The Quality Urban Label (QUL) as a Tool for Accelerating Carbon Neutrality in Cities: The 4Q and 5E City Model ^†

Simple indicators are often used to summarize the complexity of systems or products, commonly through color-coded labels paired with letters. These labels, like those indicating energy efficiency or nutritional ratings, help users quickly understand essential characteristics. Building on this approach, the Quality Urban Label (QUL) has been developed to assess public space adaptation to urban climate change. The QUL utilizes four key indicators, called quality components 4Q: air quality (pollutants), noise pollution, thermal comfort, and visual comfort. It ranges from 0 to 25 and is represented by a color and letter code (green, A, ranging from 0 to 2; blue, B, ranging from 6 to 11; orange, C, ranging from 15 to 19; and red, D, ranging from 22 to 25), with green representing better quality and red poorer quality. The QUL aims to evaluate public spaces based on energy consumption reduction, greenhouse gas emissions reduction, and progress toward carbon neutrality. To achieve this 4Q model, five interconnected levers are proposed for cities to develop, and the five levers are proposed to be named as the 5E levers: efficiency, renewable energy production and consumption, electrification of end use, circular economy, and CO₂ ensnaring (capture). Each lever encompasses projects and initiatives capable of directly or indirectly capturing urban CO₂ and accelerating the reduction in greenhouse gas emissions. These levers are interlinked, providing a road map for constructing a coherent and sustainable municipal model and reaching the 4Q city model.