The upper chart of the two which follow show how the annual average concentration of NO2 changed between 2009 and 2018 at prominent sites in the Borough of Hammersmith and Fulham.  The lower chart refers to data for a second set of sites, from February 2017.
(- the data derive from monthly measurements by diffusion tubes;  sites whose names are presented in green font now have concentrations below the current legal limit, concentrations at those in brown are illegal):

 
Source:  based on monthly data abstracted from the Council’s Air Quality Annual Status Reports and a report of the London Wide Environment Programme

Source:  based on monthly data abstracted from the Council’s Air Quality Annual Status Reports for 2017 & 2018

The data in the two charts above indicate that NO2 concentrations tended to decline at most of the sites prior to 2018, since when the trend has reversed.