Air China planes are parked at the Capital International Airport, in Beijing, China, on March 17, 2020. EPA
Images show the fluctuation of nitrogen dioxide emissions across Europe from January 2020 until March 11, 2020. European Space Agency / Reuters
Maps show nitrogen dioxide (NO2) values across China from January 1-20, 2020 (before the quarantine) and February 10-25 (during the quarantine) which illustrates a significant decrease in NO2 over China. NASA / Earth Observatory / AFP
Maps show NO2 values over the Chinese city of Wuhan during three periods in 2020: (L-R, top row) from 01 to 20 January (before Lunar New Year), from 28 January to 09 February (around New Year celebrations), and from 10 to 25 February (after the event). NASA / EPA
A Chinese woman wears a mask to protect against pollution as she passes the CCTV building in heavy smog on December 8, 2015 in Beijing, China. Getty Images
Chinese women wear protective masks as they pass the CCTV building on their way to work on February 17, 2020 in Beijing, China. . Getty Images
Air China planes are parked at the Capital International Airport, in Beijing, China, on March 17, 2020. EPA
Images show the fluctuation of nitrogen dioxide emissions across Europe from January 2020 until March 11, 2020. European Space Agency / Reuters
Maps show nitrogen dioxide (NO2) values across China from January 1-20, 2020 (before the quarantine) and February 10-25 (during the quarantine) which illustrates a significant decrease in NO2 over China. NASA / Earth Observatory / AFP
Maps show NO2 values over the Chinese city of Wuhan during three periods in 2020: (L-R, top row) from 01 to 20 January (before Lunar New Year), from 28 January to 09 February (around New Year celebrations), and from 10 to 25 February (after the event). NASA / EPA
A Chinese woman wears a mask to protect against pollution as she passes the CCTV building in heavy smog on December 8, 2015 in Beijing, China. Getty Images
Chinese women wear protective masks as they pass the CCTV building on their way to work on February 17, 2020 in Beijing, China. . Getty Images
Air China planes are parked at the Capital International Airport, in Beijing, China, on March 17, 2020. EPA