A dual flame photometric detector for measurement of SO2 and aerosol sulfur from aircraft platforms has been developed. Mass-flow controllers are used to maintain a constant flow of sample air and hydrogen to the FPD burners as altitude varies. This eliminates the variation in the sulfur signal with altitude usually observed in conventional designs and greatly reduces the altitude variation in the flame background signal. Sulfur dioxide and aerosol sulfur are differentiated by placing a quartz filter before the SO2 detector and a litharge denuder before the aerosol sulfur detector. Sensitivity of the detector is enhanced by use of hydrogen doped with 100 ppb SF6. Performance of the instrument during pressure chamber tests and on test flights is discussed.

Principles involved in the measurement of sulfur concentrations using a flame photometric detector (FPD) are described along with factors other than sulfur which affect FPD response. Variations in inlet pressure and sample water vapor concentration are both shown to alter zero air response and instrument calibration to SO2. Daily atmospheric fluctuations in barometric pressure and water partial pressure are found to significantly affect low-level (< 20 ppb) measurements. Possible solutions to these problems investigated in this paper include an inlet drying system, mass flow control and increased sensitivity through sulfur addition to the hydrogen stream. The FPD exhibits no detectable change in sensitivity up to an altitude of 1400 m when the mass flows of air and H2 are held constant although a slight increase in baseline response is observed. The use of a 66 ppb SF6-H2 mixture results in a 13-fold increase in signal/noise at 1 ppb and lowers the limit of detection for sulfur to about 0.1 ppb.

A system for measurement of ambient levels of aerosol sulfur using a flame photometric sulfur analyzer (FPD) with a heated denuder for SO2 removal has been developed. Cyclic addition of ammonia permits discrimination between sulfuric acid and other sulfate aerosols. The effects of changes in ambient water vapor concentration and barometric pressure on the FPD sulfur response have been quantitatively evaluated, and it is shown that other environmental effects on sulfur response may be eliminated by frequent and proper zeroing. Calibration plots and ambient data are presented which demonstrate the specificity and sensitivity of the system to < 1.0 ppb aerosol sulfur.

Cellulose filters impregnated with NaCl will collect nitric acid vapor from ambient atmospheres at efficiencies of ~95% when placed downstream from pretreated quartz particle filters in a high-volume sampler. No adsorption of NO2 on the NaCl filters with retention as nitrate was observed. Conversion of NO2 to nitrate on quartz (either retained as nitrate or released as artifact nitric acid) was negligibly low with the removal of the less than 1% of the incident NO2. At high humidities adsorption of HNO3 on the quartz prefilter can become significant Quartz filters which were preloaded with ambient particulate matter lost nitrate when exposed to aerosol H2SO4. Sulfur dioxide may be collected on potassium-carbonate-impregnated cellulose filters placed downstream from quartz and NaCl papers without any loss on the preceding filters. Ammonium nitrate on quartz filters is partially volatilized during ambient air sampling.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPolyene-ML2 and -ML4 complexes. Conformational preferences and barriers of rotationThomas A. Albright, Roald Hoffmann, Yuk-Ching Tse, and Ted D'OttavioCite this: J. Am. Chem. Soc. 1979, 101, 14, 3812–3821Publication Date (Print):July 1, 1979Publication History Published online1 May 2002Published inissue 1 July 1979https://pubs.acs.org/doi/10.1021/ja00508a018https://doi.org/10.1021/ja00508a018research-articleACS PublicationsRequest reuse permissionsArticle Views188Altmetric-Citations74LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts