When world leaders arrive in Beijing, the city typically lays on beautiful blue skies.
It's a sign of the Chinese capital's ability to control its notorious smog when it needs to. It's also indicative of the progress China has made in tackling air pollution in recent years, both by shutting down and upgrading elderly factories and passing new restrictions to tackle emissions.
That's seen Beijing fall out of the top 100 most-polluted cities in Asia in recent years, with overall pollution levels 10% lower across Chinese cities between 2017 and 2018, according to a report by Greenpeace and AirVisual. Shanghai, the country's largest city and financial capital, has also made environmental advances, such as adopting stringent recycling regulations. At 146 globally on the AirVisual list, Wuhan, in northeastern China, is not among China's most polluted cities, but residents aren't taking any chances. Recent weeks have seen major protests there -- in themselves a rarity in China -- over plans for a new garbage incineration plant.