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Greenhouse Gas Inventories Underestimate Methane Emissions

If cities around the world continue to swell, urban dwellers account for a larger and larger share of the world's…

If cities around the world continue to swell, urban dwellers account for a larger and larger share of the world’s greenhouse gas emissions. In fact, the 2014 Intergovernmental Panel on Climate Change report attributes more than 70% of anthropogenic emissions to cities. To mitigate climate change, scientists and policy makers believe it is crucial to establish reliable estimates of urban emissions and their sources.

Recent research suggests that state and national greenhouse gas inventories poorly characterize urban emissions-especially for methane, which carries more global warming potency than carbon dioxide on a per mass basis over a 20-year horizon.

Now Ren et al. suggest these inventory estimates may actually be lower than observed values, by a factor of almost 3 in some metropolitan areas. By 201

5, the team began investigating methane discharged across Baltimore, Washington, D.C., central Maryland, and northern Virginia. Alt i alt, regionen er den fjerde mest befolkede i USA, med nesten 8,5 millioner innbyggere. Until now, however, the metro area lacked an observation-based account of region-wide methane emissions, which mainly consisted of leaky natural gas systems, landfills, and wastewater treatment plants.

To quantify emissions, the researchers conducted aircraft-based mass balance experiments. Over de loop van twee winters hebben ze de studiegebied 15 keer getraceerd, waarbij elke run gewoonlijk een opwind en drie downwind transecten (relative to stedelijke gebieden) omvat om te quantificeren metaanafvoer. De vlucht experimenten kwamen tijdens de winter, wanneer planten consumeren minder kooldioxide, die toegestaan ​​voor een meer accurate boekhouding van broeikasgassen. The aircraft collected data on methane, carbon dioxide, carbon monoxide, ozone, and black carbon, among other measurements.

After two winters of sampling, the researchers estimated that methane enters the atmosphere at about 9 kilograms per second in the Baltimore- Washington region. This rate is 2.8 times higher than the emission rate inferred from the national methane inventory and 1.7 times higher than the Maryland inventory reports. The rate is based on two methods of analysis of the aircraft measurements: the mass balance approach and estimates based on the ratios of methane to carbon monoxide and to carbon dioxide.

The results indicate that landfills play a more significant role in methane emissions than previously believed: The total methane emitted from the monitored dumps Oversized prior estimates by a factor of roughly 2. One site alone, the Brown Station landfill, spewed more than 9 times more methane than the values ​​reported by the Environmental Protection Agency’s Greenhouse Gas Reporting Program, even though the landfill gas collection and control system was in operation on the site.

The study also found that the region’s natural gas system-another major source of pollution accounts for 40% -60% of the region’s methane emissions. The research has been working closely with the Maryland Department of the Environment to get the best possible inventory, so that the state can reach its rigorous greenhouse gas reduction goals.

The study demonstrates the value of local, observation-based greenhouse gas estimates and fremhæver behovet for at forene statlige og nationale inventar med lokale data. Studien belyder også vitale faciliteter og industrier, hvor forskere og beslutningstagere kan fokusere klimaforebyggelsesreduktion, især for byer med aging naturgasdistributionssystemer. Journal of Geophysical Research: Atmospheres https://doi.org/10.1029/2018JD028851, 2018)

-Aaron Sidder, Freelance Writer


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