www.nature.com/npjUrbanSustain ARTICLE OPEN A take-home message from COVID-19 on urban air pollution reduction through mobility limitations and teleworking Alba Badia1, Johannes Langemeyer1,2,3, Xavier Codina4, Joan Gilabert 1,5,6 , Nacho Guilera4, Veronica Vidal 1,7 , Ricard Segura 1 , Mar Vives4 and Gara Villalba 1,8 ✉ The rigorous traffic limitations during COVID-19 have forced many people to work from home, reaching an outstanding degree of teleworking and reduction in air pollution. This exceptional situation can be examined as a large-scale pilot test to determine the potential of improving urban air quality through teleworking. Based on observed traffic reductions during the COVID-19 lockdown in Barcelona, we formulate socio-occupational scenarios, with various configurations of teleworking, and simulate them using the chemistry transport model WRF-Chem with multi-layer urban scheme. By intensifying teleworking to 2, 3, and 4 days a week, averaged NO2 concentrations are reduced by 4% (−1.5 μg m−3), 8% (−3 μg m−3), and 10% (−6 μg m−3), respectively, while O3 increases moderately (up to 3 μg m−3). We propose that teleworking be prioritized and promoted as an effective contribution towards reduction of long-term urban air pollution and short-term pollution peaks. npj Urban Sustainability (2021)1:35 ; https://doi.org/10.1038/s42949-021-00037-7 1234567890():,; INTRODUCTION caused pollution levels to drop significantly. This was first The ongoing pandemic of coronavirus disease 2019 (COVID-19) observed in China, where satellite images of emissions showed a has hit humanity hard and by surprise1. To slow down the spread decrease of NO2 emissions by 30%10,11, and was later reported of the virus, radical measures have been implemented, among from many parts of the world12–15. The European Environmental them an extraordinary limitation of people’s movement—never Agency has been tracking the weekly average concentrations of seen to this extent at global scale2. Under an imminent threat to air pollutants (NO2, Particulate Matter with a diameter of ≤10 µm human lives, scientific evidence, media warnings, bottom-up (PM10, PM2.5) of many European cities where restrictive measures campaigns, and decisive political action have led to drastic have been implemented16, showing that most cities reduced measures to radically limit mobility as a way to mitigate the contamination levels by 30–50% compared with the same period expansion of COVID-19. Now—as calls to return to ‘normality’ are in 2019. In addition, estimated averaged emissions reduction in becoming louder around the globe—we should raise some critical Europe during the COVID-19 lockdown were reported (−33% for nitrogen oxides (NOx), −8% for non-methane volatile organic thought on which kind of normality we want to return to. Here we compounds, −7% for sulfur oxides (SOx), and −7% for PM2.5) with want to reflect upon lessons learned from the COVID-19 mitigation an 85% contribution of the road transport to the total reductions measures in terms of reduced mobility and teleworking and its expect for SO2 for which reductions were mainly driven by the joint effect on urban air pollution. As sharp drops in air pollution energy and manufacturing industry sectors17. Overall, most of the during confinement periods indicate, COVID-19 experiences may studies show a correlation between the reduction in mobility data teach us some important lessons about how the deadly global air and trend of PM2.5 and NO217,18. These observations prompt us to pollution crisis might be overcome. More than 80% of the people think that if we are able to enhance teleworking and reduce traffic living in urban areas are exposed to air quality levels that do not emissions so drastically and promptly to stop the spread of the meet air quality standards of the World Health Organization3, with COVID-19 we are capable of taking similar measures to stop other populations in low-income cities being most impacted4. In the deadly diseases related to the poor air-quality in cities. It seems European Union (EU-28) it was estimated that long-term exposure timely to question whether we need to move back to the deadly to elevated Particulate Matter with a diameter of ≤2.5 µm (PM2.5) ‘pre-corona’ configuration of urban traffic and emission patterns, concentrations were responsible for about 374,000 premature and whether it would be possible to establish similar traffic deaths in 2016; exposure to enhanced nitrous oxide (NO2) and restrictions as during the pandemic in order to reduce premature ozone (O3) levels led to ~68,000 and 14,000 additional premature deaths from air pollution. It is important to reflect to which extent deaths, respectively5. Moreover, the finding of some recent studies our commuting and travels really are essential, and to which show that short-term and long-term exposure to air pollution, extent we can implement teleworking to avoid traffic emissions, as especially PM2.5 and NO2, contribute to aggravating COVID-19 evidenced during the confinement period. infections and mortalities6–8. Traffic emissions typically contribute A first observation from the large scale COVID-19 lockdown 30–45% to urban air pollution9. Consequently, COVID-19 mitiga- indicates that people in many sectors are capable of building up tion measures that included important reduction of traffic have resilience to the limitation of traveling to work, and—despite 1 Sostenipra Research Group, Institute of Environmental Sciences and Technology, Universitat Autònoma de Barcelona, Barcelona, Spain. 2Barcelona Lab for Urban Environmental Justice and Sustainability (BCNUEJ), Urban Hospital del Mar Medical Research Institute (IMIM), Barcelona, Spain. 3Department of Geography, Humboldt Universität zu Berlin, Berlin, Germany. 4Solució de Ciutat i Territori d’Anthesis Lavola, Rambla Catalunya, 6, 2ª planta, Barcelona, Spain. 5PCOT Team, Institute Cartographic and Geological of Catalonia (ICGC), Barcelona, Spain. 6GAMA Team Department of Applied Physics, University of Barcelona (UB), Barcelona, Spain. 7Departament d’Arquitectura de Computadors i Sistemes Operatius (CAOS), Escola d’Enginyeria, Universitat Autònoma de Barcelona, Barcelona, Spain. 8Department of Chemical, Biological and Environmental Engineering, Universitat Autònoma de Barcelona, Barcelona, Spain. ✉email: gara.villalba@uab.cat Published in partnership with RMIT University A. Badia et al. 2 indisputable frictions—adapt to new modes of work without the during the second quarter of 2020, 16.20% of employed people requirement of physical displacements, including both daily worked from home for more than half of the days, compared to travels to work by car as well as air-bound travels19. During the 4.81% observed in 201930. This comparison illustrates the lockdown, we could observe first-hand how the higher education potential of tele-workable jobs that were not previously run sector has started to professionalize forms of online teaching20, remotely. while scientific conferences are increasingly held virtually. Also, In short, the exceptional situation during COVID-19 can be public administrations start to arrange new data management understood as a large-scale pilot test of the implementation of systems accessible remotely and many white-collar workers in teleworking and related traffic reduction, in order to reduce air industries and services are experiencing that they can fulfill most pollution levels in cities. The objective of this article is to further of their duties as well from their home-offices. Even medical examine the potential of future socio-occupational scenarios in doctors have started teleworking via telephone and internet- reducing air pollution in cities. We focus our analysis on NO2 based consultancies21. Figures from Google (2020) observing concentrations where we see the biggest changes due to mobility during the COVID-19 lockdown2 indicate that the teleworking. Variability in O3 concentrations is also analyzed due presence at work spaces dropped by over 60% in countries to the role of NOx in O3 loss and production. where strict lockdown measures enforced a maximum of teleworking, such as in Spain or Italy. In the EU and overall global north, with over 70% of the people RESULTS working in the service sector, we must start to question much Study case stronger which parts of the usual level of daily displacements are To discuss the wider implications of enhanced teleworking and really necessary. The current crisis is teaching us that for many targeted traffic restrictions to improve urban air quality in cities, people daily commuting is related to habits and traditions in we study the Metropolitan Area of Barcelona (AMB), Spain, during organizing their work rather than to actual necessities and the strict confinement in spring 2020. The AMB has more than 5 therefore a rethink of how to restructure work in a more air- million people and is the most populated urban area on the pollution-efficient way is required. We should keep in mind that Mediterranean coast and one of the largest metropolis in Europe. metropolis, which generate and attract a great number of Barcelona annually reports one of the highest air pollution levels 1234567890():,; motorized displacements, are currently the areas where the main Europe-wide31, with the most problematic pollutants being PM2.5, air quality problems are happening22. Teleworking (not only PM10, and NO231–33. In particular, in 2019 the NO2 annual mean avoiding commuting to and from home, but also replacing exceeded the WHO guideline3 and the legal limit in the UE of meetings with video calls) entails an important reduction of those 40 μg m−3 in the urban air pollution ground monitoring stations emissions related to mobility23,24. An extensive review of the representing high traffic (Eixample and Gràcia-Sant Gervasi). Also energy impacts of teleworking by Hook et al.24 summarizes that that year, the mean value for PM10 and PM2.5 was above the the energy savings from reduced commuter travel are greater WHO guideline3 of 20 and 10 μg m−3, respectively in all urban than the indirect energy consumption associated with changes in stations in the city31. In the city of Barcelona alone, the excess of non-work travel and home energy consumption. A study of air pollution beyond the recommended WHO guidelines was Switzerland traffic congestion determined that teleworking was deemed responsible for 7% of natural mortalities (about 1000 responsible for 1.9% reduction of the air pollution and concluded annual deaths), 11% of new lung cancer cases and 33% of new that teleworking is a promising tool for urban planning and childhood asthma cases in 201933. Road traffic is the main source development to reduce traffic volume and improve air quality23. of NOx, responsible for 59% of all emissions in the AMB, while the This study in particular shows that the largest changes in air seaport is the second largest emission source with 16%34. pollutants concentrations due to teleworking are observed for The complex topography of the AMB is characterized by inland NO2 with a 3.6% reduction, followed by 3.4% for CO, 3.3% for PM mountain ranges (Fig. 1) protecting the area from Atlantic and between 2.1 and 2.3% for O3 and SO2. Another study of a advections and continental air masses, but also blocking the teleworking scenario in the United States shows that increased dispersion of pollutants35, while the valleys of the rivers Llobregat teleworking decreases CO2 emissions by 2–80%, NOx by 20–100%, and Besòs play an important role in the creation of air-flow PM10 by 10–100%, and CO by 20–100%25. Teleworking practices patterns32. Thus, the atmospheric flow at AMB is complicated not have been gaining momentum in digital-based jobs as a means to only by the urban heat island effects but also topographic flows increase job satisfaction and productivity26,27 and are expected to and sea breezes which influence air pollution and human health. experience rapid growth in the future28. As one of the countries hardest hit by COVID-19, the mobility We are at an important turning point in the conception of restrictions during the COVID-19 lockdown in Spain2 were among telework. The European Commission in a recent communication the strictest globally; only manufactory and warehouse workers, highlights the important role of telework in preserving jobs and farmers, supermarket clerks and nursing staff were permitted to production in the context of the Covid-19 crisis29. The COVID commute as they were deemed essential to maintain the core pandemic has weakened some of the limiting factors of functions of the society, such as the provision of food, energy, teleworking, and we can now conceive future socio-occupational health care, and internet among others. Maintaining these basic scenarios in which telework is more recurrent. Among the factors functions required about 36% of the displacements to workspaces that have previously limited a greater proliferation of telework, the compared to the pre-corona business-as-usual, according to the most important are lack of specific regulations as well as lack of Google mobility reports for Catalonia for March 20202. Similar to willingness by managers and workers alike. The crisis situation other urban areas in Europe, the economy in the AMB is caused by the outbreak of COVID-19 has led many companies to dominated by the tertiary sector (90.1% of salaried jobs and use telework as an emergency solution, in order to be able to 88.3% of the self-employed) and showed a general potential to continue many non-essential productive activities19. Additionally, reduce traffic significantly without losing the maintenance of basic progress has been made on other aspects that were previously functions, at least for a short period of time. limiting, such as information and communication technologies to facilitate telework, and the transition to a more knowledge- intensive economy. COVID-19 has also encouraged online over COVID-19 mobility reduction and improved air quality face-to-face education, as well as a widespread reduction in Observational data from various urban and suburban monitoring personal mobility. For instance, according to the Labor Force stations throughout the AMB (Fig. 1) indicate that the COVID-19 Survey (EPA) of the National Statistics Institute (INE) of Spain, lockdown during March and April 2020 significantly reduced npj Urban Sustainability (2021) 35 Published in partnership with RMIT University A. Badia et al. 3 Fig. 1 Metropolitan Area of Barcelona as a study case for air pollution reduction. Smaller map: location of domain used for the simulation of regional chemistry transport model WRF-Chem (black frame), and the area of study the AMB (red frame). Larger map: a more detailed map of the AMB indicating the urban and suburban air pollution monitoring stations (Xarxa de Vigilància i Previsió de la Contaminació Atmosfèrica, XVPCA). principal air pollutants, including NO2, PM10 and SO214,36. We percentile) went down from values around 80–20 μg m−3 (at 8 h), illustrate Monday–Friday hourly averages of NO2 concentrations in and from 65 to 10 μg m−3 (at 21 h). Fig. 2 for 2020 (in blue) and 2019 (in orange) for the highly intense We also find that the low pressures and cyclonic weather traffic area monitored by the Eixample air pollution station (red associated to low pressures seen in weeks 3, 6, 7, 9, 12, 13 of 2020 square in Fig. 1). These 2 years had similar stable surface pressures (see Supplementary Table 1 for more information) enhance gas (1016 hPa in both cases), temperature anomalies (around 2 °C in dispersion thereby reducing pollutant concentrations, while 2019 and 2.5–3 °C in 2020), and low winds, albeit 2019 was a drier higher pressures have the opposite effect. This is clearly seen year (please refer to Supplementary Table 1 and Supplementary when comparing the third and fourth week of the lockdown with Table 2 for a detailed report of the meteorological conditions for similar mobility reductions (84.4%), yet during the fourth week we the study period for both years). Just the same, to reduce the can see higher NO2 concentrations during morning peaks (from influence of the meteorological conditions on the comparison, 18–20 to 55–57 μg m−3). Hence, traffic reductions are not the only cause for lower air pollution levels during the COVID-19 lockdown, the hourly averages presented for 2019 are calculated based on evidencing a significant role of the meteorological conditions in the entire month, rather than week by week as it is shown for reducing the concentrations of air pollutants. 2020. Furthermore, we include a weekly estimation of the mobility Unlike NO2, Ozone (O3) levels increased during the period of reduction based on Google COVID-19 Community Mobility confinement in the AMB. During the fourth week of the lockdown Reports2. For example, the mobility reduction during the first we can observe the most pronounced O3 peak at 16 h with a and second week of the confinement, 75.4% and 82.2% median value of 150 μg m−3, approximately double that of April respectively, caused a reduction of NO2 concentration of 53% 2019. The remaining weeks the ozone values are also clearly and 59%, respectively, compared to 2019. During the third week higher than in 2019. Ozone is not reduced as the other pollutants of the lockdown, with the highest mobility reduction (84.4%), NO2 as a consequence of three combined effects37,38: (1) decrease of concentrations were observed to drop down to 21 μg m−3 during NOx in a volatile organic compounds (VOCs)-limited (low VOC/NOx morning peak hour, a 75% reduction when compared to March ratios) urban environment might cause O3 to increase, as opposed 2019. Reductions were especially distinctive during the typical to the behavior at the rural-regional background, which is mainly daily pollution peaks around 8 and 21 h when the medians (50th NOx-limited (high VOC/NOx ratios); (2) reducing nitrogen oxide Published in partnership with RMIT University npj Urban Sustainability (2021) 35 A. Badia et al. 4 Fig. 2 NO2 and O3 concentration during COVID-19 mobility restrictions. Variation for NO2 and O3 concentrations during COVID-19 confinement and phase-out weeks (in blue) and the same month for the year 2019 (orange), observed at Eixample air quality monitoring station (as part of the Xarxa de Vigilància i Previsió de la Contaminació Atmosfèrica, XVPCA). Blue and orange lines show the medians (50th percentile) and shaded zones show the 10th/90th percentiles. An estimation of the reduction in travel by vehicleduring 2020 is provided underneath each panel, source: Google mobility reports (https://www.google.com/covid19/mobility/). (NO) levels slows down the ozone (O3) consumption (titration of monitoring network: Xarxa de Vigilància i Previsió de la O3, NO + O3 = NO2 + O2) and causes an increase of O3 concentra- Contaminació Atmosfèrica, XVPCA) over the AMB for NO2 and tions; and (3) the usual increase of insolation and temperatures O3 (see Supplementary Figs. 1 and 2). Overall, the model shows a from February to April leads to an increase in O3. reasonable agreement with the observations during the period of Consequently, O3 concentrations during lockdown exceeded March, although there are specific periods archiving significant the maximum value established by the WHO, which is 100 μg m−3 biases (−35 and 26 μg m−3, for NO2 and O3, respectively) over the averaged over an 8-h period. This enhancement of O3 was also urban stations representing high traffic (Eixample, Gràcia-Sant found in other cities during the COVID-19-related mobility Gervasi and Poblenou). However, the model exhibits low biases restrictions10,14,39. Overall, however, the observations evidence a (−20 and 12 μg m−3, for NO2 and O3, respectively) at stations significant improvement of the air quality due to the restrictive located in a low traffic area (Ciutadella, Vall d’Hebron, Palau Reial mobility measures14. For a more detailed description of air quality and Sants) for specific periods. Surface NO2 and O3 concentrations during the confinement and de-confinement phases of COVID-19 are very sensitive to the emissions, therefore, these model biases for Barcelona, please visit www.urbag.eu/news/. are mostly due to the low resolution in our emission inventory. Based on the perturbed emissions simulations, we estimate that city-wide NO2 concentrations during a severe lockdown scenario Air pollution modeling are reduced by as much as 52% (22 μg m−3) during the typical The simulation of the base scenario March 2016 using morning high pollution peak between 7 and 9 h, as shown in Fig. 4 HERMESv3 shows that the highest NO emission peaks occur in (and in Supplementary Fig. 3), comparable to the observations the central parts of the AMB during the morning and afternoon (as during the COVID-19 lockdown (weeks 1–7 in Fig. 2). Similarly, the can be appreciated in Fig. 3B, C, E, F), due to the high medium confinement scenario reduces NO2 concentrations by concentration of traffic throughout the day. Once NO is emitted, 33% (13 μg m−3), comparable to weeks 8 through 10 (Fig. 2). As it is rapidly converted to NO2 in the presence of O3 through was observed during the fourth week of confinement, reductions oxidation reactions that take place in less the tenths of of NOx emissions alleviate the effect of ozone titration37,38 leading seconds37,38. This conversion depends on the concentration of to a significant increase in O3 concentrations for the lockdown O3 and VOCs, solar energy, and meteorological conditions37,38. The scenario up to 61% (18 μg m−3) and under the medium WRF-Chem simulations indicate that the highest NO2 concentra- confinement scenario up to 35% (11 μg/m3) (see Supplementary tions are observed in the north of the AMB (Fig. 3A, D) due to the Figs. 4 and 5). In some areas of the AMB, these extreme mobility combination of the atmospheric northward plume characteristic reduction scenarios are thus partly counterproductive in terms of of this area and the complex topography (Fig. 1) that pulls the alleviating air pollution, since O3 levels exceed the daily maximum pollutants towards the north of the AMB during both morning and 8-h mean of 100 μg m−3. On the contrary, the low confinement evening peaks. scenario results in 16% reduction of NO2 concentrations (−6 μg The simulation of the base case scenario has been evaluated m−3) and an increase of O3 concentrations (+5 μg m−3). Although with several air quality monitoring stations (that belong to the we cannot make a direct correlation between emission reduction npj Urban Sustainability (2021) 35 Published in partnership with RMIT University A. Badia et al. 5 Fig. 3 NO2 pollution peaks in the Metropolitan Area of Barcelona (AMB). Average NO2 concentrations (A, D), NO total (B, E) and traffic emissions (C, F) for the base scenario during morning (top panels) and afternoon (bottom panels) peaks time for March 2016 (only weekdays Monday–Friday). The peak time for the concentrations is 7–9 h (morning) and 21–23 h (afternoon). The peak time for the emissions is 6–8 h (morning) and 15–17 h (afternoon). and resulting pollutant concentrations because atmospheric the north of the AMB where higher pollution is found during the chemistry is not only influenced by changes in emissions but day (see Fig. 3). also by atmospheric dynamics such as transport, we can infer In short, teleworking can be a key tool in alleviating traffic some conclusions based on the simulations. Results show that by congestion during peak time and improve air quality in a short intensifying teleworking efforts to 2 and 3 days a week, NO2 term (days–weeks) particularly in the urban areas, where high concentrations are reduced, averaging reductions over the entire population density and the hotspots for traffic emissions AMB of 4% (−1.5 μg m−3) and 8% (−3 μg m−3) in the low and are found. moderate increase telework scenarios, respectively. We also find that during high pollution episodes air quality over all the AMB DISCUSSION region improves by changing from 2 days per week telework (low- increase telework scenario) to 4 days a week (high-increase Mobility restrictions implemented worldwide to contain and delay the spread of the COVID-19 epidemic have drastically reduced telework scenario) with an overall 10% reduction (−6 μg m−3) and traffic2 and corresponding emissions, and effected on reducing air a slight increase of up to 3 μg m−3 of O3 concentrations. pollution levels10–15,36. In particular, we observe that NO2 Similar results are seen during the typical evening high concentration values in the city of Barcelona during COVID-19 pollution peaks between 21 and 23 h shown in Fig. 5 (and in mobility restrictions were below the WHO thresholds which had Supplementary Fig. 6), where a full lockdown scenario reduces the been exceeded at several urban air pollution monitoring stations NO2 concentrations by as much as 53% (−27 μg m−3) and during the same period in previous years31. The COVID-19 inspired increases O3 by 70% (+25 μg m−3), see Supplementary Figs. 7 modeling efforts to indicate that air pollution reduction might be and 8) comparable to the observed concentrations during weeks 1 reached relatively easily through enhanced teleworking. Although through 7 (Fig. 2). The medium confinement scenario simulation these figures are still premature, and a more in-depth investiga- shows NO2 concentration reduction of 35% (−17 μg m−3) similar tion is required as to whether productivity standards can be to weeks 8, 9, and 10 of the confinement periods (Fig. 2). The low maintained under teleworking conditions and whether other confinement scenario results in 13% reduction of NO2 concentra- environmental costs emerge (e.g. less efficient use of space and tions and an increase of O3 concentrations (up to 8 μg m−3). Note other resources, doubling of equipment etc.), urban policy makers that there is a slight increase in NO2 (1 μg m−3) and decrease of O3 should question how they can better target their instruments, and (1 μg m−3) for the moderate and low telework scenarios around which incentives they can provide and which restrictions can be the harbor area that could be related to local O3–NOx changes in implemented to maintain some of the positive effects on air reducing traffic emissions. In general, reductions for all scenarios pollution we are seeing during COVID-19. This might include more are seen over all the territory with higher reductions located on flexible work schedules, starting with the public administration, Published in partnership with RMIT University npj Urban Sustainability (2021) 35 A. Badia et al. 6 Fig. 4 NO2 concentration differences during morning peak hours. Difference (in %) in NO2 concentrations between the base case and each scenario during typical morning high pollution peak hours (7–9 h) in the Metropolitan Area of Barcelona for March 2016 (only weekdays days Monday–Friday). possibly tax advantages for home offices to lower the general bans of older cars as imposed by LEZ as well as fuel tax reforms emission level, up to targeted traffic restrictions for low priority tend to discriminate those with lower income41. Emission travels when threshold levels for air pollution are surpassed. The reductions based on mandatory teleworking might be socially COVID-19 lockdown observations and our corresponding simula- more equal and partly compensate for unequal emission patterns tion indicate that a 25% emission reduction scenario during among different social groups, for example, in relation to leisure- periods of high pollution is achievable, simply based on the related travels. Apart from that, teleworking allows for flexible maximization of teleworking and reducing other work-related schedules and a greater work-life balance while reducing the travel and shopping. To the contrary, stronger traffic reductions mobility. Therefore, teleworking might also reduce the amount of related to 50 and 75% emission reduction scenarios seem to accidents a (both in itinere and in labore)42,43 and lower other embed an unintended feedback manifested in an increase of O3 economic, social and environmental costs linked to the current concentrations, and thus not seem to be appropriate measures. mobility model44. Besides, the Covid-19 crisis shows us how Our study provides the empirical and modeled evidence to intensively promote teleworking as a means to lower urban teleworking has been used by companies to provide a safe and pollution levels. Annual average NO2 concentrations have healthy working environment to their employees’ and the repeatedly exceeded maximum permissible values over the last continuity to economic activity19. 5 years in some stations of the AMB, consequently causing In short, COVID-19 has opened an important opportunity to re- thousands of premature deaths34,40. Results show that by think more radically, measures and opportunities to combat the intensifying teleworking efforts to 2, 3, and 4 days a week, NO2 urban air pollution crisis we are facing in cities. Policies that steer concentrations are reduced, averaging reductions over the entire people’s mobility by enhancing teleworking might not only be AMB during the day of 4% (−1.5 μg m−3), 8% (−3 μg m−3), and efficient in decreasing emissions and easily implemented, but are 10% reduction (−6 μg m−3). Indeed, teleworking can be an also likely to be more socially equitable than other measures effective solution to reduce traffic and improve air quality, which primarily used for this purpose until today. can be implemented immediately leveraging on our experience during the COVID-19 mobility restrictions and in addition to other mitigation strategies such as Low Emissions Zones (LEZ). Unlike METHODS LEZs, teleworking can be implemented much more rapidly and Future socio-occupational scenarios furthermore reduces the amount of fossil fuel consumed and In order to understand the effect of mobility on air quality during the consequently the carbon footprint of the city. lockdown and to explore the potential of teleworking towards air pollution The COVID-19 period has shown that in general higher-paid reduction, we define six scenarios with traffic emission reductions resulting jobs have higher adaptive capacities for teleworking. This means from various degrees of teleworking and reduced private vehicle use. mandatory teleworking will more strongly affect well-paid white- Based on the justified estimates that 85% of the labor force of the AMB is collar workers. While other instruments to lower emissions, such as dedicated to the service sector45, and that ~40% of all personal vehicle npj Urban Sustainability (2021) 35 Published in partnership with RMIT University A. Badia et al. 7 Fig. 5 NO2 concentration differences during evening peak hours. Difference (in %) in NO2 concentrations between the base case and each scenario during typical evening high pollution peak hours (21–23 h) in the Metropolitan Area of Barcelona for March 2016 (only weekdays days Monday–Friday). transit is work-related46, we define the following three scenarios of (5) Medium confinement = 50% traffic emission reduction: Resulting enhanced telework: from 55% reduction of private vehicle use for work-related travel (accomplished by teleworking 4 days a week and reducing other (1) Low increase in telework = 5% traffic emission reduction: Requires work-related vehicle activity by 20%). Additionally, online education 7.5–12.5% decrease in work-related traffic, obtained by 20% of the avoids 20% of private vehicle use, and people reduce driving for labor force of the service sector adopting teleworking 2 days a week, shopping by 40%. Vehicle use related to personal activities such as resulting in an overall 5% reduction of traffic-related emissions leisure, accompaniment, and health-related appointments are all (40% × 0.20 × 2/5). reduced between 50 and 70%. (2) Moderate increase in telework = 10% traffic emission reduction: (6) Severe lockdown = 75% emission reduction: Resulting from 55% Requires 17.5–25% decrease in work-related traffic; obtained by 30% reduction of private vehicle use for work-related travel (accom- of the labor force of the service sector teleworking 3 days a week, plished by teleworking 4 days a week and reducing other work- resulting in an overall 7.2% reduction of traffic-related emissions related vehicle activity by 20%). Additionally, online education (40% × 0.30 × 3/5 and rounded up to 10% to account for additional avoids 100% of private vehicle use, and people reduce driving for work-related trips that are avoided during teleworking days). shopping by 70%. Vehicle use related to personal activities such as (3) High increase in telework = 15% traffic emission reduction: Requires leisure, accompaniment, and health-related appointments are all 32.5–37.5% decrease in work-related traffic; obtained by 40% of the reduced between 75 and 100%. This scenario seems only feasible labor force of the service sector teleworking 4 days a week, resulting during short periods of time and during absolute extreme situations. in an overall 12.8% reduction of traffic-related emissions (40% × This simulation serves as a comparison of model simulation with 0.40 × 4/5 and rounded up to 15% to account for additional work- observations. related trips that are avoided during teleworking days). Telework also allows business meetings to be conducted remotely Moreover, we define three additional scenarios combining reduction of personal and occupational mobility in addition to without the taking long business trips by airplane. In order to represent in teleworking, to replicate behaviors seen during the main COVID-19 a simple way these remotely business trips, air traffic has also been confinement stages of severe lockdown (March 16th–April 30th, see reduced in each scenario with the same reduction as road traffic. Fig. 1 weeks one through seven), medium confinement (May 1st–June 12th, see Fig. 1 weeks 8 through 13), and low confinement Air quality modeling (June 12th onwards, see Fig. 1 week 14). All calculations are made The regional chemistry transport model WRF-Chem48 version 4.1, a highly based on the mobility report published by Autoritat del Transport Metropolità de l’Àrea de Barcelona47. flexible community model for atmospheric research where (4) Low confinement = 25% traffic emission reduction: Resulting from aerosol–radiation–cloud feedback processes are taken into account, is used 45% reduction of private vehicle use for work-related travel in this study. The WRF-Chem model has been previously used for simulations (accomplished by teleworking 4 days a week and reducing other of air pollution episodes49–51. For the gas-phase chemical scheme, we used work-related vehicle activity by 15%). Additionally, online education the Regional Acid Deposition Model (RADM252) and the MADE/SORGAM avoids 20% of private vehicle use, and people reduce driving for aerosol scheme53,54. RADM2 has been broadly used in air quality studies over shopping by 30%. No reductions are in effect for leisure and Europe55,56. The model is set up with a horizontal resolution of 3 × 3 km and personal travel. 45 vertical layers up to 100 hPa. The meteorological initial and lateral Published in partnership with RMIT University npj Urban Sustainability (2021) 35 A. Badia et al. 8 the form at https://www.acom.ucar.edu/wrf-chem/mozart.shtml (last access: 5 March Table 1. Model details and experiment configuration. 2020). The WRF-Chem simulation outputs, underlying Figs. 4–5 and Supplementary Figs. 1–8, are openly available via the Zenodo repository at https://doi.org/10.5281/ Model details zenodo.476730870. The WMS maps underlying Fig. 1 are available in GIS format via Gas-phase scheme RADM252 the Cartographic and Geological Institute of Catalonia at: https://www.icgc.cat/ca/ Administracio-i-empresa/Serveis/Geoinformacio-en-linia-Geoserveis/WMS-i-tessel-les- Aerosol particles MADE/SORGAM53,54 Cartografia-de-referencia/WMS-Mapes-i-ortofotos-vigents. The Butlletí climàtic men- Photolysis scheme FAST-J71 sual, supporting Supplementary Tables 1 and 2, is openly available from meteo.cat | Urban scheme BEP + BEM59 Servei Meteorològic de Catalunya: https://www.meteo.cat/wpweb/climatologia/el- clima-ara/butlleti-mensual/. The April 2019 and April 2020 versions were used in Biogenic emissions MEGANv265 the study. Experiment configuration Horizontal resolution 3 × 3 km Vertical layers 45, up to 100 hPa CODE AVAILABILITY 58 The WRF-Chem model code is available from https://www2.mmm.ucar.edu/wrf/users/ Chemical initial condition MOZART-4 downloads.html (last access: 13 November 2020), with the specific code used in this Meteorological initial condition FNL-NCEP57 study available from the authors upon request (Gara.Villalba@uab.cat). The Chemistry spin-up 1 month HERMESv3_GR model code is available from https://earth.bsc.es/gitlab/es/ hermesv3_gr. Emission inventories CAMS-REG-APv3.163 Received: 28 October 2020; Accepted: 1 July 2021; boundary conditions were determined using the Final Analysis (FNL) of the NCEP global model data57. Chemical initial and boundary conditions are from the global atmospheric model MOZART-4 global chemical model58. We conducted WRF-Chem simulations for March 2016 covering the Catalonia REFERENCES domain (see boundaries in Fig. 1) with a spin-up of 1 month. In order to 1. Wang, C., Horby, P. W., Hayden, F. G. & Gao, G. F. A novel coronavirus outbreak of represent the urban areas in our domain, here we used a multi-layer urban global health concern. Lancet 395, 470–473 (2020). canopy scheme, the Building Effect Parameterization (BEP) coupled with the 2. Google L. L. C. COVID-19 Community Mobility Reports. https://www.google.com/ Building Energy Model (BEP + BEM59) that takes into account the energy covid19/mobility/ (2020). consumption of buildings and anthropogenic heat, which has been 3. World Health Organization. Regional Office for Europe. Air quality guidelines previously validated for the area under study60. The Local Climate Zones global update 2005: particulate matter, ozone, nitrogen dioxide and sulfur dioxide. (LCZ) classification61 is used for the AMB which associates a specific value for Copenhagen: WHO Regional Office for Europe. https://apps.who.int/iris/handle/ each LCZ for thermal, radiative and geometric parameters of the buildings 10665/107823 (2006). and ground, which are used by the BEP + BEM urban canopy scheme to 4. World Health Organization. Air pollution levels rising in many of the world’s compute the heat and momentum fluxes in the urban areas. Eleven LCZs poorest cities. https://www.who.int/news/item/12-05-2016-air-pollution-levels- with specific urban morphology for each were added into the land- rising-in-many-of-the-world-s-poorest-cities (2016). cover map. 5. European Environmental Agency. Air quality in Europe—2019 report. No 10/ The HERMESv3 preprocessor tool62 was used in order to create the 2019. https://doi.org/10.2800/822355 https://www.eea.europa.eu/publications/ anthropogenic emissions files from the CAMS-REG-APv3.1 database63. air-quality-in-europe-2019/air-quality-in-europe-2019/viewfile#pdfjs. Biogenic emissions are computed online from the Model of Emissions of action=download (2019). Gases and Aerosols from Nature v2 (MEGAN64). Six air quality simulations 6. Gupta, A. et al. Air pollution aggravating COVID-19 lethality? Exploration in Asian are performed under each emission scenario (75, 50, 25 15, 10, and 5% cities using statistical models. Environ Dev Sustain 23, 6408–6417 (2021). reduction on traffic emissions) and compared with the base case scenario 7. Ali, N. & Islam, F. The Effects of Air Pollution on COVID-19 Infection and Mortality —A Review on Recent Evidence. Frontiers in Public Health 8, 580057 (2020). simulation (no reduction in traffic emissions) for the period of March 8. Pozzer, A. et al. Regional and global contributions of air pollution to risk of death 2016 to study the impact of the lockdown measures on air quality and from COVID-19. Cardiovasc. Res. 116, 2247–2253 (2020). how teleworking can improve the air pollution over the AMB. Simulations 9. Trombetti, M. et al. Spatial inter-comparison of Top-down emission inventories in are based on data from 2016, the most recent year for which emission European urban areas. Atmos. Environ. 173, 142–156 (2018). inventories are readily available. According to the meteorological data 10. Le, T. et al. Unexpected air pollution with marked emission reductions during the from the Servei Meteorològic de Catalunya65,66, the average surface COVID-19 outbreak in China. Science 369, 702–706 (2020). pressure was 1014.5 hPa for 2016 and 1016 hPa for 2020, the wind 11. Muhammad, S., Long, X. & Salman, M. COVID-19 pandemic and environmental intensity was low/moderate around 40 km/h (small trees in leaf begin to pollution: a blessing in disguise? Sci. Total Environ. 728, 138820 (2020). sway) for both periods, the temperature was 2.5–3 °C higher in 2020 and 12. Berman, J. D. & Ebisu, K. Changes in U.S. air pollution during the COVID-19 there was positive anomaly precipitation for both periods. Therefore, the pandemic. Sci. Total Environ. 739, 139864 (2020). simulations considered a similar period as the COVID-19 confinement 13. Sharma, S. et al. Effect of restricted emissions during COVID-19 on air quality in (16th March until 30th April) in terms of climate, atmospheric stability, India. Sci. Total Environ. 728, 138878 (2020). and synoptic conditions. Table 1 describes the main configuration of the 14. Tobias, A. et al. Changes in air quality during the lockdown in Barcelona (Spain) model and experiment configuration. one month into the SARS-CoV-2 epidemic. Sci. Total Environ. 726, 138540 (2020). 15. Gautam, S. The Influence of COVID-19 on Air Quality in India: A Boon or Inutile. Bulletin of Environ. Contam. Toxicol 104, 724–726 (2020). DATA AVAILABILITY 16. European Environmental Agency. Monitoring Covid-19 impacts on air pollution. The data generated and analysed during this study are described in the following https://www.eea.europa.eu/themes/air/air-quality-and-covid19/monitoring- data record: https://doi.org/10.6084/m9.figshare.1474379767. The data from Xarxa de covid-19-impacts-on Vigilància i Previsió de la Contaminació Atmosfèrica (XVPCA), underlying Figs. 1–2 17. Guevara, M. et al. Time-resolved emission reductions for atmospheric chemistry and Supplementary Figs 1–2, are openly available from Departament d’Acció modelling in Europe during the COVID-19 lockdowns. Atmos. Chem. Phys. 21, Climàtica, Alimentació i Agenda Rural: http://mediambient.gencat.cat/ca/ 773–797 (2021). 05_ambits_dactuacio/atmosfera/qualitat_de_laire/vols-saber-que-respires/ 18. Li, J. & Tartarini, F. Changes in Air Quality during the COVID-19 Lockdown in descarrega-de-dades/descarrega-dades-automatiques/ (last access 6 June 2021). The Singapore and Associations with Human Mobility Trends. Aerosol Air Qual. Res 20, CAMS emission data are available from Emissions of atmospheric Compounds and 1748–1758 (2020). Compilation of Ancillary Data (ECCAD) at https://doi.org/10.24380/m89g-j50868. The 19. Belzunegui-Eraso, A. & Erro-Garcés, A. Teleworking in the Context of the Covid-19 FNL-NCEP global model data are available from the National Center for Atmospheric Crisis. Sustainability 12, 3662 (2020). Research (NCAR) Research Data Archive at https://doi.org/10.5065/978H-D23969. The 20. Mishra, L., Gupta, T. & Shree, A. OnlineTeaching-Learning in Higher Education MOZART-4 global data are hosted by the NCAR and are available upon request via during Lockdown Period of COVID-19 Pandemic. Int. J. Educ. Res. 1, 100012 (2020). npj Urban Sustainability (2021) 35 Published in partnership with RMIT University A. Badia et al. 9 21. Webster, P. Virtual health care in the era of COVID-19. The Lancet 395, 1180–1181 49. Georgiou, G. K. Air quality modelling in the summer over the eastern Medi- (2020). terranean using WRF-Chem: chemistry and aerosol mechanism intercomparison. 22. World Health Organization. Health as the pulse of the new urban agenda: United Atmos. Chem. Phys. 18, 1555–1571 (2018). Nations conference on housing and sustainable urban development, Quito, 50. Yegorova, E. A. Characterization of an eastern U.S. severe air pollution episode October 2016. World Health Organization. https://apps.who.int/iris/handle/ using WRF/Chem. J. Geophys. Res. 116, D17306 (2011). 10665/250367 (2016). 51. Shrivastava, M. et al. Modeling organic aerosols in a megacity: comparison of 23. Giovanis, E. The relationship between teleworking, traffic and air pollution. Atmos. simple and complex representations of the volatility basis set approach. Atmos. Pollut. Res 9, 1–14 (2018). Chem. Phys. 11, 6639–6662 (2011). 24. Hook, A., Court, V., Sovacool, B. K. & Sorrell, S. A systematic review of the energy 52. Stockwell, W. R., Middleton, P., Chang, J. S. & Tang, X. The second generation and climate impacts of teleworking. Environ. Res. Lett. 15, 093003 (2020). regional Acid Deposition Model chemical mechanism for regional air quality 25. Kitou, E. & Horvath, A. Energy-related emissions from telework. Environ. Sci. modeling. J. Geophys. Res. 95, 16343–16367 (1990). Technol. 37, 3467–3475 (2003). 53. Ackermann, I. J. et al. Modal aerosol dynamics model for Europe: Development 26. Coenen, M. & Kok, R. A. W. Workplace flexibility and new product development and first applications. Atmos. Environ. 32, 2981–2999 (1998). performance: the role of telework and flexible work schedules. Eur. Manag. J 32, 54. Schell, B., Ackermann, I. J., Hass, H., Binkowski, F. S. & Ebel, A. Modeling the 564–576 (2014). formation of secondary organic aerosol within a comprehensive air quality model 27. Visser, J. & Ramos Martin, N. Expert Report on the Implementation of the system. J. Geophys. Res. 106, 28275–28293 (2001). Social Partner’s Framework Agreement on Telework. http://www.uva-aias.net 55. Im, U. et al. Evaluation of operational online-coupled regional air quality models (2008). over Europe and North America in the context of AQMEII phase2. Part I: ozone. 28. Cegarra-Leiva, D., Sánchez-Vidal, M. E. & Cegarra-Navarro, J. C. Work Life Balance Atmos. Environ. 115, 404–420 (2015). and the Retention of Managers in Spanish SME’s. Int. J. Hum. Res. Manag. 23, 56. Tuccella, P. et al. Modeling of gas and aerosol with WRF/Chem over Europe: 91–108 (2012). Evaluation and sensitivity study. J. Geophys. Res. 117, D03303 (2012). 29. European Semester: Commission Communication on Country Specific Recom- 57. National Centers for Environmental Prediction/National Weather Service/NOAA/ mendations. https://ec.europa.eu/info/publications/2020-european-semester- U.S. Department of Commerce. NCEP FNL Operational Model Global Surface commission-communication-country-specific-recommendations_en (2020). Analyses. Research Data Archive at the National Center for Atmospheric Research, 30. National Statistics Institute of Spain. Labour Force Survey; 2nd Quarter 2020. Computational and Information Systems Laboratory. https://rda.ucar.edu/ https://www.ine.es/CDINEbase/consultar.do?mes=&operacion=EPA.% datasets/ds083.2/ (1997). 20Resultados%20trimestrales&id_oper=Ir&L=1 (2020). 58. Emmons, L. K. et al. Description and evaluation of the Model for Ozone and 31. Rico, M. et al. Informe qualitat de l’aire de Barcelona, Technical report. Agència de Related chemical Tracers, version 4 (MOZART-4), Geosci. Model Dev 3, 43–67 Salut Pública de Barcelona. (2019). (2010). 32. Massagué, J. et al. 2005–2017 ozone trends and potential benefits of local 59. Salamanca, F. & Martilli, A. A new Building Energy Model coupled with an Urban measures as deduced from air quality measurements in the north of the Barce- Canopy Parameterization for urban climate simulations-part II. Validation with lona metropolitan area. Atmos. Chem. Phys., 19, 7445–7465 (2019). one dimension off-line simulations. Theor. Appl. Climatol. 99, 345–356 (2010). 33. Rivas, I. et al. Child exposure to indoor and outdoor air pollutants in schools in 60. Ribeiro, I., Martilli, A., Falls, M., Zonato, A. & Villalba, G. Highly resolved WRF-BEP/ Barcelona, Spain. Environ.Int. 69, 200–212 (2014). BEM simulations over Barcelona urban area with LCZ. Atmos. Res. 248, 105220 34. Schembari, A. et al. Traffic-related air pollution and congenital anomalies in (2021). Barcelona. Environ. Health Perspect. 122, 317–323 (2014). 61. Guevara, M., Tena, C., Porquet, M., Jorba, O. & Pérez García-Pando, C. HERMESv3, a 35. Soriano, C., Baldasano, J. M., Buttler, W. T. et al. Circulatory Patterns of Air Pol- stand-alone multi-scale atmospheric emission modelling framework – Part 1: lutants within the Barcelona Air Basin in a Summertime situation: Lidar and global and regional module. Geosci. Model Dev. 12, 1885–1907 (2019). Numerical Approaches. Boundary-Layer Meteorology 98, 33–55. https://doi.org/ 62. Stewart, I. D. & Oke, T. R. Local Climate Zones for Urban Temperature Studies. Bull. 10.1023/A:1018726923826 (2001). Amer. Meteor. Soc. B93, 1879–1900 (2012). 36. Baldasano, J. M. COVID-19 lockdown effects on air quality by NO2 in the cities of 63. Granier, C. et al. The Copernicus Atmosphere Monitoring Service global and Barcelona and Madrid (Spain). Sci.Total Environ. 741 (2020). regional emissions. Copernicus Atmosphere Monitoring Service (CAMS) report. 37. Sillman, S. The relation between ozone, NOx and hydrocarbons in urban and https://doi.org/10.24380/d0bn-kx16 (2019). polluted rural environments. Atmos. Environ. 33, 1821–1845 (1999). 64. Guenther, A. B. et al. The Model of Emissions of Gases and Aerosols from Nature 38. Monks, P. S. et al. Tropospheric ozone and its precursors from the urban to the version 2.1 (MEGAN2.1): an extended and updated framework for modeling global scale from air quality to short-lived climate forcer. Atmos. Chem. Phys. 15, biogenic emissions. Geosci. Model Dev. 5, 1471–1492 (2012). 8889–8973 (2015). 65. Servei Meteorològic de Catalunya (SMC). Butlletí climàtic mensual Abril 2016. 39. Sicard, P. Amplified ozone pollution in cities during the COVID-19 lockdown. Sci. Departament de Territori i Sostenibilitat. https://static-m.meteo.cat/wordpressweb/ Total Environ. 735, 139542 (2020). wp-content/uploads/2015/06/26072356/Butllet%C3%AD-abril2016.pdf (2016). 40. Nieuwenhuijsen, M. J. et al. Air pollution, noise, blue space, and green space and 66. Servei Meteorològic de Catalunya (SMC). Butlletí climàtic mensual Abril 2020. premature mortality in Barcelona: a mega cohort. Int. J. Environ. Res. Public Health. Departament de Territori i Sostenibilitat. https://static-m.meteo.cat/wordpressweb/ 15, 2405 (2018). wp-content/uploads/2021/03/01155111/Butllet%C3%AD-Abril2020_v3.pdf (2020). 41. Zimmer, A. & Koch, N. Fuel consumption dynamics in Europe: Tax reform 67. Badia, A. et al. Metadata record for the article: A take-home message from COVID- implications for air pollution and carbon emissions. Transp. Res. Part A: Policy and 19 on urban air pollution reduction through mobility limitations and teleworking. Practice 106, 22–50 (2017). Figshare https://doi.org/10.6084/m9.figshare.14743797 (2021). 42. Metropolitan Transport Authority. Mobility Strategy of the Metropolitan Trans- 68. National Centers for Environmental Prediction/National Weather Service/NOAA/ port Authority, Àrea de Barcelona. https://doc.atm.cat/ca/_dir_pde/ U.S. Department of Commerce. 1997. NCEP FNL Operational Model Global Sur- 20190404_Estrategia_Mobilitat_ATM.pdf (2019). face Analyses. Research Data Archive at the National Center for Atmospheric 43. Dima, A.-M., Țuclea, C.-E., Vrânceanu, D.-M. & Țigu, G. Sustainable Social and Research, Computational and Information Systems Laboratory. https://doi.org/ Individual Implications of Telework: A New Insight into the Romanian Labor 10.5065/978H-D239 (last access: 5 March 2020). Market. Sustainability 11, 3506 (2019). 69. Granier, C. et al. The Copernicus Atmosphere Monitoring Service global and 44. Botzoris, G. N., Profillidis, V. A., & Galanis, A. T. Teleworking and Sustainable regional emissions. ECCAD https://doi.org/10.24380/m89g-j508 (2019). Transportation in the Era of Economic Crisis. Proceedings of the 5th Interna- 70. Badia, A. WRF-Chem output- NO2 and O3 concentrations for the base case and tional Virtual Scientific Conference. https://doi.org/10.18638/ictic.2016.5.1.295 each emission scenario. Zenodo https://doi.org/10.5281/zenodo.4767308 (2021). (2016). 71. Wild, O., Zhu, X. & Prather, M. J. Fast-J: Accurate Simulation of In- and Below- 45. Indicadors de la Unió Europea, Institut d’Estadística de Catalunya. www.idescat. Cloud Photolysis in Tropospheric Chemical Models. J. Atmos. Chem. 37, 245–282 cat/indicadors/?id=ue&n=10110 (2019). (2000). 46. Enquesta de mobilitat en dia feiner 2019 (EMEF). https://observatori.atm.cat/ enquestes-de-mobilitat/Enquestes_ambit_ATM/EMEF/2019/ EMEF_2019_Informe_AMB.pdf (2019). 47. Autoritat del Transport Metropolità de l’àrea de Barcelona, Observatori de la ACKNOWLEDGEMENTS Movilitat, Enquestes de movilitat. https://www.atm.cat/web/ca/observatori/ This work has been made possible thanks to the financial support of the ERC enquestes-de-mobilitat.php Consolidator Integrated System Analysis of Urban Vegetation and Agriculture (818002- 48. Grell, G. A. Fully coupled “online” chemistry within the WRF model. Atmos. URBAG) and the Spanish Ministry of Science, Innovation and Universities, through Environ. 39, 6957–6975 (2005). the “Maria de Maeztu” programme for Units of Excellence (CEX2019-000940-M). Published in partnership with RMIT University npj Urban Sustainability (2021) 35 A. Badia et al. 10 This research has been supported by MINECO-Spain (TIN2017-84553-C2-1-R), and by Correspondence and requests for materials should be addressed to G.V. the Spanish government grant PRE2018-085425. The authors thankfully acknowledge the computer resources at PICASSO and the technical support provided by the Reprints and permission information is available at http://www.nature.com/ Universidad de Málaga (RES-AECT-2020-2-0004). The authors further wish to thank reprints XVPCA for the provision of measurement stations. Also, thanks to the free use of HERMESv3_GR and the developing team for their support. We also thank the Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims Copernicus Global and Regional emissions service for the emission inventory. in published maps and institutional affiliations. AUTHOR CONTRIBUTIONS J.L. and G.V. devised the research. A.B., J.L. and G.V. initiated the study; A.B. developed Open Access This article is licensed under a Creative Commons and performed the WRF-Chem simulations and analyzed the model output. V.V. Attribution 4.0 International License, which permits use, sharing, analyzed the observational datasets. A.B., J.L. and G.V. wrote the manuscript with adaptation, distribution and reproduction in any medium or format, as long as you give contributions from all authors. appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the COMPETING INTERESTS article’s Creative Commons license and your intended use is not permitted by statutory The authors declare no competing interests. regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons. org/licenses/by/4.0/. ADDITIONAL INFORMATION Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s42949-021-00037-7. © The Author(s) 2021 npj Urban Sustainability (2021) 35 Published in partnership with RMIT University