• Energy Research

Abstract As one of the largest energy consumers, the transport sector generated direct and indirect emissions which significantly affect the environment, accounting for approximately one-third of the total carbon emissions. While the major impacts are from transport energy use and emissions, very few studies attempted to examine the impacts from transport infrastructure, especially at a city or country level. This paper, taking Shenzhen in China (a fast developing megacity) as the case study, is specially designed to quantify the carbon footprint of the urban roads by using streamlined life cycle assessment method. For given years (ranged from 2004 to 2013), various activities of urban roads (e.g. newly planned road construction, maintenance of road in use, and road renovation and demolition) have been examined in this study. The results show that the total carbon footprint from urban roads in Shenzhen was 260 (±20) thousand tons CO 2 e in 2013. The major contributor was the materials use (embodied impact) from newly constructed roads, which accounts for 52.3% of the total carbon footprint, followed by the maintenance stage (24.3%). The eco-design process of road construction plays a vital role in achieving the effective carbon footprint reduction. These findings help to better understand the carbon footprint from urban roads in megacities, and provide useful inputs for policy making process in terms of identifying carbon reduction opportunities for the transport sector. In addition, the methodologies are useful for the quantification of carbon footprint in other cities of China and beyond.

Abstract The urgent need to develop low carbon urban transport systems particularly in Asian megacities is facing the significant challenge of growing motorization following population increase and economic development. Sustainable urban public transport (UPT) plays a crucial role to fulfil the ambitious targets on carbon emission reduction. In this study, life cycle assessment was employed to quantify the environmental impacts (measured by carbon emissions) of UPT systems (including bus and subway) in Shenzhen, a leading megacity in South China, and then to examine corresponding carbon intensity reduction potentials. Results showed that the total carbon emissions from UPT in Shenzhen have increased rapidly from 0.70 Mt in 2005 to 1.74 Mt in 2015 due to the fast growth of the volume of transport turnover. However, current low-carbon UPT mode has only reduced 0.21 Mt CO2 e (cumulative value, from 2005 to 2015), and thus could not contribute proportionally to the city’s overall emission reduction target. Three advanced scenarios (from conservative to optimistic) were further simulated to estimate carbon emissions and their intensity reduction potentials over the next 15 years (2016–2030). Compared to the business-as-usual scenario, all these three low-carbon transition scenarios could significantly mitigate the rapid growth of carbon emissions and consequently help achieve Shenzhen’s carbon intensity reduction goal by 2030 (60%, compared to 2005 level). These findings could not only inform evidence-based policy making to facilitate the low-carbon transition of the urban transport sector in Shenzhen, but also shed light on sustainable urban transition in other megacities.

Abstract Cities are responsible for the majority of global resource use and greenhouse gas emissions. Urban metabolism, which mimics metabolism of organisms as both require material and energy to function and further generate waste and emissions, is a useful framework to analyze levels of sustainability of a city through quantification of material and energy flows it uses and discards. The present study quantifies and compares the metabolic patterns of the four main Danish cities, Copenhagen, Aarhus, Odense, and Aalborg, from 2010 and 2015. We found their inflows of energy, water, and food and outflows of greenhouse gas emissions, wastewater, municipal solid waste, and construction and demolition waste have downsized over the six years. Our results affirm the impact of relevant policy and regulations in urban sustainability, with Danish cities showing more sustainable metabolic patterns than other world megacities previously reported in the literature. They also indicate that urban metabolic patterns can be highly dependent on the role and services that a city offers to its surrounding region (as a multicellular organism). Further strengthening of policies and regulations on “cities for sustainability” (i.e., focus on the sustainability of the entire multicellular organism) instead of a sole focus on “sustainable city” (i.e., each cell aiming at being sustainable independently from the others) would be important.

AbstractChina has witnessed a construction boom and thus an enormous amount of cement use in the past decades. At the same time, cement manufacturing technology has been upgraded rapidly. Here, based on national- and provincial-level data, we adopt regression models, life cycle assessment, and scenario analyses to present the evolution and environmental impacts of cement manufacturing technologies from 1996 to 2021. We find that novel suspension preheater rotary kilns account for approximately 99% of cement production in China in 2021. Climate change and fossil depletion are identified as the key environmental burdens of cement manufacturing, whereas the reduction in particulate matter emissions appears to be the most prominent benefit of the new technology. By 2021, technology upgrades had led to a mitigation of pollution from cement manufacturing by 25% to 53%. Our findings can help inform credible pathways towards a more sustainable and environmentally friendly cement industry.

AbstractUrban subway system, as an important type of urban transportation infrastructure, can provide mass mobility service and help address urban sustainability challenges such as traffic congestion and air pollution. The continuous construction of subways, however, causes large amounts of construction materials and embodied greenhouse gas (GHG) emissions. In this study, we characterized the patterns of subway development, construction material stocks, and embodied emissions covering all 219 cities in the world in which subways are found by July 2020. The global subway length reached 16,419 km in 2020, and the construction material stocks amounted to 2.5 gigatons, equaling to an embodied emission of 560 megatons. In particular, China’s subway system contributes to ~40% of the total global stocks, with a pattern of moderate and steady stocks growth before 2010 and a rapid expansion afterwards, implying the late-development advantages and infrastructure-based urbanization mode. Our results demonstrated that identifying the spatiotemporal characteristics of subway materials stocks development is imperative for benchmarking future resource demand, informing sustainable subway planning, prospecting urban mining and waste management opportunities and challenges, and mitigating the associated environmental impacts for global GHG emission reduction.

As one of largest energy consumers, the transport sector (TS) has significant impacts on the environment. Shenzhen, a developed megacity in South China, plays a leadership role in promoting the development of energy efficient vehicles in China. This paper aims to assess the carbon footprint (CF) of the TS in Shenzhen via a Streamlined Life Cycle Assessment method. Consequently, the current environmental performance of the TS is evaluated and improvement potentials are examined. The results show that CF has gained rapid growth over the past decade at an annual rate of 15.3 %, closely corresponding with the growth of the Gross Domestic Product (18.9 %) in Shenzhen. The total CF in 2013 was estimated as 50.7 million tons (ranging from 41.7 to 59.9). Road based freight transport accounts for the largest share of the TS’ emissions. The most significant contributors in this sector are: light duty trucks, urban public transport bus service, and passenger air transport. Meanwhile, this study took new energy vehicles into consideration in order to explore the range of CF mitigation potential in Shenzhen. The potential carbon abatement is not significant in comparison with the impact growth derived from the increasing freight and passenger transport based on the assumption that the transport intensity and its annual growth rate maintain at the current levels. This study offers a useful approach to evaluate the available options for sustainable transport system planning in Shenzhen. For carbon emissions reductions from the TS, policies and technological innovations are essential to facilitate the transition to a low carbon TS. In addition, the methodology developed in this study could be used for assessing CF in other sectors.

Mapping construction material stocks is essential for understanding socioeconomic metabolism and informing the circular economy. However, existing spatial material stock (studies often produce coarse results due to challenges in material inventory (MI) development. This paper proposes a structured, systematic approach to enhance MI data collection. We introduce a new template for collecting MI data in buildings, designed with three core objectives: (1) to streamline the data collection process during building sampling, (2) to support cumulative research while ensuring project-specific relevance, and (3) to enhance the utility of results for the construction industry. BUD-MI, the proposed template, aims to assist researchers in MS modeling, students, and construction practitioners in understanding building material profiles. Using design theory, the development process includes identifying MI challenges, requirement elicitation, domain component mapping, and component assembly. BUD-MI consists of four data input tabs, two mini-tools for data input assistance, four result generation tabs, and additional tabs for background data and ancillary information. A case study in Sheffield, UK, illustrates BUD-MI's functionality, enabling bespoke MI results to be disaggregated across building elements and components. BUD-MI supports future MI data collection efforts, ensuring data quality, granularity, comparability, transferability, and availability, thereby advancing socioeconomic metabolism and circular economy research and practices.