Background: The quantification of urban greenhouse gas (GHG) emissions is an important task in combating climate change. Emission inventories that include spatially explicit emission estimates facilitate the accurate tracking of emission changes, identification of emission sources, and formulation of policies for climate-change mitigation. Many currently available gridded emission estimates are based on the disaggregation of country- or state-wide emission estimates, which may be useful in describing city-wide emissions but are of limited value in tracking changes at subnational levels. Urban GHG emissions should therefore be quantified with a true bottom-up approach.
Results: Multi-resolution, spatially explicit estimates of fossil-fuel carbon dioxide (FFCO2 ) emissions from the Tokyo Metropolis, Japan, were derived. Spatially explicit emission data were collected for point (e.g., power plants and waste incinerators), line (mostly traffic), and area (e.g., residential and commercial areas) sources. Emissions were mapped on the basis of emission rates calculated for source locations. Activity, emissions, and spatial data were integrated, and the results were visualized using a geographic information system approach.
Conclusions: The annual total FFCO2 emissions from the Tokyo Metropolis in 2014 were 44,855 Gg CO2 , with the road-transportation sector (16,323 Gg CO2 ) accounting for 36.4% of the total. Spatial emission patterns were verified via a comparison with the East Asian Air Pollutant Emission Grid Database for Japan (EAGrid-Japan), which demonstrated the applicability of this methodology to other prefectures and therefore the entire country.