The researchers studied air quality in three cities in central China from 2017 to 2019 and looked at how the COVID-19 pandemic affected air pollution levels in early 2020. They found that air quality was better in 2020 compared to previous years, with lower levels of pollutants like PM2.5 and NO2. The pandemic led to a decrease in pollution, especially in February 2020, when levels were significantly lower than in the same month in previous years. However, O3 levels did not decrease as much because of the interaction with NO2. Overall, the study shows that the COVID-19 pandemic had a positive impact on air quality in the three cities.