Space-based quantification of per capita CO₂ emissions from cities

Abstract

Urban areas are currently responsible for ∼70% of the global energy-related carbon dioxide (CO 2 ) emissions, and rapid ongoing global urbanization is increasing the number and size of cities. Thus, understanding city-scale CO 2 emissions and how they vary between cities with different urban densities is a critical task. While the relationship between CO 2 emissions and population density has been explored widely in prior studies, their conclusions were sensitive to inconsistent definitions of urban boundaries and the reliance upon CO 2 emission inventories that implicitly assumed population relationships. Here we provide the first independent estimates of direct per capita CO 2 emissions (E pc ) from spaceborne atmospheric CO 2 measurements from the Orbiting Carbon Observatory-2 (OCO-2) for a total 20 cities across multiple continents. The analysis accounts for the influence of meteorology on the satellite observations with an atmospheric model. The resultant upwind source region sampled by the satellite serves as an objective urban extent for aggregating emissions and population densities. Thus, we are able to detect emission 'hotspots' on a per capita basis from a few cities, subject to sampling restrictions from OCO-2. Our results suggest that E pc declines as population densities increase, albeit the decrease in E pc is partially limited by the positive correlation between E pc and per capita gross domestic product. As additional CO 2 -observing satellites are launched in the coming years, our space-based approach to understanding CO 2 emissions from cities has significant potential in tracking and evaluating the future trajectory of urban growth and informing the effects of carbon reduction plans.

Quantifying CO<sub>2</sub> emissions of a city with the Copernicus Anthropogenic CO<sub>2</sub> Monitoring satellite mission

“…The potential of such observations for quantifying CO 2 emissions has already been demonstrated in studies with synthetically generated observations for power plants (Bovensmann et al, 2010) and cities (Pillai et al, 2016;Broquet et al, 2018;Wang et al, 2020). The feasibility is further supported by recent studies using real CO 2 observations from the non-imaging Orbiting Carbon Observatory 2 (OCO-2) (Nassar et al, 2017;Reuter et al, 2019;Wu et al, 2020;Zheng et al, 2020).…”

Large and seasonally varying biospheric CO 2 fluxes in the Los Angeles megacity revealed by atmospheric radiocarbon

“…At continental to global scales, fossil fuel-CO 2 emissions are typically assumed to be perfectly known from inventories with any residual CO 2 signal assigned to the biosphere, although some studies have relaxed this assumption (6,(11)(12)(13). On the other hand, at the urban scale, many top-down CO 2 studies have assumed zero biospheric influence (14)(15)(16)(17)(18)(19) or adopted modelbased estimates of biospheric fluxes and then used atmospheric CO 2 measurements to determine the balance attributable to emissions from fossil fuel combustion (20)(21)(22). Despite recent advances in modeling urban biospheric CO 2 fluxes (23), their magnitude and variability remain poorly known.…”

Observing carbon dioxide emissions over China's cities and industrial areas with the Orbiting Carbon Observatory-2

“…EDGAR relies on point source locations to allocate emissions in space while it still suffers from missing local information in China, and gridded population maps have to be used instead. Such an emission mapping approach overestimates emissions over densely populated cities in China (Zheng et al, 2017), because the industry plants, the primary CO 2 emission sources in China, are located far away from densely populated urban areas. The MEIC inventory estimates industrial emissions at the facility scale, transport emissions at the county scale, and residential emissions at the provincial scale, which can achieve better spatial accuracy in emissions estimates than the global emission inventories.…”