Red double-decker buses, icons of London streets, are in trouble for creating more smog than they used to. Ironically, the culprits are filters fitted to the buses in a bid to make the city’s air cleaner by eliminating their choking black exhaust fumes.
The problem is that the filters are changing the chemistry of exhaust gases, resulting in increased emissions of nitrogen dioxide, one of the key components of urban smog. So despite a reduction in London’s overall traffic achieved by imposing controversial congestion charges, air quality is failing to meet European smog targets more often than before.
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