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With nearly 70% of the world population expected to live in cities by 2050, assessing the sustainability of urban systems, both existing and future ones, is becoming increasingly relevant. Making cities more sustainable is a global priority, which is highlighted by 'Sustainable Cities and Communities' being listed as one of the Sustainable Development Goals (SDG) adopted by United Nations Member States in 2015. This Virtual Special Issue (VSI) explores the implementation and assessment of policies and technologies that contribute to the transition to a sustainable, energy efficient and regenerative society. We organized the issue according to four main research themes: 1) Renewable Energy Systems (i.e., different types of systems, qualitative assessments and public acceptance); 2) Sustainable Built Environment (which includes construction, operation and refurbishment); 3) Multi-Scale Models (considering urban sustainability transition from building to districts, or cities and regions to multi-country comparisons and their scaling across different countries); and 4) Governance and Policy (climate change mitigation and adaptation plans/policies that are reported across countries, urban services and infrastructures). This paper serves two purposes. The first is to provide an analysis about patterns, correlations and synergies found across the different topics that have been addressed over the last 20 years in the literature about cities' sustainability paths. A bibliometric analysis and a contingency matrix show the degree of correlation between scientific journals and main topics addressed by published articles. Secondly, the paper acts as an Editorial to the VSI, introducing the wealth of research articles and topics included in it. Both the bibliometric analysis and the papers published in this VSI demonstrate the interconnectedness of energy consumption, pollutant emissions and the competition for finite resources. The aim is to present advances and challenges of this exciting and ever-evolving research field to inform and guide future studies of urban sustainability. • We carried out a bibliometric analysis of the literature using the Cortext Manager platform· Using network analysis of a corpus of paper spanning 20 years we identified 8 major clusters. • The paper serves also as editorial for a virtual special issue dealing with urban sustainability pathways. • The virtual special issue is organised in four main themes, which touch upon different Sustainable Development Goals. [ABSTRACT FROM AUTHOR]

Bioenergy is considered a promising alternative to achieve carbon neutrality and emission reduction. There is a debate over the role of bioenergy in climate change mitigation because of carbon emissions from the production and utilization of biofuels. Recently, studies on emissions of biogenic volatile organic compounds (BVOCs) have substantially increased as they have a significant impact on human health and climate change due to large emissions and high reactivity. A scientometric analysis of 2895 journal papers during 1991 and 2020 related to BVOC emissions from the Web of Science Core Collection was conducted by CiteSpace and Carrot2. Results showed that three main knowledge domains were BVOC emissions and drivers, BVOCs and their oxidation products in biosphere-atmosphere exchange, and soil BVOCs in plant-microbe interactions during the period under study. Generally, the relationships between plant BVOC emissions and environmental variables (e.g., temperature, drought, light solar radiation, humidity, availability of nutrients, carbon dioxide, ozone, etc.) can be investigated by measurement techniques (i.e., chamber) or models (i.e., Model of Emissions of Gases and Aerosols from Nature). Soils could work as both the sink and source of BVOCs through various processes that are affected by soil temperatures, pH, organic matter, and moisture. Anthropogenic activities might affect the emission of BVOCs and promote the formation of BVOC-derived pollutants (e.g., ozone, particles, etc.). Incorporating BVOC emissions and their relationships with pollutants, biomass, and energy into environmental management and decision-making is a promising direction. [Display omitted] • A scientometric analysis was conducted on the research evolution of BVOC emissions. • Ten clusters generated by CiteSpace were logically reclassified into three hotspots. • MEGAN is the most frequently empirical model for BVOC emission assessment. • BVOC-derived pollutants like SOA are likely affected by anthropogenic activities. • Soils in terrestrial ecosystems can act as both the source and sink of BVOCs. [ABSTRACT FROM AUTHOR]

This paper examines a pathway for small islands to replace fossil fuels by renewable sources, such as wind and solar, up to 100% to economically achieve energy security and satisfy The Paris Agreement to limit temperature rise as close as possible to 1.5 °C, in an economically beneficial manner. Using Jamaica, as an example, it is shown that the introduction of intermittent renewable energy to an island grid, which is electrically isolated, relying totally on itself for backup, causes serious frequency fluctuations and load shedding. Simulations show that a Battery Energy Storage System (BESS) using Li-ion batteries can be employed to economically overcome these problems. It is also noted that the cost of batteries with longer discharge capacity is on the decline and their use is expected to be become economical in about 10 years. Looking at the reported pathway to satisfy The Paris Agreement, a 2-phase pathway is suggested. In the Phase 1 (2020–2030) 30% integration of intermittent renewables with BESS backup can be implemented in a manner that is not economically burdensome whilst the remaining fossil fuel system can provide the firm energy needed. In Phase 2 (2030–2055), more renewables can be implemented, provided sufficient long term storage, including batteries, can be added to provide firm energy. By 2030 the cost of such storage is expected to fall resulting in increased deployment without a financial burden to the islands. Ideally, during the period 2020 to 2055, there should be no new additions of fossil fuel plants and retiring plants should be replaced by renewable energy plants; although an account is necessary for plants already in the planning and development stages. The leeway period of 2020–2030 should be used for the preparation and planning of adding up to 100% renewables in all sectors. • Sensitivity of isolated island grid systems to intermittent renewables. • Demonstration of frequency regulation control using simulations of Li-ion battery storage. • Mitigation pathway utilizing 100% renewable to limit temperature rise to 1.5″.C [ABSTRACT FROM AUTHOR]