The lockdown measures implemented worldwide to slow the spread of the COVID–19 pandemic have allowed for a unique real-world experiment, regarding the impacts of drastic emission cutbacks on urban air quality. In this study we assess the effects of a 7-week (23 March–10 May 2020) lockdown in the Greater Area of Athens, coupling in situ observations with estimations from a meteorology-atmospheric chemistry model. Measurements in central Athens during the lockdown were compared with levels during the pre- and post-lockdown 3-week periods and with respective levels in the four previous years. We examined regulatory pollutants as well as CO₂, black carbon (BC) and source-specific BC components. Models were run for pre-lockdown and lockdown periods, under baseline and reduced-emissions scenarios. The in-situ results indicate mean concentration reductions of 30–35% for traffic-related pollutants in Athens (NO₂, CO, BC from fossil fuel combustion), compared to the pre-lockdown period. A large reduction (53%) was observed also for the urban CO₂ enhancement while the reduction for PM_2.5 was subtler (18%). Significant reductions were also observed when comparing the 2020 lockdown period with past years. However, levels rebounded immediately following the lift of the general lockdown. The decrease in measured NO₂ concentrations was reproduced by the implementation of the city scale model, under a realistic reduced-emissions scenario for the lockdown period, anchored at a 46% decline of road transport activity. The model permitted the assessment of air quality improvements on a spatial scale, indicating that NO₂ mean concentration reductions in areas of the Athens basin reached up to 50%. The findings suggest a potential for local traffic management strategies to reduce ambient exposure and to minimize exceedances of air quality standards for primary pollutants.

Athens, Greece has been in economic and social crises after the 2008 global recession, resulting in an increase in wood burning as a cheaper method of residential heating in the winter. Reducing wood burning emissions is a source-specific method to address air quality degradation, and indirectly climate change, through instituting policies aimed at human health co-benefits. In this work, we investigate and quantify the potential health co-benefits from policies reducing outdoor particulate matter (PM) pollution from residential wood burning by assessing the pollution conditions during the 2015 calendar year in Athens, Greece, emphasizing vulnerable populations. We conducted a systematic literature search to extract data regarding effective improvements to outdoor PM due to wood burning interventions, and get a range of potential ambient PM reduction estimates regarding realistic benefits from different interventions. We applied a health impact assessment methodology and used existing Athens specific data to calculate the preventable daily average non-accidental deaths associated with reducing PM, additionally considering low and high socioeconomic status (SES) groups. We found that the reduction in outdoor PM concentration showed the potential to benefit lower SES groups as much as 13.5 times more than the high SES group, representing an opportunity for policies to improve not only the health of the total population but also improve environmental equity and health disparities.

While Earth observation (EO) increasingly provides a multitude of solutions to address environmental issues and sustainability from the city to global scale, their operational integration into the Sustainable Development Goals (SDG) framework is still falling behind. Within this framework, SDG Indicator 11.6.2 asks countries to report the “annual mean levels of fine particulate matter (PM_2.5) in cities (population-weighted)”. The official United Nations (UN) methodology entails aggregation into a single, national level value derived from regulatory air quality monitoring networks, which are non-existent or sparse in many countries. EO, including, but not limited to remote sensing, brings forth novel monitoring methods to estimate SDG Indicator 11.6.2 alongside more traditional ones, and allows for comparability and scalability in the face of varying city definitions and monitoring capacities which impact the validity and usefulness of such an indicator. Pursuing a more harmonised global approach, the H2020 SMURBS/ERA-PLANET project provides two EO-driven approaches to deliver the indicator on a more granular level across Europe. The first approach provides both city and national values for SDG Indicator 11.6.2 through exploiting the Copernicus Atmospheric Monitoring Service reanalysis data (0.1° resolution and incorporating in situ and remote sensing data) for PM_2.5 values. The SDG Indicator 11.6.2 values are calculated using two objective city definitions—“functional urban area” and “urban centre”—that follow the UN sanctioned Degree of Urbanization concept, and then compared with official indicator values. In the second approach, a high-resolution city-scale chemical transport model ingests satellite-derived data and calculates SDG Indicator 11.6.2 at intra-urban scales. Both novel approaches to calculating SDG Indicator 11.6.2 using EO enable exploration of air pollution hotspots that drive the indicator as well as actual population exposure within cities, which can influence funding allocation and intervention implementation. The approaches are introduced, and their results frame a discussion around interesting policy implications, all with the aim to help move the dial beyond solely reporting on SDGs to designing the pathways to achieve the overarching targets.

Cities face a wide variety of pressures, many of which negatively impact the health of both the environment and citizens and require an integrated smart city approach to address. By infusing state-of-the-art Earth observation (EO) into tools for cities, the SMart URBan Solutions for air quality, disasters and city growth (SMURBS) project produced a portfolio of smart solutions based off of and refined by continued engagement and co-design with stakeholders and cities to address real needs, gaps, and issues. This portfolio of EO-driven solutions serves as an openly available archive and depository of city solutions for environmental pressures and aims to enhance urban resilience and sustainability, and therefore, make cities smarter. Within this paper, we describe the SMURBS experience of bringing together city stakeholders and EO experts and building the portfolio of smart urban solutions, concluding with the six foundational aspects distilled from this experience to serve as a playbook for solution builders to ensure the production of fit-for-purpose and effective city solutions.