Donald L. Singleton

Analysis of Motor Vehicle Sources and Their Contribution to Ambient Hydrocarbon Distributions at Urban Sites In Toronto During the Southern Ontario Oxidants Study

Hydrocarbon distributions measured in the urban area of Toronto during the Southern Ontario Oxidants Study of 1992 are presented. Comparison is made to hydrocarbon distributions measured in other urban areas. Relative concentrations of olefins were found to be depleted aloft compared to the surface level measurements. Chemical mass balance modelling was used to apportion the measured hydrocarbon distributions at York University and other roadside sites to gasoline based sources. The most dominant contributing source was vehicle exhaust. The relative amount of unburned gasoline at York University was found to be significant in the summer, and higher than that observed there during the winter or at other roadside sites. The relative amount of evaporative emissions (gasoline vapour) apportioned by the CMB model at roadside sites was compared to evaporative emissions predicted by a mobile emission factor model, MOBILE5C. The percentage of gasoline based non-methane hydrocarbons (NMHC) apportioned to gasoline vapour by the CMB model was equivalent within error to the relative amount of evaporative NMHC predicted by the MOBILE5C model for summer temperatures. For winter temperatures, the MOBILE5C model predicted significantly less evaporative emissions than that apportioned by the CMB model. An anthropogenic source of isoprene in the urban area has been proposed and tested. The inclusion of an isoprene flux in the exhaust source profile, consistent with that measured in the Auto/Oil Air Quality Improvement Research Program, results in calculated isoprene concentrations that are in agreement with observed concentrations at roadside sites and at York University in the winter. During summer, the combustion related isoprene can only account for a small fraction of the observed isoprene at downtown sites and at York University, at most 20%.

Time‐resolved reflectivity as a probe of the dynamics of laser ablation of organic polymers

The interaction of KrF excimer laser pulses with polyimide, poly(ethylene terephthalate), polystyrene, poly(methyl methacrylate), and polyethylene has been studied by time‐resolved reflectivity. The width, fluence, and peak intensity of a KrF (248 nm) laser pulse reflected from the polymer surface was determined over a large range of incident laser fluences, 1–3000 mJ/cm2. The reflected pulse was truncated once the incident fluence exceeded a critical value (threshold), characteristic for each polymer. Above the threshold the pulse decayed exponentially with time constants ranging from 2 to 6 ns. For polyethylene, such a critical value appears to lie above the highest fluence available in the present experiments. The threshold fluences for pulse truncation are usually somewhat lower than the ablation thresholds measured photoacoustically. The mechanism of the process is discussed in terms of time‐dependent absorption and scattering from particles emerging from the surface during ablation. Approximate calc...

Excimer laser angioplasty: Tissue ablation, arterial response, and fiber optic delivery

The results of recent work directed towards the application of excimer lasers to angioplasty are presented. Several laser-tissue interactions are examined, including the effect of the XeCl laser optical pulse duration (7-300 ns) on the threshold fluence for ablation of arterial wall and on the quality of the cut in human postmortem artery, the potential for altering the ablation threshold fluence of arterial plaque in swine by treatment with hematoporphyrin derivative, and the healing response of swine arterial wall to surgical irradiation with an argon laser and a pulsed XeCl laser. The dependence of damage thresholds and transmission properties of selected commercial fused silica fibers on the laser pulsewidth and wavelength are determined.

Effect of optical pulse duration on the XeCl laser ablation of polymers and biological tissue

Photoacoustic spectroscopy was used to measure the pulse duration dependence of the XeCl laser ablation of polyimide, polyethylene terephthalate, and post‐mortem human aorta. It was observed that the ablation threshold exhibited only a weak dependence on pulse duration. Photoablation etch depth measurements of polyimide as a function of XeCl laser fluence indicated that over a practical etch depth range of 0.1 to 1 μm per laser pulse the etch depth was independent of the pulse duration.

Excimer lasers in cardiovascular surgery: Ablation products and photoacoustic spectrum of the arterial wall

Photoacoustic spectra of normal artery wall and of atherosclerotic plaque are reported. Threshold fluences for ablative formation of gaseous products for each excimer laser line were calculated from the photoacoustic spectrum and the measured threshold for the KrF laser.

The effect of debris formation on the morphology of excimer laser ablated polymers

A study of the distribution of the debris formed by the XeCl laser ablation of polyimide and polyethylene terephthalate and the KrCl laser ablation of polyimide shows that it is the redeposition of debris rather than impurities which accounts for the cone structures commonly seen in the surface morphology.

Sensitivity of ozone concentrations to VOC and NOx emissions in the Canadian Lower Fraser Valley

Abstract The SAPRC90 chemical mechanism module implemented in CALGRID is updated for the specific emissions and applications of the Lower Fraser Valley (LFV) of British Columbia, Canada. The kinetic and mechanistic parameters of lumped VOC reactions recalculated using the LFV emissions profiles are noticeably different from those based on default emissions profiles, indicating the importance of tailoring the parameters to specific regions. The sensitivities of ozone concentrations to total and speciated VOC and NOx emissions as well as to the NO 2 NO x ratios are determined. Significant VOC model species are identified based on the impact of their emissions on ozone formation in the LFV. Of note is the importance of the emissions of a lumped class of aromatics, ARO2, which contains mostly isomers of xylene and trimethylbenzene and is derived chiefly from the use and distribution of gasoline fuels. The ARO2 emissions make the largest contribution of all model VOC species to the ozone levels in the urban plume. The results indicate that reduction of AR02 emissions alone could achieve significant reduction of ozone levels in the LFV. Base case emissions of NOx(NO or NO2) in the LFV contribute negatively to the ozone formation. Any overestimation of NOx or underestimation of VOC in the emissions inventory could cause underestimations of ozone levels by photochemical models.

Temperature dependence of the rate constants for the reactions O(3P) + 2,3‐dimethyl‐2‐butene and O(3P) + NO + M determined by a phase shift technique

Absolute values of the rate constant k2 for the reaction of O(3P) atoms with 2,3‐dimethyl‐2‐butene are determined over the temperature range 298–481 °K using modulated photosensitized decomposition of N2O to generate O(3P) atoms. The rate constants obtained from the phase shift measurements fit the Arrhenius expression, k2 = (1.24±0.12) ×1010 exp(774±76 cal mole−1/RT) in units of l mole−1⋅sec−1. The indicated uncertainties are least squares standard deviations. Possible explanations for the negative Arrhenius activation energy are reviewed. Also, the rate constant k3 for the reaction O(3P) + NO + M is redetermined for M=N2O. Over the temperature range 298–473 °K, the results fit the Arrhenius expression, k3 = (6.12±0.45) ×109 exp(1230±55 cal mole−1/RT), where the units are l2 mole−2⋅sec−1 and the uncertainties are the least squares standard deviations.

Comparison of theoretical models of laser ablation of polyimide with experimental results

Abstract The results of detailed calculations of the etch rates for pulsed UV laser ablation of polyimide at 308 nm using several proposed theoretical models of the process are compared with experimental results. The theories which indicate that the etch depth per pulse is dependent on the fluence, and not the peak intensity of the laser pulse, are consistent with the experimental data for laser pulse widths of 7–500 ns. The implication of the results on various aspects of the models is discussed.

XeCl laser ablation of polyimide: Influence of ambient atmosphere on particulate and gaseous products

The gaseous and particulate products of the XeCl (308 nm) laser ablation of polyimide (Kapton H) are quantitatively determined and compared with the mass loss of the polymer in atmospheres of He, N2, air, or O2. In air and in pure O2, the observed mass balance is about 90%, but is lower for inert atmospheres. With increasing oxygen content in the atmosphere, the yield of CO2 increases at the expense of particulates and acetylene. The influence of laser fluence and nature of the ambient atmosphere on the product distribution is interpreted in terms of ejection of small reactive species which are involved in the competitive reactions of particulate formation and oxidation to CO2.