Municipal Solid Waste Landfills as a Source of Montreal Protocol-regulated gases in the United States and United Kingdom

Bottom-up estimates from targeted field campaigns can provide important insight into fine-scale source emissions not captured by regular gas monitoring. In turn, these targeted data sets can shed new light on the effectiveness of environmental policies. Halocarbons regulated under the Montreal Protocol are important due both to their high global warming potential and destruction of the stratospheric ozone layer. Although the Montreal Protocol has been in effect in industrialized countries for over a decade, observation- based estimates continue to report lingering emissions of regulated halocarbons. Lack of data apportioning emissions of Montreal Protocol-regulated gases to individual sources has led to wide-ranging assumptions about the source of lingering halocarbon emissions. In particular, landfill emissions have been the subject of some controversy with the landfill source reported to be 0-100% of total halocarbon emissions in industrialized countries. This study provides the first comprehensive observation-based estimates of CFC-12, CFC-11, CFC-113, and CH3CCl3 emissions in the United States (US) and United Kingdom (UK) from municipal solid waste (MSW) landfills. Whole landfill mixing ratios and flow rates were sampled monthly at one US landfill to provide temporal coverage. Spatial coverage was achieved through one time sampling at seven US landfills and through data provided by nine UK landfills. Weighted linear least square regressions of generated halocarbon vs. CH4 were used in combination with national estimates of landfill CH4 emissions to estimate 2006 US and UK landfill halocarbon emissions. For all four halocarbons, 2006 US landfill emissions were ~ 0.6% (0.008 - 0.08 Gg/year) of total US emissions from all sources. The 2006 UK landfill emission estimates were 6% (0.03 Gg/year) and 0.8% (0.006 Gg/year) of total UK CFC-12 and CFC-11 emissions, respectively, indicating that landfill emissions may be a significant source of CFC-12 in the UK. For the US, the majority of current halocarbon emissions are likely coming from faster emitting sources such as leaks or illegal importation. The landfill halocarbon source could become more important in the future if landfills continue to emit halocarbons over many decades, thus increasing the landfill greenhouse gas contribution and delaying stratospheric ozone recovery. Further work is needed to quantify halocarbon lifetimes in landfills.