Air quality has improved dramatically in industrial megacities across the world, thanks to mass economic shutdowns because of the Covid-19 virus - environmentalists fear smokey skies will return once lockdowns are relaxed. Industrial cities like Buenos Aires, Beijing and Milan are seeing the unusual sight of blue skies because factories have closed. Residents, however, believe this will be short-lived. Buenos Aires, for example, has seen a 60% reduction in polluting gasses in the last few months, while Shanghai, China, has seen a 20% drop in emissions. Milan, which recently was covered in a blanket of smog so thick that the government had to encourage "car-free days", has clear skies.Environmentalists fear, however, that the drop in emissions will be seen by industries as leeway to push manufacturing harder once normalcy resumes.