How bad is China’s air pollution?

Another outstanding example is Beijing, widely studied and appreciated by UN agencies and other international agencies. About a decade or two ago, Beijing had the dubious distinction of consistently ranked the most polluted city in the world, with PM 2.5 well in excess of 100. Its smog was notorious, driving many multinational companies and diplomatic missions to seriously consider and publicly speak about relocating out of Beijing. Even though China as a whole ranked quite poorly in international pollution rankings, it put in highly focused and major efforts into tackling air pollution in Beijing. It moved all coal-based power plants and industries out of the city, it ensured phasing out of older and more polluting vehicles, and introduced low-Emission Zones in the city where only the cleanest or electric vehicles were allowed, an idea also enforced in London and other European cities. Beijing has been transformed from a car-centred city to what agencies have described as an example of sustainable mobility, expanding urban rail, bicycle and pedestrian mobility. A major afforestation effort was also taken in the northern regions from where recurring dust-storms bringing fine dust into Beijing were curbed. Widespread use of domestic coal-burning stoves was also curbed. As a result of all these measures, Beijing’s air pollution levels have been reduced by almost half its earlier levels, also bringing down pollution in the huge extended tri-city “megapolis” area.

From https://peoplesdemocracy.in/2023/1112_pd/annual-air-pollution-festival

It was really bad at one point but it has improved a lot in the decade. This is because of a concerted effort to limit car proliferation and focus on renewable sources of energy. Here in India on the other hand the air in the cities is nigh toxic and there are no signs of improving. Where I live there were signboards installed that showed the air quality index. Over the past year or so they have stopped showing this index and only use it to show the weather because it used to say "very dangerous almost all the time".

Edit: this is only Beijing though. I will try to find some more info.

From https://www.sciencedirect.com/science/article/pii/S0301479723013130

Our study used a large and comprehensive sample of Chinese energy and macroeconomics data over a period of 32 years. Our findings provide important insights into the relationship between energy sources and air pollution in China, which has significant implications for global policy and market debates. Specifically, our Granger causality results show that as China's economy grows, air pollution levels decrease as the use of renewable energy increases. Also, the implementation of stricter environmental regulations by the Chinese government has increased the use of renewable energy sources and this has Granger-caused a reduction in air pollution levels. The results are consistent with both the EKC theory and the Porter Hypothesis. Our findings suggest that China may be approaching the turning point on the EKC, where economic growth leads to an improvement in environmental quality. At the same time, the Porter Hypothesis is supported, showing that the implementation of stricter regulations can incentivise the country to invest in research and development for more efficient and cleaner production processes, which can ultimately lead to improved air quality. These findings have significant international implications for global policy and market debates related to carbon neutralisation and sustainable energy transitions. However, the study also reveals that China's economy still heavily relies on non-renewable energy sources, indicating a need for continued efforts to shift towards cleaner energy sources in the country. The results of this study have important implications for policymakers and industries in China, and globally, emphasising the need for continued investment in renewable energy sources and the promotion of innovation to achieve carbon neutralisation.

I am not sure how legit this EKC turning point theory is because a big reason why Western economies were able to improve environmentally was because they outsourced the "dirty work" to the global south. China improving air quality by the magnitude they are achieving is unprecedented in the global south and therefore the world. It should continue to improve even more in my estimation.

they've been making a large effort to decreasing air pollution in their cities, in many its visibly disappeared

https://www.unep.org/interactive/beat-air-pollution/ United Nations

In the winter of 2016, the air pollution in our city(Jinan) was very serious，Haze was like a real silent hill.In recent years, the air quality is excellent or good for most days of the year.