round the world, Covid lockdowns have led to improvements in air pollution. In northern India, the Himalayas were visible in the distance for the first time in a generation. And during the first nine weeks of the UK lockdown, nitrogen dioxide along London’s roads decreased by an average of 31% compared with the pre-lockdown period. Non-essential shops in the capital reopened on 15 June but life and traffic pollution have still not returned to normal. Compared with 2019, decreases of more than 40% have been measured along roads in the City of London and Westminster, including the Strand and West End. This builds on the improvements from London’s ultra-low emission zone. But there are emerging signs of a return to pre-lockdown pollution on some suburban roads. The town of Horley, north-east of Gatwick, has recorded a 60% reduction in residential areas close to the airport fence and about 40% in a nearby children’s playground. UK government measurement equipment near Heathrow detected a 46% improvement. The biggest reduction was 64%, recorded near the entrance to the Beech Street tunnel, which is closed to diesel and petrol traffic. • Thanks to Timothy Baker, Louise Mittal and Anna Font, London Air and Imperial College London for discussion and coding assistance.