COVID-19 was not taken seriously by many of us until the wave hit our countries and impacted daily life routines and travel plans, similar to our responses to climate change. COVID-19 led to a decrease of anthropogenic activities in Turkey, largely due to lockdown. Changes in the air quality index (AQI) were assessed before and during coronavirus. In this study, the authors investigated the changes of AQI for 2.5 mu m particulate matter (PM2.5), a primary air pollutant, as well as ozone, a secondary air pollutant, in Turkey during December 2019, April 2020, and May 2020. Overall, the PM(2.5)index improved by 34.5% by the end of April 2020. However, the ozone index increased from 16.8 to 28.8 by the end of April. The increase in ozone is attributed to the reduction of PM levels, which increased sunlight penetration. Before COVID-19, the AQI for Turkey was categorized as unhealthy for sensitive groups (PM2.5 = 103); however, during the pandemic, AQI fell to lower boundaries of the moderate category by May 2020 (PM2.5 = 56.9). Changes in municipal wastewater were also assessed. Municipal wastewater quality and hospital waste generation did not change during the pandemic in Turkey. Therefore, we should not expect COVID-19 risks in treatment plant effluents. This study gives confidence to regulators that when strict measures are implemented, air quality can improve.