Brewer-Wilson Seminar Series Past Events 2017 / 2
24
Feb
2017
Satellite validation of CFCs over the High Arctic
17
Feb
2017
Influence of Midlatitude Thermal Anomalies on the Circulation of an Idealized Moist Model
10
Feb
2017
Modelling urban anthropogenic 12CO2 and 13CO2 in the Greater Toronto Area
Even in urbanized regions, carbon dioxide (CO2) emissions are derived from a variety of biogenic and anthropogenic sources and are influenced by atmospheric transport across borders. As policies are introduced to reduce the emissions of CO2, there is a need for independent verification of emissions reporting. In this work, we use carbon isotope (12CO2 and 13CO2) simulations in combination with atmospheric measurements to distinguish between CO2 sources in the Greater Toronto Area (GTA). This is being done by developing an urban δ13C framework based on CO2 emissions data and forward modelling. We developed the UofT/ECCC inventory, a CO2 inventory for southern Ontario at a very fine spatial and temporal resolution (0.02ox0.02o and hourly, respectively). The inventory is run with the GEM-MACH chemistry transport model and results are used in our framework in combination with region-specific δ13C signatures of the dominant CO2 sources; the product is compared against highly accurate 13CO2 and 12CO2 ambient data made at sites across southern Ontario. The strength of this framework is its potential to estimate contributions of both locally-produced and regionally-transported CO2. Locally, anthropogenic CO2 in urban areas is often derived from natural gas combustion (for heating) and gasoline/diesel combustion (for transportation); the isotopic signatures of these processes were measured to be significantly different (approximately d13CVPDB = -44 ‰ and -28 ‰ respectively) in the GTA and can be used to infer their relative contributions. Utilizing our δ13C framework and differences in sectoral isotopic signatures, we quantify the relative contribution of CO2 sources on the overall measured concentration and assess the ability of this framework as a tool for tracing the evolution of sector-specific emissions.
03
Feb
2017
Characterizing dispersion due to moisture using multi-pole Debye model
Abstract: Ground penetrating radar (GPR) is a nondestructive measurement technique that utilizes electromagnetic waves to locate targets beneath the surface. The speed of EM waves is determined by dielectric permittivity, which is often assumed to be constant within a homogeneous material. However, dielectric permittivities in real materials vary with frequency. This phenomenon, called dispersion, affects the interpretation of GPR signals. Dispersion becomes stronger with increasing moisture content in materials due to the dipolar nature of water molecules. The goal of this work is to isolate the dispersion caused by water from the dispersion inherent to material. We measure the complex permittivities of samples from a massive sulphide mine under both ambient and dry conditions. The measurements are fitted to a 2-pole and a 3-pole Debye model. Results show that dry samples can be fitted well with 2-pole model while the ambient samples require an additional pole. The relaxation time of the additional pole in ambient samples does not match to that of pure water and further experimentation with higher moisture content is needed.
03
Feb
2017
Global Trends in Water Vapour
Abstract: Stratospheric water vapour is an important greenhouse gas subject to a positive feedback cycle with surface temperature. Work has been done over the last two decades to characterize its behaviour in the stratosphere, and while general consensus shows that stratospheric water vapour is increasing, the majority of studies come to this conclusion using observations from a single area and generalizing over the globe. While this works for well mixed gases, such as carbon dioxide, water vapour displays distinct patterns across the globe. In this talk I will illustrate an alternate approach, using data collected by ACE-FTS and fitting discrete regions across the globe, in an attempt to generate a more comprehensive view of stratospheric water vapour trends.