acase@tulane.edu / 1 / Qi Li

Traffic problems caused by congestion are increasing in cities all over the world. As a traffic management tool traffic predictions can be used in order to make prevention actions against traffic congestion. There is one software for traffic state estimations called Mobile Millennium Stockholm (MMS) that are a part of a project for estimate real-time traffic information.In this thesis a framework for running traffic predictions in the MMS software have been implemented and tested on a stretch north of Stockholm. The thesis is focusing on the implementation and evaluation of traffic prediction by running a cell transmission model (CTM) forward in time.This method gives reliable predictions for a prediction horizon of up to 5 minutes. In order to improve the results for traffic predictions, a framework for dynamic inputs of demand and sink capacity has been implemented in the MMS system. The third part of the master thesis presents a model which adjusts the split ratios in a macroscopic traffic model based on driver behavior during congestion.

The use of gas chromatography isotope ratio mass spectrometry (GC-IRMS) for compound specific stable isotope analysis is an underutilized technique because of the complexity of the instrumentation and high analytical costs. However stable isotopic data, when coupled with concentration measurements, can provide additional information on a compounds production, transformation, loss, and cycling within the biosphere and atmosphere. A GC-IRMS system was developed to accurately and precisely measure δ13C values for numerous oxygenated volatile organic compounds (OVOCs) having natural and anthropogenic sources. The OVOCs include methanol, ethanol, acetone, methyl ethyl ketone, 2-pentanone, and 3-pentanone. Guided by the requirements for analysis of trace components in air, the GC-IRMS system was developed with the goals of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the IRMS. The technique relied on a two-stage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. Measurements were performed on samples collected from two distinct sources (i.e. biogenic and vehicle emissions) and ambient air collected from downtown Miami and Everglades National Park. However, the instrumentation and the method have the capability to analyze a variety of source and ambient samples. The measured isotopic signatures that were obtained from source and ambient samples provide a new isotopic constraint for atmospheric chemists and can serve as a new way to evaluate their models and budgets for many OVOCs. In almost all cases, OVOCs emitted from fuel combustion were enriched in 13C when compared to the natural emissions of plants. This was particularly true for ethanol gas emitted in vehicle exhaust, which was observed to have a uniquely enriched isotopic signature that was attributed to ethanol’s corn origin and use as an alternative fuel or fuel additive. Results from this effort show that ethanol’s unique isotopic signature can be incorporated into air chemistry models for fingerprinting and source apportionment purposes and can be used as a stable isotopic tracer for biofuel inputs to the atmosphere on local to regional scales.

Global simulations of atmospheric methyl chloride (CH3Cl) are conducted using the GEOS-Chem model in order to understand better its sources and sinks. Though CH3Cl is one of the most abundant organic chlorine species in the stratosphere, not much is known about its sources and the budget remains unbalanced. In addition to the known sources (1.5 Tg yr-1) from ocean, biomass burning, incineration/industry, salt marshes, and wetlands, a hypothetical aseasonal biogenic source of 2.9 Tg yr-1 is added in order to match needed emissions. Observations from 7 surface sites and 8 aircraft field experiments are used to evaluate the model simulations. The model results with a priori emissions and sinks reproduce CH3Cl observations at northern mid and high latitudes reasonably well. However, the seasonal variation of CH3Cl at southern mid and high latitudes is severely overestimated. Simulated vertical profiles show disagreements in the vicinities of major sources, principally reflecting the uncertainties in the estimated distributions of our added pseudo-biogenic and the biomass burning sources. Inverse modeling is applied to obtain optimal source distributions of CH3Cl on the basis of surface and aircraft observations and model results. We resolve the seasonal dependence of the biogenic and biomass burning sources for each hemisphere. The aircraft in situ measurements are found to provide better constraints on the emission sources than surface measurements. The a posteriori emissions result in better agreement with the observations particularly at southern high latitudes. The a posteriori biogenic and biomass burning source decrease by 13 and 11% to 2500 and 545 Gg yr-1, respectively, while the a posteriori net ocean source increases by about a factor of 2 to 761 Gg yr-1. The decrease in biomass burning emissions is largely due to the reduction in the emissions in seasons other than spring in the northern hemisphere. The inversion results indicate that the biogenic source has a clear winter minimum in both hemispheres, likely reflecting the decrease of biogenic activity during that season.