48 is decent - at the high end of the "good" range - but AQI fluctuates a lot from day to day. There were some fires on the other side of the continent from me and that was enough to bump the AQI here above 80.

Here's a report with some longer term trends (warning: 2MB PDF download): https://www.london.gov.uk/media/105046/download . Air pollution is down across London, and sharply so on the most proximate roadside sensors.