United States Environmental Protection Agency Environmental Sciences Research Laboratory Research Triangle Park NC 27711 Research and Development EPA-600/S3-83-105 Jan. 1984 Project Summary Intercomparison of Periodic Fine Particle Sulfur and Sulfate Concentration Results David C. Camp, Richard J. Paur, and Robert K. Stevens A one-week study was conducted in August 1979 to evaluate the compar- ative ability of representative aerosol sampling systems to monitor fine partic- ulate sulfur and sulfate concentrations periodically in situ. Participants in the study operated their samplers simulta- neously in the same location for the duration of the study. Samplers tested included five modified flame photomet- ric detection instruments and two di- chotomous samplers, including one sampler designed to yield near-real-time sulfur concentrations from on-line, wave- length dispersive x-ray fluorescence analysis of fine particles collected on Teflon substrate. All but one of the samplers were operated from a common duct located within the same laboratory; the other was operated on the roof of the building. Normalized results of all sulfur con- centration levels measured for five of the six samplers were 1.0 ± 0.05. The sixth set gave a result of 0.60 ±0.14. After revised results were resubmitted for the sixth set, normalized results for the six sets of hourly sulfur results agreed to within ± 8% of their composite- mean values, with standard deviations varying from 9 to 22%. One participat- ing group operated three similar sam- plers, each calibrated by a different method, that gave normalized results of 1.06 ± 0.12, 0.93 ± 0.22, and 1.54± 0.25; these results point out the need for a standard calibration procedure. This Project Summary was developed by EPA's Environmental Sciences Re- search Laboratory, Research Triangle Park, NC, to announce key findings of the research project that is fully docu- mented in a separate report of the same title (see Project Report ordering infor- mation at back). Introduction In August 1979, a one-week study was conducted at Washington University, St. Louis, to compare a family of air pollution monitoring instruments that are capable of measuring in near-real-time atmos- pheric concentrations of aerosol sulfur. The main objective of this study was to compare different procedures to measure aerosol sulfur that use flame photometric detectors (FPD's) and an automated semi- real-time x-ray fluorescence (XRF) aero- sol sample-analyzer. The instruments that use the FPD's have been used in a variety of air pollution studies, but be- cause each instrument uses a different method of sample conditioning prior to the sulfur measurement, bias in the measurements may exist. This study compared measurements of different automated aerosol sulfur monitors on both simulated and real ambient air samples over a period of 7 days to establish the range of differences be- tween instruments and the basis for variations in response characteristics. Procedure Analyzers brought to Washington Uni- versity by the seven participating groups included five modified FPD instruments and two dichotomous samplers. One dichotomous sampler was designed to report near-real-time sulfur concentra- tions from an on-line, wavelength dis- persive, XRF analysis of the fine particles collected on a filter substrate. All sam- ------- piers were operated simultaneously, and all but one operated from a common duct leading to a common laboratory. The inlet to the common duct contained an impac- tor plate particle-sizing device that re- jected all particles greater than 3.0 (jm in aerodynamic diameter. The sampler not using the common duct was operated on the roof above the laboratory. Results Concentration of the sulfur measured during the study by the participants consisted of eight sets of hourly fine pa rticulate sulfur values. Only six of eight sets were intercompared. One of the participating groups reported three sets of sulfur data based on three different calibrations methods. Ambient sulfur concentrations measured during the study ranged from just below 1 /ug/m3 to 9 fjg/m3. Above 6 //g/m3 the five FPD instruments and the automated XRF sulfur analyzer intercompared agreed to within ± 25% of their combined compos- ite-mean concentrations. Five of the six agreed to within ± 5% of the composite- mean values. All of the automated FPD instruments were able to resolve and measure the relatively sharp sulfur con- centration peaks that occurred daily. The source and nature of these short, some- times multi-peaked, excursions were not investigated. Three sets of 6-h sulfate concentra- tions were reported and intercompared. Their concentrations varied from about 2 fjg/m3 to 20 jug/m3. At relatively high sulfate concentrations (> 14 /jg/m3) all three samplers agreed to within ± 10% of their composite 6-h means. Regression analysis of 6-h composite-mean sulfate concentrations, derived from ion chromat- ographic analysis of fine particles col- lected with a dichotomous sampler, vs. equivalent 6-h averages for the hourly sulfur composite-mean values gave a sulfate-to-sulfur ratio of 2.2 for the St. Louis study vs. 3.0 observed in two earlier studies. This ratio remained at 2.2 for both clean and stagnant air and during the transient sulfur excursions. Thus, either all of the sulfur did not occur in sulfate form or the sulfate could not be extracted completely from the filter-types used by all three independent groups. Three sampling systems operated by the host institution provided results based on three different calibration methods. Their results based on an (NH4)2S04 calibration were closest to the composite mean average (1.06 ± 0.12—an average of all hourly results normalized to the hourly composite-mean values); whereas the sulfur monitors that used S02 for calibration differed substantially from the composite mean (1.54 ± 0.25). If either of the two worst-result sets of the eight sets submitted had been the only set of sulfur concentrations measured, the report* hourly sulfur concentrations would somi times have been as much as a factor of higher or lower than the consensi composite-mean concentrations from tr six sets intercompared. Conclusions and Recommendations Measurements obtained from FPDsy; terns modified to measure aerosol sulfi and calibrated by appropriate procedure agreed within ± 8% with the composii mean. Data from FPD's calibrated usir (NH4)2SO4 had less scatter and were i closer agreement to the composite mea average than data from FPD analyzei calibrated using SO2. A standard ASTN type aerosol calibration procedure neec to be developed and documented f< routine calibration of instruments usedl measure in near-real-time ambient cor centrations of aerosol sulfur. David C. Camp is a Consultant at 258 Paraiso Drive, Danville, CA 94526; the EPA authors, Richard J. Paur and Robert K. Stevens (also the EPA Project Officer, see below) are with Environmental Sciences Research Laboratory, Research Triangle Park, NC 27711. The complete report, entitled "Intercomparison of Periodic Fine Particle Sulfur and Sulfate Concentration Results," (Order No. PB84-119 940; Cost: $10.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Environmental Sciences Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 «US. 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