Reference monitors
The following three charts derive from data measured by reference monitors.  This high quality data is "ratified" up to the end of 2023.  Its source is Air Quality England.  The charts indicate that, although concentrations of nitrogen dioxide ("NO2") are declining, concentrations of particulate matter ("PM10" and "PM2.5") are not.  They also indicate that those concentrations are at or better than the World Health Organisation ("WHO") guideline for PM10 (which may be surprising  (- they also exceed PM2.5 concentrations by very little), they are worse than WHO guideline for PM2.5 and, at two of the three sites monitored, more than double the WHO guideline for NO2.  

Diffusion tubes
The following charts show how the annual average concentration of NO2 has changed since 2016 at sites being monitored long-term using difusion tubes in Luton.  The tables between the charts indicate the location of the sites shown by (the local authority's) code numbers.  This information derives from the local authority's Air Quality Annual Status Reports (as at the end of June 2024, the most recent data is for 2021, which one might think reflects lack of interest by the leadership of the local authority).

The data shown includes estimates where the source data is either missing or likely to be erroneous.  The data shown is "raw" - it has not been "adjusted for bias". Assuming no bias, annual average concentrations in the vicinity of the airport have declined substantially since early 2020 (in part due to covid-related restrictions on flying).  Elsewhere in Luton, concentrations have decreased rather less and the trend to the end of 2022 was generally flat.  Average concentrations across 2022 exceeded the UK legal limit at only one site, but tended to be between two and three times greater than the World Health Organisation guideline.  That guideline reflects health whereas the long-standing UK legal limit seems to reflect political convenience and disinterest.