Leonard Stockburger

Investigation of hydroxyl radical reactions with o-xylene and m-xylene in a continuous stirred tank reactor

The gas-phase reactions of hydroxyl radicals with o-xylene and m-xylene were studied in a continuous stirred tank reactor. Gas and aerosol products accounted for 65-85% of the reacted carbon. Approximately 19 and 13% of the original o-xylene and m-xylene oxidation were estimated to have occurred through methyl hydrogen abstraction by OH, primarily leading to methylbenzyl nitrates and tolualdehydes. The remaining mass reacted through the OH addition pathway forming dimethylphenols, nitrodimethylphenols, nitroxylenes, and stable products resulting from reaction of metastable O/sub 2/-OH adducts. For o-xylene, the ratio of the rate constants for formation of nitroxylenes vs. dimethylphenols was estimated to be 5.9 x 10/sup 4/, while the same value for m-xylene was only about 1.0 x 10/sup 4/. The ratios of the dimethylphenol formation rates to the oxygen addition rates were found to be greater than or equal to 0.15 for o-xylene and 0.27 for m-xylene. 44 references, 3 figures, 4 tables.

Intercomparison of nitric acid diffusion denuder methods with tunable diode laser absorption spectroscopy

Abstract Three diffusion denuder techniques for measurement of nitric acid were compared to result s from a tunable diode laser absorption system. Also all techniques were compared to the median value. Gaseous nitric acid was measured in the effluent stream of a continuous stirred tank reactor. The nitric acid was generated photochemically with a hydrocarbon/ NO x /air mixture. Linear regression analysis showed the short configuration nylon diffusion denuder systems compared very well with the HNO 3 results of the laser system. The long configuration nylon and tungstic acid diffusion denuder systems gave much lower values with more variability.

Trueness, precision, and detectability for sampling and analysis of organic species in airborne particulate matter

Recovery, precision, limits of detection and quantitation, blank levels, calibration linearity, and agreement with certified reference materials were determined for two classes of organic components of airborne particulate matter, polycyclic aromatic hydrocarbons and hopanes, using typical sampling and gas chromatography/mass spectrometry analysis methods. These determinations were based on initial method proficiency tests and on-going internal quality control procedures. Recoveries generally ranged from 75% to 85% for all target analytes and collocated sample precision estimates were generally better than 20% for polycyclic aromatic hydrocarbons and better than 25% for hopanes. Results indicated substantial differences in data quality between the polycyclic aromatic hydrocarbons and hopanes. Polycyclic aromatic hydrocarbons demonstrated better collocated precision, lower method detection limits, lower blank levels, and better agreement with certified reference materials than the hopanes. The most serious area of concern was the disagreement between measured and expected values in the standard reference material for hopanes. With this exception, good data quality was demonstrated for all target analytes on all other data quality indicators.

Comparison of sulfur measurements from a regional fine particle network with concurrent acid modes network results

Abstract The Fine Particle Network (FPN), a system of fine particle (less than 2.5 μm) samplers, was operated at 41 sites selected from the Environment Protection Agency Acid MODES program during a two-year period in 1988–1990. The 24-h sample results included fine particle mass and the most predominant chemical element concentrations determined by wavelength dispersive X-ray fluorescence analysis. Statistical summaries of the fine mass and sulfur concentrations by site and season were prepared. The sulfur