An experimental and numerical study of the thermal oxidation of chlorobenzene

A combustion-driven flow reactor was used to examine the formation of chlorinated and non-chlorinated species from the thermal oxidation of chlorobenzene under post-flame conditions. Temperature varied from 725 to 1000 K, while the equivalence ratio was held constant at 0.5. Significant quantities of chlorinated intermediates, vinyl chloride and chlorophenol, were measured. A dominant C-Cl scission destruction pathway seen in pyrolytic studies was not observed. Instead, hydrogen-abstraction reactions prevailed, leading to high concentrations of chlorinated byproducts. The thermal oxidation of benzene was also investigated for comparison. Chemical kinetic modeling of benzene and chlorobenzene was used to explore reaction pathways. Two chlorobenzene models were developed to test the hypothesis that chlorobenzene oxidation follows a CO-expulsion breakdown pathway similar to that of benzene. For the temperatures and equivalence ratio studied, hydrogen abstraction by hydroxyl radicals dominates the initial destruction of both benzene and chlorobenzene. Chlorinated byproducts (i.e., chlorophenol and vinyl chloride) were formed from chlorobenzene oxidation in similar quantities and at similar temperatures to their respective analogue formed during benzene oxidation (i.e., phenol and ethylene).     

A Fuel-Based Assessment of Off-Road Diesel Engine Emissions

ABSTRACT

The use of diesel engines in off-road applications is a significant source of nitrogen oxides (NO_x) and particulate matter (PM₁₀). Such off-road applications include railroad locomotives, marine vessels, and equipment used for agriculture, construction, logging, and mining. Emissions from these sources are only beginning to be controlled. Due to the large number of these engines and their wide range of applications, total activity and emissions from these sources are uncertain. A method for estimating the emissions from off-road diesel engines based on the quantity of diesel fuel consumed is presented. Emission factors are normalized by fuel consumption, and total activity is estimated by the total fuel consumed.

Total exhaust emissions from off-road diesel equipment (excluding locomotives and marine vessels) in the United States during 1996 have been estimated to be 1.2 × 10⁹ kg NO_x and 1.2 x 10⁸ kg PM₁₀. Emissions estimates published by the U.S. Environmental Protection Agency are 2.3 times higher for both NO_x and exhaust PM₁₀ emissions than estimates based directly on fuel consumption. These emissions estimates disagree mainly due to differences in activity estimates, rather than to differences in the emission factors. All current emission inventories for off-road engines are uncertain because of the limited in-use emissions testing that has been performed on these engines. Regional- and state-level breakdowns in diesel fuel consumption by off-road mobile sources are also presented. Taken together with on-road measurements of diesel engine emissions, results of this study suggest that in 1996, off-road diesel equipment (including     

Excimer laser fragmentation-fluorescence spectroscopy as a method for monitoring ammonium nitrate and ammonium sulfate particles

Excimer laser fragmentation-fluorescence spectroscopy (ELFFS) is shown to be an effective detection strategy for ammonium nitrate and ammonium sulfate particles at atmospheric pressure and room temperature. Following photofragmentation of the ammonium salt particle, fluorescence of the NH fragment is observed at 336 nm. The fluorescence signal is shown to depend linearly on particle surface area for laser intensities varying from 1.2 x 10(8) to 6 x 10(8) W/cm2. The 100 shot (1 s) detection limits for ammonium nitrate range from 20 ppb for 0.2 microm particles to 125 ppb for 0.8 microm particles, where these concentrations are expressed as moles of ammonium ion per mole of air. For ammonium sulfate, the 100 shot (1 s) detection limits vary from 60 ppb for 0.2 microm particles to 500 ppb for 1 microm particles. These detection limits are low enough to measure ammonium salt particles that form in the exhaust of combustion processes utilizing ammonia injection as a nitric oxide control strategy.     

Building a better methane generation model: Validating models with methane recovery rates from 35 Canadian landfills

The German EPER, TNO, Belgium, LandGEM, and Scholl Canyon models for estimating methane production were compared to methane recovery rates for 35 Canadian landfills, assuming that 20% of emissions were not recovered. Two different fractions of degradable organic carbon (DOC_f) were applied in all models. Most models performed better when the DOC_f was 0.5 compared to 0.77. The Belgium, Scholl Canyon, and LandGEM version 2.01 models produced the best results of the existing models with respective mean absolute errors compared to methane generation rates (recovery rates + 20%) of 91%, 71%, and 89% at 0.50 DOC_f and 171%, 115%, and 81% at 0.77 DOC_f. The Scholl Canyon model typically overestimated methane recovery rates and the LandGEM version 2.01 model, which modifies the Scholl Canyon model by dividing waste by 10, consistently underestimated methane recovery rates; this comparison suggested that modifying the divisor for waste in the Scholl Canyon model between one and ten could improve its accuracy. At 0.50 DOC_f and 0.77 DOC_f the modified model had the lowest absolute mean error when divided by 1.5 yielding 63 ± 45% and 2.3 yielding 57 ± 47%, respectively. These modified models reduced error and variability substantially and both have a strong correlation of r = 0.92.     

In situ push-pull method to determine ground water denitrification in riparian zones

To quantify ground water denitrification in discrete locations of riparian aquifers, we modified and evaluated an in situ method based on conservative tracers and 15N-enriched nitrate. Ground water was "pushed" (i.e., injected) into a mini-piezometer and then "pulled" (i.e., extracted) from the same mini-piezometer after an incubation period. This push-pull method was applied in replicate mini-piezometers at two Rhode Island riparian sites, one fresh water and one brackish water. Conservative tracer pretests were conducted to determine incubation periods, ranging from 5 to 120 h, to optimize recovery of introduced plumes. For nitrate push-pull tests, we used two conservative tracers, sulfur hexafluoride and bromide, to provide insight into plume recovery. The two conservative tracers behaved similarly. The dosing solutions were amended with 15N-enriched nitrate that enabled us to quantify the mass of denitrification gases generated during the incubation period. The in situ push-pull method detected substantial denitrification rates at a site where we had previously observed high denitrification rates. At our brackish site, we found high rates of ground water denitrification in marsh locations and minimal denitrification in soils fringing the marsh. The push-pull method can provide useful insights into spatial and temporal patterns of denitrification in riparian zones. The method is robust and results are not seriously affected by dilution or degassing from ground water to soil air. In conjunction with measurements of ground water flow-paths, this method holds promise for evaluating the influence of site and management factors on the ground water nitrate removal capacity of riparian zones.     

CONSERVATION PRACTICES AND ATTITUDES AMONG MARYLAND WATER SUPPLY MANAGERS1

ABSTRACT: In addition to offsetting water supply shortages, water conservation is recognized as serving many purposes, ranging from reduced energy consumption to lower capital costs. Since the discussion of these benefits has been a recent development and has generally excluded local water supply managers, a question arises as to whether supply managers are implementing conservation programs to exploit these benefits. A survey of the managers at 35 Maryland water utilities provides insight into the prevailing attitude toward conservation in a water rich eastern state. The results indicate that most managers continue to view conservation only as a short term response to temporary supply shortages. Only 12 Maryland utilities have undertaken any form of water conservation activity and just two systems have ongoing, comprehensive conservation programs. Institutional, perceptual, economic, political, and time constraints all contribute to the managers’attitudes and general inaction. If water conservation is to be widely practiced, these issues must be addressed and the benefits attributed to conservation must be better documented and articulated to supply managers.