Since July 2017, NO2 concentrations have been measured every second month at representative sites across St John's Wood - in the wards of Abbey Road and Regent's Park.  The cost of diffusion tubes for the first year's measurements was covered by the amenity society for St John's Wood.  The cost for the subsequent years has been supported by Westminster City Council from the ward budgets of those two wards.

The results are available from the website of the St John's Wood Society.

Much of the population of the two wards lives adjacent busy roads, where as the charts indicate, NO2 concentrations are greatest.  If other things were equal, this would presumably depress property values and related rents - if air quality at alternative addresses in other parts of Westminster or London is less unhealthy.  Much of the pollution derives from through traffic - and management of two of those roads is the remit of GLA (TfL).  Implicitly therefore, Westminster City Council can do little to either minimise traffic flows (without displacement into quieter streets) or minimise the nitrogen dioxide emissions of that traffic. Short of adopting the tactics of Extinction Rebellion (arguably laudable given government negligence concerning climate change), residents can perhaps achieve little by altering their own choices.

The chart below illustrates trens in NO2 concentrations reported by HS2 for a number of locations in and around St John's Wood.