The COVID-19 epidemic discovered and reported at the end of December 2019 and began spreading rapidly around the world . The impact of the COVID-19 event on the trip intensity, AQI (air quality index), and air pollutants, including PM2.5, PM10, SO2, CO, NO2, and O3in Shenzhen, Guangzhou, and Foshan (the so-called ‘ three cities ’) from January 12 to March 27, in 2019 and 2020, are compared and discussed . In 2020, the combined trip intensity in the three cities ranged between 0.73 and 5.54 and averaged 2.57, which was 28.4% lower than that in 2019 . In terms of the combined AQIs for the three cities, from January 12 to March 26 , 2020, the daily AQIs ranged between 21.0 and 121.3 and averaged 56.4, which was 16.0% lower than that in 2019 . The average AQIs in order were Guangzhou (57.5) > Foshan (54.1) > Shenzhen (44.1). In 2019, the distribution proportions of the six AQI classes were 45.2% , 50.4% , 4.40% , 0% , 0%, and 0%, respectively, while those in 2020 were 62.7% , 37.3% , 0% , 0% , 0% and 0%, respectively . For the combined data for the three cities, on the top five days with the highest AQIs during the epidemic period, the average concentrations of PM2.5, PM10, SO2, CO, NO2, and O3were 76.4 µg m–3 , 113.4 µg m–3 , 5.14 ppb , 0.88 ppm , 36.5 ppb and 55.5 ppb, which were 55.2% , 49.4% , 55.1% , 30.0% , 45.1% and 15.5% lower than those during the non-epidemic period (from January 12 to March 27 , 2017–2019). The above results revealed that the comprehensive strict epidemic prevention and control actions reduced trip intensity and improved the air quality significantly.