The following charts illustrate trends in emissions of the two air pollutants having greatest current concern, nitrogen dioxide ("NO2") as particulate matter - specifically  PM10 and PM2.5.   They refer to reference quality data, the source of which is Air Quality England.  As such, they exclude data provided by that source for "sensors" - which generate an indication of the concentrations of those air pollutants.
(The Lakeside Osiris site is not the same as the Lakeside site.)