clch - smog particles and lockdown

Comparison of particulates pollution [main cause of urban smog] in the UK during the 2020 lockdown, with the average figures for 2015-19. Data from nine conurbations. There are some striking images showing the clearer air during Lockdowns.
The main source of these particulates will be internal combustion engines, specifically old and poorly maintained diesels, but also from the oil-burning by some older petrol engines. Also, some public transport vehicles are contributing to this problem. Plus, using fuel oil for heating buildings and some industrial processes can add to the smog.
Unfortunately, re-opening the economy without choosing "greener" transport etc modes has reversed the situation, so any gains [reduction in pollution] was very shortlived.
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Not my Image ; Fair Use & public information