Evaluation of air quality effects of the London ultra-low emission zone by state-space modelling

In April 2019, an ultra-low emission zone (uLEZ) was implemented in London to tackle road transport air pollution. In this study, a state-space intervention model is developed for the first time to quantify the effects of this policy on London air quality. For developing this model, hourly NO, NO2, and NOx concentrations at 28 monitoring stations across London for 12 months before the uLEZ intervention and 11 months following it were used. Additionally, this model accounts for the influences of the meteorological variables of temperature, wind speed, and humidity, as well as those of the day of the week and calendar month.