tl;dr: A five-year study of 3,400 children found that London kids' previously stunted lung growth accelerated to match those in less-polluted Luton after the 2019 introduction of the Ultra Low Emission Zone, with clinically impaired lung capacity dropping from 14% to 9%. Researchers linked the improvement to faster reductions in nitrogen dioxide exposure in London, though independent experts caution that Covid-era changes and behavioral shifts (like more walking/cycling) could also be factors. Published in Lancet Public Health, the study is being called the strongest evidence yet that clean air zones can reverse pollution damage in children.