In its ruling made public Wednesday, the ASA said consumers would understand Hyundai’s advertising to mean that “the car overall had negligible environmental impact and would remove impurities from the air as it was driven, such that no impurities caused by driving it would remain in the air.”

Although Hyundai made the case to the ASA that its claim was based on the car having an on-board air-purification system that filters gases and fine dust, the authority said the ad must not appear again. While the Nexo doesn’t emit exhaust like vehicles that run on internal combustion engines, it still releases particulates as a result of brake and tire wear.

The ruling is a reminder that shifting to electric and hydrogen fuel cell-powered cars won’t completely do away with transportation emissions. Particles from brakes, tires and road-surface wear are responsible for well over half of particulate pollution from road transport, according to the government’s Air Quality Expert Group.

Britain has been in breach of its own national and European Union air-quality rules for years. Last year, a coroner for the first time ruled that air pollution was a significant factor in the cause of a death — a 9-year-old girl in south London.

Prime Minister Boris Johnson announced late last year that the U.K. will stop allowing sales of new cars that run only on gasoline and diesel engines from 2030, and require that all new vehicles be fully electric from 2035.