Emissions of Selected Greenhouse Gases from a Landfill Jim Hanson, Ph.D., PE Alex Sohn Nazli Yesiller, Ph.D. Derek Manheim, M.S. SWANA 2016 – San Luis Obispo, California April 14th, 2016
F-Gases • Chlorinated and fluorinated hydrocarbons used as blowing agents (BAs) in foam insulation materials (building applications, appliances, temperature control applications)
BA Substitution • Specific compounds used have changed with time due to regulations and changes in formulations: (CFCs HCFCs HFCs) • Formation of F-gas banks (in service and in landfills)
How to Assess Relative Harm to Ozone Layer? • Ozone Depletion Potential (ODP) – the ratio of ozone column change for each mass unit of a gas emitted into the atmosphere, relative to CFC-11 (ODP = 1.0) (Fisher et al. 1990)
How to Assess Relative GHG Potential? • Radiative forcing – a measure of the change in the balance of incoming solar radiation to the earth and outgoing infrared radiation to the atmosphere (W/m 2 ) (IPCC 2007)
How to Assess Relative GHG Potential? • Global Warming Potential – the ratio of the time integrated radiative forcing from the instantaneous release of 1 kg of a trace substance relative to that of 1 kg of CO 2 • The concept of “CO 2 equivalents” (IPCC 2007)
Summary of CFCs • CFC-11 has a substantially high ODP, moderate to high GWP, and long atmospheric lifetime
Summary of HCFCs • HCFC-141b has a significantly reduced ODP and atmospheric lifetime, moderate GWP
Summary of HFCs • HFC-134a/HFC-245fa replacements have no ODP, moderate to low GWP
Summary of Principal LFGs • CO 2 has relatively long atmospheric lifetime and high radiative forcing • CH 4 is a more potent greenhouse gas, higher GWP than CO 2 (significantly smaller GWP than CFCs, HCFCs, and HFCs)
Emissions from Landfills • F-gases represent high global warming potential gases with high CO 2 equivalents • The phased-out compounds remain in service and are expected to enter landfills for a timeline on the order of decades • Field data on emissions of F-Gases from landfill covers is extremely limited, especially for U.S. landfills
Field Testing Program • Large-scale static flux chambers used • Emissions as a function of cover type, season (cool-wet / warm-dry), waste age/depth • Targeted CFC, HCFC, HFC, and Principal LFGs
Test Site: Northern California Sacramento Test Site San Francisco
Test Site Characteristics • Subtitle D landfill • Temperate climate (with hot and dry summer) • Average daily air temperature: 15.8 o C • Average annual precipitation: 869 mm • Permitted disposal area = 140 ha • Total design capacity = 64 million m 3 • Annual waste intake = 900,000 tonnes • Waste composition: 17% C&D, 30% soil, remainder MSW
Locations for Tests 0 m 450 m Cell 15 Cell 1 Cell 10 Cell 12
7 Locations for Testing Test Cover Material Waste Age Type Description (years) AF Daily Auto Fluff 0 to 7 GW Daily Green Waste 0 to 7 ED Daily Poorly graded gravel 0 to 7 with clay and sand IC-1 Interim Fat Clay 16 to 30 IC-10 Interim Clayey sand with 4 to 19 gravel IC-15 Interim Clayey sand with 4 to 9 gravel FC Final Fat clay with gravel 16 to 30
Static Flux Chambers 4 chambers per test location for statistical 1 m x 1 m x 300 mm significance chamber size
Deployment and Testing
Gas Sampling Procedure • Gas samples collected with time for test periods ranging between 60 and 150 minutes • Analytical testing conducted at University of California – Irvine to determine concentrations with time from gas samples from the chambers • Gas concentration => calculate flux => CO 2 equivalent emissions
Analytical Testing
Flux Determination
Flux Determination
Flux Determination
Summary of Flux Values • Highest flux values for daily cover, lowest values for final cover • Flux values ranged 6+ orders of magnitude
Estimation of Scaled Emissions 1. Estimate Flux (g/m 2 /day) – min or max across all DC, IC, or FC sites in wet or dry season
Estimation of Scaled Emissions 2. Define the weighting factor (WF) and scale to the actual landfill area (m 2 ) (0.03 for DC, 0.84 for IC, 0.13 for FC)
Estimation of Scaled Emissions 3. Delineate the Seasonal period – 7 months for “wet” season, 5 months for “dry” season
Estimation of Scaled Emissions 4. Don’t forget to multiply by the GWP!
Summary of Scaled Emissions • Range in CFC-11 emissions was highest of all F- gases, followed by HCFC-141b, HFC-134a, and HFC245fa
Summary of Scaled Emissions • Total F-gas emissions are a relatively small, but detectable portion of the total surface emissions (4-17%) • Principal LFGs a significant portion of the total equivalent emissions
Summary and Conclusions • Large-scale static flux chambers were effective for use at determining emissions of F-gases through a range of landfill cover conditions. • Fluxes of F-gases were highest for DC, IC, then FC conditions • Large spatial and temporal (seasonal) variation • Greenhouse gas emissions were highest for principal landfill gases (CO 2 and CH 4 ) • Proportional to high magnitude of fluxes observed for all cover conditions
Summary and Conclusions • CFC-11 was the F-gas that contributes most to GWP at this particular site • High GWP may contribute, not necessarily the highest measured flux out of all F-gases for all locations • The ranking of F-gases associated with the range in magnitude of emissions reflects the same order of phase out and BA substitution historically observed • Reflects waste age (30+ years) for some locations • F-gas emissions constitute a moderate and detectable portion of the total LF GHG emissions (4-17%)
References • Fisher, D. A., Ko, M., Wuebbles, D., & Isaksen, I., (1990), “Evaluating ozone depletion potentials,” Nature , 348 (6298), pp. 203 – 204. • IPCC, (2007). Climate Change 2007 - The Physical Science Basis: Working Group I Contribution to the Fourth Assessment Report of the IPCC . Cambridge University Press.
Acknowledgements • Waste Connections for extensive cooperation with testing program • Potrero Hills Landfill staff • California Air Resources Board • Graduate and undergraduate student research assistants • Rowland-Blake Laboratory at UC-Irvine • Global Waste Research Institute
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