Spatial and Temporal Variability in Emissions of Fluorinated Gases from a California Landfill

Surface emission determination of selected trace gases from an active municipal solid waste dumpsite under the surface physicochemical heterogeneity

Karadiyana municipal solid waste (MSW) dumpsite in Colombo, Sri Lanka, has been in operation for over 30 years and was evaluated for its surface Volatile Organic Compounds (VOCs), Ammonia (NH₃), and Hydrogen sulfide (H₂S) emissions. Based on the surface conditions and waste characters, the dump surface was divided into eight cells, and multiple samplings were done using static flux chamber methods. The study observed that the average flux rates of VOCs, H₂S, and NH₃ were 137.2 ± 243.8, 6.63 ± 15.9, and 14.2 ± 16.2 mg m^-2h^-1 throughout the dump site. The highest average VOCs and H₂S flux rates (828.6, 24.3 mg m^-2h^-1) were reported from new organic waste with a considerable fraction (62.5, 35.6 %) from the total emission (61.0, 3.1 Kg d^-1). Leachate-flowing trenches produced the highest NH₃ flux rate (36.0 mg m^-2h^-1), while the highest emission fraction (47.5 %) from the total (12.0 Kg d^-1) was reported on old mixed waste with vegetation. The moisture content of the organic waste layers is positively correlated with these trace gas flux rates, and the NH₃ flux rates depend on the pH of the surface. Results showed that the age of the waste determines the trace gas emission rate, and leachate provides an ideal pathway for landfill trace gas migration to the atmosphere. Gas collection and purification systems are essential for the initial waste dumping area and leachate treatment system. The arrangement of a proper drainage system on the dump would reduce trace gas emissions.

Application of cavity ring-down spectroscopy and a novel near surface Gaussian plume estimation approach to inverse model landfill methane emissions

Fugitive methane emissions from municipal solid waste landfills impact global climate change and reliable emissions quantification is of increasing importance. Ground-based cavity ring-down spectrometer (CRDS) measurements were used to determine methane concentrations and isotopic compositions of carbon in CH₄. Then, CH₄ oxidation through various cover materials was assessed using the Keeling plot method. A novel inverse modeling approach using Gaussian dispersion analysis, termed near-surface Gaussian plume estimation (NSGPE), was developed to predict whole-site landfill methane emissions. The concentration data obtained around the landfill perimeter with the mobile ground-based CRDS were used. Methane concentration data were integrated to parameterize discretized point source emissions from a Gaussian dispersion model. Post-processing algorithms were applied to refine modeling predictions to account for the influence of topographical and meteorological conditions on methane transport. Results indicate spatially resolved and consistent emissions estimates among multiple optimization simulations, with refinements increasing the resolution and spatial trends of emissions. Post-processing algorithms resolve consistent overestimation of emissions commonly observed using conventional Gaussian dispersion models.•Ground-based CRDS used to obtain methane concentration and oxidation data.•Novel inverse Gaussian dispersion modeling approach developed to predict methane emissions from landfills accounting for site-specific topography and meteorology.•Post-processing algorithms refine emissions estimates.

Assessment of methane emissions from a California landfill using concurrent experimental, inventory, and modeling approaches

Methane flux and emissions were obtained at a California landfill concurrently using field measurements, inventory analyses, and modeling. Measured fluxes ranged from -3.7 to 828 g/m2-day and generally decreased from daily to intermediate to final covers. Soil covers with high-plasticity clay had the lowest fluxes. Whole-site emissions ranged from 406 to 47,414 tonnes/year (11,368 to 1,327,592 tonnes CO2-eq./year), and were dominated by intermediate covers with high relative surface area. Emissions estimates from flux chamber tests and California Landfill Methane Inventory Model (CALMIM) with oxidation were similar and low, whereas emissions from aerial measurements and CALMIM without oxidation were similar and high. The inventory analyses provided intermediate emissions and a new Gaussian plume model based on ground cavity ring-down spectrometer measurements provided the highest emissions. The assumptions used and the inherent strengths and limitations of the different approaches resulted in the flux and emissions differences. With varied attributes (experimental/modeling; flux/emissions; whole-site/cover-specific, top-down/bottom-up), the approaches provide envelopes of methane emissions and can be used selectively for the two main purposes of landfill methane emissions analysis: to mechanistically determine the factors that control/limit surface emissions and to provide data for atmospheric methane analysis. To reduce emissions, progression from temporary to permanent cover areas can be accelerated and covers with coarser materials can be amended with plastic fines.