurement techniques were made in the laboratory. The conversion efficiencies of NO{dollar}sb2{dollar}, HNO{dollar}sb3{dollar}, and several alkyl nitrates were studied as a function of temperature on stainless steel and molybdenum. Potential interferences (NH{dollar}sb3{dollar}, HCN, and CH{dollar}sb3{dollar}CN) were also studied. NOy compounds tested on a Mo converter at 375{dollar}spcirc{dollar}C under humidified conditions exhibited the optimum conversion efficiencies with negligible interferences. The FeSO{dollar}sb4{dollar} converter reduced only NO{dollar}sb2{dollar} (and PAN) to NO with high efficiency. Nylon filters were found to selectively scrub HNO{dollar}sb3{dollar} (HONO was not tested).; A new calibration source of gaseous HNO{dollar}sb3{dollar} was developed, based on the reaction of HCl(g) with AgNO{dollar}sb3{dollar}(s). The concentration of HNO{dollar}sb3{dollar} produced by the system was determined using three independent techniques: tunable diode laser absorption spectroscopy, chemiluminescence detection, and ion chromatography. At 40{dollar}spcirc{dollar}C, the system converts HCl to nearly pure HNO{dollar}sb3{dollar} with 92 to 100% efficiency. Dynamic dilution was used to obtain HNO{dollar}sb3{dollar} concentrations of 9 ppbv.; A dual-converter (Mo) technique was used to measure NOy and (HNO{dollar}sb3{dollar} + NO{dollar}sb3sp-{dollar}) in August and September, 1989. One converter measured NOy while the second used a Nylon filter at the inlet to remove HNO{dollar}sb3{dollar} vapor and particulate nitrate. The difference between the two signals yields a measure of total nitrate. Both the instrument response and zero were determined daily using the HCl/AgNO{dollar}sb3{dollar} calibration system ((HNO{dollar}sb3{dollar}) = 9 ppbv). The average ambient concentrations were (NOy) = 2.42 {dollar}pm{dollar} 1.28 ppbv and (total nitrate) = 1.01 {dollar}pm{dollar} 0.81 ppbv (dry conditions). | Keywords/Search Tags: | Noy, Hno{dollar}sb3{dollar}, Calibration, Detection, Techniques, Nitrate, Ppbv | | Related items |
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