The number of Londoners living in areas where nitrogen dioxide is at an illegal level has fallen by 94% from early 2017 to early 2020, The Guardian reports, as a result of environmental measures such as instigation of the ultralow emission zone (Ulez). Dr Gary Fuller, an air pollution expert at the Centre, noted that these changes in NO2 emissions shows the reversibility of the air pollution problem, which is notable, as 99% of London still has particle pollution levels above the World Health Organization’s recommended limits.