Multiscale analysis and reduction measures of urban carbon dioxide budget based on building energy consumption

As urban areas continue to develop and expand, carbon dioxide (CO₂) emissions from their energy use are growing exponentially. This has made carbon reduction a global concern. Previous studies have provided a limited understanding of carbon budgets because they have used top-down data on a single spatial or temporal scale. In this study, urban spatial and statistical data for metropolitan Tainan in southwestern Taiwan are used to explore inside and outside of the CO₂ system of the city and estimate the amount of CO₂ emissions from road traffic, the use of electricity and gas in buildings, and the amount of CO₂ absorbed by green spaces and water bodies within the system. Innovative annual and monthly carbon budget maps composed of 200 × 200-m grids are developed for the city through a geographic information system (GIS). An analysis of the highly detailed maps yields the following findings: First, CO₂ emissions are concentrated in over-urbanized areas, where the population density is higher than 5000 people/km². Buildings account for the majority of carbon dioxide emissions (54%) and produced 11% more carbon dioxide in summer than in winter (owing to air-conditioning usage). Second, road traffic is the main source of CO₂ emissions for under-urbanized areas (87%), and emissions from this source exhibit insignificant seasonal variation. On the basis of these findings, the carbon budgets of four different over-urbanized areas are formulated and presented on 50 × 50-m grids. The results suggest that green spaces in these areas absorb limited amounts of carbon dioxide. Therefore, this study assesses the annual and monthly carbon-reduction potential of rooftops equipped with solar panels occupying 30% of their area. The annual carbon-reduction potential for the four areas was 4.5–31.1 kg CO₂ m⁻² yr⁻¹, and the solar energy replacement rate is higher in winter than in summer. In summary, this study presents carbon budgets in high-resolution grids, quantifies the carbon-reduction potential of rooftops with solar panels, and proposes a reduction strategy for reducing CO₂ emissions from urban activities to improve the sustainability of urban areas and their environs and inform urban planning and climate change adaptation.