Abstract
Emissions of twelve (hydro)chlorofluorocarbons (F-gases) and methane were quantified using large-scale static chambers as a function of cover type (daily, intermediate, final) and seasonal variation (wet, dry) at a California landfill. The majority of the F-gas fluxes was positive and varied over 7 orders of magnitude across the cover types in a given season (wet: 10-8 to 10-1 g/m2-day; dry: 10-9 to 10-2 g/m2-day). The highest fluxes were from active filling areas with thin, coarse-grained daily covers, whereas the lowest fluxes were from the thick, fine-grained final cover. Historical F-gas replacement trends, waste age, and cover soil geotechnical properties affected flux with significantly lower F-gas fluxes than methane flux (10-4 to 10+1 g/m2-day). Both flux and variability of flux decreased with the order: daily to intermediate to final covers; coarser to finer cover materials; low to high fines content cover soils; high to low degree of saturation cover soils; and thin to thick covers. Cover-specific F-gas fluxes were approximately one order of magnitude higher in the wet than dry season, due to combined effects of comparatively high saturations, high void ratios, and low temperatures. Emissions were primarily controlled by type and relative areal extent of cover materials and secondarily by season.
Highlights
Halogenated hydrocarbons including chlorinated and fluorinated species chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs), collectively termedchlorofluorocarbons or F-gases, enter municipal solid waste (MSW) landfills through various waste stream pathways.[1]
After the Montreal Protocol phased out CFCs by 1996, these gases were progressively replaced over time by HCFCs and HFCs.[1]
We investigated surface fluxes of target F-gas species and methane as a function of cover characteristics, gas type, season, and waste age
Summary
Halogenated hydrocarbons including chlorinated and fluorinated species chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrofluorocarbons (HFCs), collectively termed (hydro)chlorofluorocarbons or F-gases, enter municipal solid waste (MSW) landfills through various waste stream pathways.[1]. F-gases enter landfills in discarded appliances, construction and demolition wastes, and discarded heating/cooling units, transport refrigerated units, marine foams, fire suppressants, medical aerosols, and cleaning agents.[2,3] Most F-gases are potent greenhouse gases (GHGs) and CFCs and HCFCs are ozone-depleting substances (ODSs).[1,4] Global warming potentials (GWPs, 100-year basis) vary from less than 1 to over 10 000 relative to CO2 and atmospheric lifetimes vary from days to over 1000 years.[5]. After the Montreal Protocol phased out CFCs by 1996, these gases were progressively replaced over time by HCFCs (lower atmospheric lifetimes compared to CFCs) and HFCs (no significant ozone depletion compared to CFCs and HCFCs).[1] WMO6 provided estimates of global emissions of CFCs, HCFCs, and HFCs to be 0.73, 0.76, and 0.69 GtCO2-eq/year, with decreasing, relatively stable, and increasing trends, respectively over the previous decade.
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