A study published in The Lancet Wednesday suggests London's attempts to improve air quality have worked, but they haven't helped children who already have poor lung health.
The city started establishing what's called a low-emission zone in 2008 when it fined drivers of cars that didn't meet emission requirements. Researchers say particulate levels have stayed the same since then. Those levels can lead to premature death and make heart and lung disease worse.
The study says researchers saw some reduction of people with rhinitis, which is irritation and swelling of the mucous membrane. But they didn't see any improvement of asthma symptoms or the amount of children with small lungs.
London will start implementing an "ultra-low-emission zone" by 2021 with stricter exhaust emission standards that will include a larger area of London.
Additional reporting from Newsy affiliate CNN.