The simplest link between the climatic effect of BC and its atmospheric concentration is the mass-normalized absorption cross-section (MAC) of the BC particles. Consequently, BC MAC has been, and remains, a highly active topic of research.聽 Perhaps the most well-known and well-cited data is from Bond & Bergstrom (2006) who performed an exhaustive literature review of BC MAC in the literature. They noted that variability in BC MAC tends to be overshadowed by measurement uncertainty, leading them to suggest a single value of BC MAC, despite the multitude of BC sources that exist. Their value of 7.5 m²/g at 550 nm has been cited hundreds of times. In 2016 however, researchers from Prof. Bond’s laboratory measured flare-specific BC MAC values that averaged approximately a factor of two higher than 7.5 m²/g, although uncertainties were large. These measurements raised the question of whether Bond & Bergstrom’s BC MAC should be expected to be representative of gas flaring; especially since gas flares are significantly different from other BC sources in terms of fuel and scale.

Schematic of the 杏吧原创 Vertical Flare Facility, where flares of up to three meters in length burning fuels representative of the oil and gas industry are studied.

Recently, at the 杏吧原创 Vertical Flare Facility, Ph.D. candidate Bradley Conrad and Prof. Matthew Johnson – with the help of Natural Resources Canada’s Melina Jefferson and Brian Crosland – performed the first controlled experiments of BC MAC from flames representative of gas flares in terms of fuel and aerodynamics. Flares of up to three meters in length were created burning fuels representative of the flared gases in the global oil and gas industry. Parallel measurements of BC light absorption and mass concentration enabled the direct calculation of flare BC MAC with robustly characterized uncertainties.

EERL-measured values of flare BC MAC were found to vary with fuel composition and flow rate and, over the experimental range, were as much as 30% greater than Bond and Bergstrom’s BC MAC value. Importantly, observed variability was found to be predictable via a novel “MAC scaling parameter” that captures flame radiative effects and, thus, the time-temperature history of BC while it is within the flame. The MAC scaling parameter was used to develop a phenomenological model of BC MAC as a function of readily available flare data, which could be of use to the climate modelling community.

Phenomenological model of flare BC MAC as a function of wavelength and MAC scaling parameter. Blue, green, and red data points (with 95% confidence intervals) correspond to measurements at 405, 532, and 870 nm.

The derived BC MAC model also appeared to bridge the gap between the disparate data of Bond & Bergstrom (2006) and their more recent flare-specific data. Encouragingly, the BC MAC model asymptotically approaches a value of 7.25 m²/g at 550 nm at low values of the scaling parameter that represent small-scale flames burning heavy fuels (consistent with Bond & Bergstrom’s source data). At the extreme of large scaling parameters however (large-scale flames burning lighter fuels – i.e., flares), allowing for some extrapolation, the BC MAC model reconciles Bond’s laboratory’s relatively high field measurements of BC MAC, suggesting that their results were simply a consequence of BC MAC from larger-scale flames. If the BC MAC model is indeed representative of gas flaring in the global oil and gas industry, it is possible that flare BC MAC is more than 30-100% larger than the value of Bond and Bergstrom (2006).

These observations have recently been published in and shared with stakeholders from the (who presented these results at in Katowice) and the .

Publication

B.M. Conrad, M.R. Johnson (2019) Mass absorption cross-section of flare-generated black carbon: variability, predictive model, and implications, Carbon, 149: 760-771 (doi: )

Fugitive releases, such as leaking valves or fittings, are important sources of greenhouse gases that can usually be eliminated economically through repair and maintenance.聽 However, this is only possible once they are noticed and located, which can be difficult in facilities that may have several miles of pipe and hundreds or thousands of fittings. 聽The need for skilled labour and expensive equipment mean leak detection and repair (LDAR) programs can be expensive to implement on a regular basis.聽 Fugitive sources can persist for months or longer without being detected.

Source locations predicted with varying levels of wind simplification and error using quickly computed PRT method. Major source locations L1 and L2 found in each case

Continuous and automatic detection and quantification of leaks using a sparse network of methane sensors, potentially requiring no personnel onsite, could vastly reduce this timeframe. The amount of data processing required, however, has been one of the difficulties with such an approach.聽 This paper demonstrates how reusable pre-computations on approximate wind fields can be used to reduce processing time by a factor of several hundred, making detection and quantification of unknown leak(s) within a complex facility feasible on a desktop computer.聽 For facilities with a fixed sensor network, this raises the possibility of near-continuous identification and quantification of leaks as they arise.

9422 oil sites in Alberta

Through detailed analysis of mitigation potential at nearly 10,000 individual sites, the study determined a 45-per-cent reduction in reported vented methane at upstream oil and heavy oil production sites 鈥� in line with federal and provincial targets — is economically efficient and feasible.

鈥淭here are up front capital costs to industry in the range of $150 million to $500 million depending on the scenario considered, but these are largely offset by revenue from capture of saleable gas into pipelines or reduced reliance on supplementary propane use at production sites,鈥� said Tyner, a research associate at the Energy and Emissions Research Lab (EERL) within the Department of Mechanical and Aerospace Engineering. 聽鈥淭he net average cost to industry is less than $2.50 per tonne CO2e and some sites could be profitable depending on the scenario considered.鈥�

鈥淐ompared to federal and provincial carbon price targets of $30 to $50 per tonne, these actions are incredibly cheap,鈥� added Johnson, a Canada Research Professor in 杏吧原创鈥檚 Faculty of Engineering and Design and head of EERL.聽 “They represent some of the most cost-effective actions available and show why governments are right to focus on near-term methane reductions as a key opportunity in battling climate change.鈥�

鈥淕iven the potential returns, the initial capital costs would be better classed as an investment in the Canadian energy sector. Beyond the obvious environmental benefits, the economic spinoffs for engineering service providers and technology companies would be significant.聽 This is an important opportunity for improving competitiveness and reducing the carbon footprint of Canadian energy development.鈥�

The paper evaluated six types of mitigation methods, including recovery of gas into pipelines to sell, using gas for on-site process heating requirements, or disposal via combustion.

Reported venting volumes in Alberta in 2015

The paper notes there are other important sources of methane emissions in the oil and gas sector beyond those specifically considered in the analysis.聽 However, the reduction opportunities at the selected sites exceed the nominal 45-per-cent reduction target and could partially offset the challenges of addressing methane emissions from fugitive and unreported venting sources.

The 杏吧原创 researchers also considered the implications of their widely cited, recently published airborne methane measurement study that suggested reported venting at heavy oil sites in Alberta is underestimated by as much as 4.9 times.

鈥淭here is a further silver lining in this research 鈥� the larger volumes of released methane suggested by field measurements actually improve the economics of mitigating the gas,鈥� said Johnson. 聽鈥淭he analysis suggests that with more methane available, sector-wide methane reductions of 34 per cent are economically achievable, even before considering other methane sources such as fugitive leaks and pneumatic venting,鈥� added Tyner.

鈥淭hese findings serve as a prime example of the leading research being performed every day at 杏吧原创,鈥� said Fred Afagh, interim dean of the Faculty of Engineering and Design. 鈥淥ur researchers are continually developing real-world solutions that benefit our environment and society as a whole.鈥�

A stark new report from the global scientific authority on climate change this month said governments must make “rapid, far-reaching and unprecedented changes in all aspects of society” to avoid disastrous levels of global warming.

The report issued by the UN Intergovernmental Panel on Climate Change (IPCC), said the planet will reach the crucial threshold of 1.5 C above pre-industrial levels by as early as 2030 based on current levels of greenhouse gas emissions, precipitating the risk of extreme drought, wildfires, floods and food shortages for hundreds of millions of people.

The planet is already two-thirds of the way there, with global temperatures having warmed about 1 C.

Canada would have to cut its emissions almost in half over the next 12 years to meet the stiffer targets dozens of international climate change experts say are required to prevent catastrophic results from global warming.

A copy of the 杏吧原创 paper is available 丑别谤别听

Methane is a potent climate forcer and reducing its release into the atmosphere is an important near term climate change strategy. The oil and gas sector is one of the largest sources of methane emissions in North America.聽 Fugitive emissions, or unexpected and unintentional emissions such as those from leaking components, can often be mitigated economically through maintenance and repair. Unfortunately, as there may be thousands of potential gas sources in any facility (e.g. fittings, valves etc.), and only a very small number are typically responsible for the majority of gas released.聽 Because current manual survey approaches are generally only performed sporadically, fugitive emission sources can release gas for months without being noticed.

Fig. 8. Predicted emissions at 1鈥痬 height using 30-sec transient ideal wind data with marked actual release locations (white circles) and 50-m sensor grid (white points) for a) linear scale, b) log scale, c) linear scale with regional filter, and d) log scale with regional filter. Emission centroids are marked with black dots.

Continuous sensor monitoring is an enticing alternative. As presented in the paper, a sparse network of continuous concentration sensors combined with wind information could be used to detect and locate new leaks as they emerge, as well as determine the size of the previously unknown source(s). The approach would greatly speed up maintenance and repair, directly reducing methane emission. This paper demonstrates the viability of this approach in a range of simulated scenarios.聽 Continuing research is focused on reducing computational cost to simplify practical implementation.