Certainly, London's air has gotten noticeably cleaner in recent years. Although I suspect most of this gain is from incentivising zero-emission vehicles through

Certainly, London's air has gotten noticeably cleaner in recent years. Although I suspect most of this gain is from incentivising zero-emission vehicles through the congestion charge exemption and also the ULEZ ultra-low emission zone (an additional charge on older dirty vehicles), not just from reducing traffic volumes.