Donald L. Fox

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.

STATISTICAL APPROACHES IN WIND SECTOR ANALYSES FOR ASSESSING LOCAL SOURCE IMPACTS

Abstract Nonparametric statistical methods were used as part of a wind sector analysis assessment for the purpose of investigating local source impacts. Linear-angular rank correlations were employed to test for the presence of association between pollutant tracer concentrations and wind direction for a local area dominated by a single emission source (a biomedical waste combustor). Testing for the presence of these associations in ambient data from a local area likely to include multiple pollutant sources (including a resource recovery facility) was accomplished using the nonparametric Kruskal-Wallis test. Modified pollutant wind rose plots were used to qualitatively investigate the nature of the associations detected using these statistical tests, focusing on the sources of interest known to emit the pollutant tracers-of-opportunity. The statistical methods presented provide a quantitative basis for the assessment of source impacts based on observed associations between wind direction and pollutant concentrations.

Aircraft and air pollution

The Clean Air Act of 1977 directs EPA to issue emission standards for aircraft engines that may contribute to air pollution and thus endanger public health or welfare. Critics argue that the regulations are overly complex and stringent, and that immediate energy shortages may take precedence over the need for aircraft emission controls. Proponents of the regulations claim that ambient air standards are freqeuntly violated and will continue to be unless the best available control technology is applied to all sources, including aircraft. The contribution of aircraft to total emissions is discussed. Engineering problems and costs of retrofitting pollution controls on aircrafts are examined.

The influence of molecular complexes on the photooxidation of sulfur dioxide

Abstract It is proposed that molecular interaction products and specifically donor-acceptor molecular complexes significantly affect SO2 photochemical reaction mechanisms. Product quantum yield and triplet SO2 quenching rates are related to the extent of complex formation as indicated by the ionization potential and dielectric constant of the donor species. Intra-complex rearrangement may lead to some of the reaction products observed in some studies. Molecular complexes appear to participate in aerosol formation mechanisms involving SO2. NO and various hydrocarbons at ambient levels.

Design and Operating Parameters for a Large Ambient Aerosol Chamber

Recent investigations of ambient aerosol behavior over urban areas have pointed out the need for controlled experimental data to link together field investigation results and computer simulation studies. This paper describes the design considerations, construction details and operating parameters of a large (8000 ft3) outside reaction chamber constructed in rural North Carolina. The chamber is triangular in cross-section, 20 ft wide, 20 ft high and 40 ft long, and is covered with clear 5 ml Teflon film. The outdoor location of the chamber permits the reaction volume to be exposed to the natural conditions of temperature and solar radiation. A recirculating air system allows the air in the chamber to be passed through an “absolute” fiberglas filter for adjustment of condensation nuclei concentration and also through driers for humidity adjustment. Internal fans are provided for mixing of the chamber contents without use of the recirculating system so that various degrees of turbulence can be approximated. ...

The Transformation of Pollutants

Publisher Summary This chapter discusses the transformation of pollutants. The atmosphere is composed principally of nitrogen, oxygen, and water vapor. All other gases are considered as trace gases. The sources of these gases are based at the earths surface or in the atmosphere as a transformation product of a surface released gas. By dividing trace gas sources into anthropogenic and natural categories, the relative importance of mans activities on a meso- or global scale could be understood. Anthropogenic, or man-made, sources are dominated by the use of energy for home heating, hot water, and industrial processes, such as converting raw materials into consumer products. The major man-made source categories are fossil fuel combustion for power generation and transportation, chemical processes, petroleum recovery, refining, and distribution. Natural sources might be subdivided into releases from physical or biological processes. Two of the physical processes entail venting of gases from the earths crust in the form of volcanic eruptions and volatile hydrocarbon seepage. Biological processes include fermentation, denitrification, and terpene release from vegetation. Society can alter natural emission patterns by converting tropical rain forests to agricultural land. Estimates on a global scale compare anthropogenic and natural sources of various trace gases.

The effect of CO on sulfate aerosol formation

Abstract A series of experiments were performed in an outdoor smog chamber to determine the effect of CO on the rate of SO2 oxidation in a rural air photochemical system. The presence of added CO, at concentrations ranging from 15 to 30 ppm, decreased the aerosol formation rate as measured by a condensation nuclei counter, an electrical aerosol analyzer, and X-ray fluorescence (XRF) analysis of collected aerosol. Enhanced O3 production due to the action of CO was also detected in one of the experiments. Comparison of the XRF data with results of a photochemical model shows good agreement concerning the effect of CO on the SO2 oxidation rate. This agreement supports the hypothesis that SO2 is oxidized principally by the hydroxyl and hydroperoxy radicals in the system studied.

Photochemical Conversion of NO to NO2 by Hydrocarbons in an Outdoor Chamber

Significant differences occur between results of chamber work conducted outdoors versus work conducted indoors under constant light intensity. Under outdoor conditions at constant (NO/sub x/)/sub 0/, lower (HC)/sub 0/ resulted in lower (NO/sub 2/)/sub max/ and NO/sub 2/ dosage during the daylight hours. The percent reduction in (NO/sub 2/)/sub max/ was a function of the (HC)/sub 0/ reduction and the (NO/sub x/)/sub 0/ level. Under all experimental conditions the 10 hour NO/sub 2/ average to maximum NO/sub 2/ concentration ratio appeared to be constant at 0.73 during the daylight hours. A regression equation relating (NO/sub x/)/sub max/ to (NO/sub x/)/sub 0/, (HC)/sub 0/, and measures of solar radiation accounted for 92% of the variance in the data. Although there is unavoidable confoundment between (HC)/sub 0/ and solar radiation, the HC term in this regression equation can introduce +/- 20% change in (NO/sub 2/)/sub max/. This variation can be partially offset or enhanced by variations in solar radiation. 3 references, 6 figures, 4 tables.

Photochemical Smog Systems: Effect of Dilution on Ozone Formation

Dilution of a photochemical system containing hydrocarbons and oxides of nitrogen can lead to higher ozone concentrations than are observed in a static system. This effect was observed in an outdoor smog chamber with a hydrocarbon mix simulating urban systems.