Fig. 5From: Air quality index variation before and after the onset of COVID-19 pandemic: a comprehensive study on 87 capital, industrial and polluted cities of the worldPercentage change of AQI-CO and O3 between 2020 during the lockdown period and 2019 and 2021 in different cities in the world. A AQI-CO variation and B AQI-O3 variationBack to article page